ISSN: 2346-3775

Vol. 6 No. 1

October 2017 – January 2018

Published by:

Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia

In cooperation with:

Chinese Academy of Tropical Agricultural Sciences (CATAS)

International Center for Tropical Agriculture (CIAT) retains copyright of articles with the work simultaneously licensed under the e Creative Commons Attribution 4.0 International License (to view a copy of this license, visit creativecommons.org/licenses/by/4.0/).

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Editors

Rainer Schultze-Kraft,

Lyle Winks,

International Center for Tropical Agriculture (CIAT),

Former editor of “Tropical Grasslands”,

Colombia

Australia

Management Committee

Changjun Bai,

Rainer Schultze-Kraft,

Chinese Academy of Tropical Agricultural Sciences

International Center for Tropical Agriculture (CIAT),

(CATAS),

Colombia

P.R. China

Cacilda B. do Valle,

Robert J. Clements,

Empresa Brasileira de Pesquisa Agropecuária (Embrapa),

Agricultural Consultant,

Brazil

Australia

Lyle Winks,

Asamoah Larbi,

Former editor of “Tropical Grasslands”,

International Institute of Tropical Agriculture (IITA),

Australia

Nigeria

Michael Peters,

International Center for Tropical Agriculture (CIAT),

Colombia

Editorial Board

Changjun Bai,

Albrecht Glatzle,

Chinese Academy of Tropical Agricultural Sciences

Iniciativa para la Investigación y Transferencia de

(CATAS),

Tecnología Agraria Sostenible (INTTAS),

P.R. China

Paraguay

Caterina Batello,

Orlando Guenni,

Food and Agriculture Organization of the United Nations

Universidad Central de Venezuela (UCV),

(FAO),

Venezuela

Italy

Jean Hanson,

International Livestock Research Institute (ILRI),

Michael Blümmel,

Ethiopia

International Livestock Research Institute (ILRI),

India

Michael David Hare,

Ubon Ratchathani University,

Robert J. Clements,

Agricultural Consultant,

Thailand

Australia

Mario Herrero,

Commonwealth Scientific and Industrial Research

Myles Fisher,

Organisation (CSIRO),

International Center for Tropical Agriculture (CIAT),

Australia

Colombia

Masahiko Hirata,

Bruce Pengelly,

University of Miyazaki,

Agricultural Consultant,

Japan

Australia

Peter Horne,

T. Reginald Preston,

Australian Centre for International Agricultural Research

University of Tropical Agriculture Foundation (UTA),

(ACIAR),

Colombia

Australia

Johann Huguenin,

Kenneth Quesenberry,

Centre de Coopération Internationale en Recherche

University of Florida,

Agronomique pour le Développement (CIRAD),

USA

France

Max Shelton,

Muhammad Ibrahim,

University of Queensland,

Centro Agronómico Tropical de Investigación y Enseñanza

Australia

(CATIE),

Costa Rica

Werner Stür,

Australian Centre for International Agricultural Research

Asamoah Larbi,

(ACIAR),

International Institute of Tropical Agriculture (IITA),

Australia

Nigeria

Carlos E. Lascano,

Cacilda B. do Valle,

Universidad Nacional de Colombia - Sede Bogotá,

Empresa Brasileira de Pesquisa Agropecuária (Embrapa),

Colombia

Brazil

Robert Paterson,

Agricultural Consultant,

Spain

Principal Contacts

Rainer Schultze-Kraft

International Center for Tropical Agriculture (CIAT)

Colombia

Phone: +57 2 4450100 Ext. 3036

Email: r.schultzekraft@cgiar.org

Technical Support

José Luis Urrea Benítez

International Center for Tropical Agriculture (CIAT)

Colombia

Phone: +57 2 4450100 Ext. 3354

Email: CIAT-TGFT-Journal@cgiar.org

Table of Contents

Review Papers

Tropical forage legumes for environmental benefits: An overview

1-14

Rainer Schultze-Kraft, Idupulapati M. Rao, Michael Peters, Robert J. Clements, Changjun Bai, Guodao Liu

Research Papers

Soil attributes of a silvopastoral system in Pernambuco Forest Zone

15-25

Hugo N.B. Lima, José C.B. Dubeux Jr, Mércia V.F. Santos, Alexandre C.L. Mello, Mário A. Lira, Márcio

V. Cunha

Germination of tropical forage seeds stored for six years in ambient and controlled temperature

26-33

and humidity conditions in Thailand

Michael D. Hare, Naddakorn Sutin, Supuaphan Phengphet, Theerachai Songsiri

Evaluation of growth parameters and forage yield of Sugar Graze and Jumbo Plus sorghum

34-41

hybrids under three different spacings during the maha season in the dry zone of Sri Lanka

Hajarooba Gnanagobal, Jeyalingawathani Sinniah

Variation in carbohydrate and protein fractions, energy, digestibility and mineral concentrations in

42-52

stover of sorghum cultivars

Sultan Singh, B. Venktesh Bhat, G. P. Shukla, Kunwar K. Singh, Deepika Gehrana

Short Communications

Evaluación de un sistema de manejo de Axonopus catarinensis en rotación basado en el remanente

53-57

de forraje no pastado (Renopa)

Daniel R. Pavetti, Marcelo A. Benvenutti, Óscar Radke, Ómar A. Cibils

Tropical Grasslands-Forrajes Tropicales (2018) Vol. 6(1):1–14 1

DOI: 10.17138/TGFT(6)1-14

Review Paper

Tropical forage legumes for environmental benefits: An overview

Leguminosas forrajeras tropicales para beneficios ambientales: Una sinopsis

RAINER SCHULTZE-KRAFT1, IDUPULAPATI M. RAO1,2, MICHAEL PETERS1, ROBERT J. CLEMENTS3,

CHANGJUN BAI4 AND GUODAO LIU4

1 International Center for Tropical Agriculture (CIAT), Cali, Colombia. www.ciat.cgiar.org

2 Presently: Plant Polymer Research Unit, National Center for Agricultural Utilization Research, ARS, USDA, Peoria,

IL, USA. www.ars.usda.gov

3 Formerly: Australian Centre for International Agricultural Research (ACIAR), Canberra, Australia. aciar.gov.au

4 Chinese Academy of Tropical Agricultural Sciences (CATAS), Haikou, Hainan, PR China. www.catas.cn

Abstract

Ruminant livestock production in the tropics, particularly when based on pastures, is frequently blamed for being detrimental to the environment, allegedly contributing to: (1) degradation and destruction of ecosystems, including degradation and loss of soil, water and biodiversity; and (2) climate change (global warming). In this paper we argue

that, rather than being detrimental, tropical forage legumes can have a positive impact on the environment, mainly due

to key attributes that characterize the Leguminosae (Fabaceae) family: (1) symbiotic nitrogen fixation; (2) high nutritive

value; (3) deep-reaching tap-root system; (4) wide taxonomic and genetic diversity; and (5) presence of particular secondary metabolites. Although there are also potential negative aspects, such as soil acidification and the risks of introduced legumes becoming invasive weeds, we submit that legumes have potential to contribute significantly to sustainable intensification of livestock production in the tropics, along with the provision of ecosystem services. To further assess, document and realize this potential, research for development needs in a range of areas are indicated.

Keywords : Biodiversity, ecosystem services, GHG emissions, land rehabilitation, soil enhancement, symbiotic nitrogen fixation.

Resumen

La producción ganadera de rumiantes en el trópico, especialmente cuando es basada en pasturas, frecuentemente es considerada como perjudicial para el medio ambiente, ya que supuestamente contribuye con: (1) la degradación y destrucción de ecosistemas, incluyendo la pérdida de suelo, agua y biodiversidad; y (2) el cambio climático

(calentamiento global). En el artículo se exponen argumentos para mostrar que, en lugar de ser perjudiciales, las leguminosas forrajeras tropicales pueden impactar positivamente en el medio ambiente, principalmente debido a sus atributos clave que son característicos de la familia de las Leguminosae (Fabaceae): (1) fijación simbiótica de nitrógeno;

(2) alto valor nutritivo; (3) sistema de raíz pivotante profundo; (4) amplia diversidad taxonómica y genética; y (5) presencia de metabolitos secundarios particulares. Aunque se deben reconocer aspectos negativos como la contribución

potencial a la acidificación del suelo y el riesgo de convertirse en malezas invasoras, concluimos que las leguminosas

forrajeras tienen un potencial significativo para contribuir a la intensificación sostenible de la producción ganadera en el trópico, junto con la prestación de servicios ecosistémicos. Sugerimos una serie de áreas donde se requiere de investigación para evaluar más a fondo, documentar y realizar este potencial.

Palabras clave : Biodiversidad, emisiones de GEI, fijación simbiótica de nitrógeno, mejoramiento del suelo, rehabilitación de tierras, servicios ecosistémicos.

___________

Correspondence: Rainer Schultze-Kraft, International Center for

Tropical Agriculture (CIAT), Apartado Aéreo 6713, Cali, Colombia.

Email: r.schultzekraft@cgiar.org

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

2 R. Schultze-Kraft, I.M. Rao, M. Peters, R.J. Clements, C. Bai and G. Liu

Introduction

Environmental issues

Feeding the world population is a major challenge for the

The main, human-induced environmental problems, as

future when one considers that in 2050 there will be an

currently perceived, are related to: natural resources,

expected >9 billion people on this planet. Consequently,

including biodiversity; and climate change.

food production must be increased and intensified (FAO

Regarding natural resources, it is generally accepted

2010). At the same time, there is growing concern about

that the major issues are: (1) ecosystem destruction and

the environmental impact of agricultural production, in

degradation; (2) soil degradation and loss; (3) water

particular of livestock (Steinfeld et al. 2006). While past

degradation and loss; and (4) biodiversity degradation and

agricultural research focused primarily on increased

loss. Obviously, these problem areas are all interrelated.

production, it is now well recognized that ecological

Regarding climate change and its major manifestations

concerns must be addressed as well if environment-

(global warming leading to modifications of rainfall regimes

friendly production strategies are to be developed and

and both flooding and drought phenomena), IPCC (2014)

sustainable intensification (SI) is to be achieved (Garnett

states that the main driver is increased anthropogenic

et al. 2013; The Montpellier Panel 2013). SI encompasses

greenhouse gas (GHG) emissions, mainly carbon dioxide

increased production from existing farmland without

(CO2), methane (CH4) and nitrous oxide (N2O).

negatively affecting the environment, and the approach

has been adopted as a policy goal for a number of national

Livestock production and the environment: Some

and international organizations working towards sustain-

background essentials

able development goals. This SI policy goal applies also

to research on tropical pastures and forages and is reflect-

When considering livestock production in the tropics and

ed, for example, in the theme of the last International

its impact on the environment, a few issues should be

Grassland Congress (New Delhi, India, November 2015):

highlighted:

Sustainable Use of Grassland Resources for Forage Pro-

 In the scientific and non-scientific communities,

duction, Biodiversity and Environmental Protection.

livestock production, including grazing, is blamed for

Two recent overview analyses of tropical forage-based

severe negative impacts on the environment (e.g.

livestock production systems vis-à-vis the environment and

Steinfeld et al. 2006; Hyner 2015). Livestock production

the need for SI concluded that such systems can have a

is estimated to contribute 14.5% of all anthropogenic

positive impact on the environment (Peters et al. 2013; Rao

GHG emissions globally (Gerber et al. 2013).

et al. 2015). In tropical production systems, the term

 The demand for animal products, especially foods derived

‘forages’ refers mostly to grasses, since adoption of legume

from livestock, is expected to increase consid-erably in the

technology in the past has been rather low (Shelton et al.

future, particularly in South, East and Southeast Asia, and

2005). We hypothesize, however, that tropical forage

to a lesser extent in Sub-Saharan Africa, as a consequence

legumes do have the potential to play a particular, positive

of increasing living standards (Rosegrant et al. 2009;

role in addressing environmental concerns.

Robinson and Pozzi 2011).

Therefore, complementing the above-mentioned over-

 In view of physical limitations to expansion of land

views and in order to contribute to the development of

area for agricultural production (both crop and

research strategies, in this paper we analyze the effects of

livestock), future production increases must come

tropical forage legumes (pasture plants for grazing or

mainly from intensification of production systems

fodder plants for cut-and-carry or browsing) on the

(The Montpellier Panel 2013).

environment. For this, we briefly: outline the main anthro-

 Ruminant livestock (e.g. cattle, buffalo, sheep, goats)

pogenic environmental issues; highlight some essentials

play an important role as they convert vegetation,

related to livestock production and the environment; and

which is unsuitable as food for humans, into high-

discuss the key attributes of forage legumes that con-

quality products for human consumption. Nonethe-

tribute to natural resource conservation and environ-

less ruminants are fed grain-based diets (such as in

mental protection with a particular emphasis on

feedlots), and this practice is in direct competition with

adaptation to and mitigation of climate change. We then

humans for that food source (Mottet et al. 2017).

examine the potential of tropical forage legumes to have

 Tropical grazing lands often occupy marginal land that

a positive impact on environmental issues and provide

is unsuitable or only marginally suitable for crop

ecosystem services.

production, because of constraints imposed by soil

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Tropical forage legumes and environment 3

physical and chemical properties, topography

3. Many legumes have a deep-reaching taproot system,

(including slopes and waterlogging) and climatic

providing access to water and nutrients in deeper soil

conditions (Rao et al. 2015). Similarly, some lands are

layers (Rao 1998; Dubeux et al. 2015), which

temporarily unsuitable for crop production due to

contributes to improved cycling of both N and P

drought or excess of water, and these areas are

(Thomas 1995; Oberson et al. 2006).

expected to increase in the tropics (Zabel et al. 2014).

4. There is an enormous organismal (taxonomic) and

Here, crop production could benefit from a crop-

genetic diversity in the Leguminosae (or Fabaceae)

forage rotation.

family with almost 20,000 species (Williams 1983;

 As far as research on tropical pastures and forages is

Lewis et al. 2005) in formerly 3, now 6 (LPWG 2017),

concerned, the literature provides almost no indication

subfamilies. This includes annuals and peren-nials,

that, in the past, environmental issues have played a

growth forms ranging from herbaceous, prostrate

major role in forage development and utilization.

species (e.g. Arachis pintoi) to vines (e.g. Centrosema

spp.), subshrubs (many Stylosanthes spp.), shrubs (e.g.

Notable exceptions are the concerns expressed by

Cratylia argentea) and trees (e.g. Leucaena spp.).

McIvor et al. (1997; 2005) and Noble et al. (2000).

Such diversity suggests that a very wide range of

production-relevant features, in terms of adaptations to

Key attributes of legumes

abiotic and biotic constraints, biomass production

potential etc., could be expected; they warrant further

The main 5 features of this plant family in general are

exploration.

summarized as follows:

5. A wide range of phytochemicals (secondary meta-

1. Legumes in the Papilionoideae subfamily and in what

bolites) occur in many species of the Leguminosae.

used to be the Mimosoideae subfamily [now the

These are often referred to as ‘antinutritional factors’

‘mimosoid

clade’

in

the

newly

defined

when legume feeding to livestock is considered

Caesalpinioideae subfamily (LPWG 2017)] and a few

(Kumar and D´Mello 1995).

taxa in the Caesalpinioideae subfamily can fix, in

These key features imply that legumes can have a

symbiosis with rhizobia ( Bradyrhizobium, Rhizobium),

significant ecological advantage over other plant families.

atmospheric nitrogen (N). Therefore they have the

However, it is also via this ecological advantage that a

potential to: (1) be N self-sufficient; and (2) increase N

legume can become a weed that threatens biodiversity

availability in the soil for associated or subsequent

and/or agricultural productivity and can also affect

crops, forage grasses and soil biota. Depending on

productivity via soil acidification (see below).

legume species, effectiveness of rhizobium strains,

nutrient supply (mainly phosphorus, potassium and the

trace element molybdenum), climatic conditions and

Tropical forage legumes and natural resources

assessment method applied, published data for

symbiotic N fixation (SNF) by tropical forage legumes

Concern 1. Ecosystem destruction and degradation

cover a wide range, e.g. 15−158 kg N/ha/yr using 15N

methodologies (Thomas 1995); a recent example is the

This concern encompasses both the destruction of natural

range of 123‒280 kg symbiotically fixed N/ha/yr in 6

ecosystems such as forests and the degradation of areas

Arachis glabrata cultivars, reported by Dubeux et al.

that have already undergone land use changes, such as

(2017a). Total input of SNF to mixed grass-legume

unproductive, mismanaged pastures. ‘Prevention is better

pasture systems can range from 98 to 135 kg N/ha/yr

than cure’ – so the initial approach to this problem should

(Boddey et al. 2015). This attribute is particularly

be taking measures to avoid ecosystem destruction and

important in production systems that depend on external

land degradation in the first place. Solving this issue does

N inputs (Douxchamps et al. 2014).

not require development of technology but rather appli-

2. Most forage legumes have high nutritive value for

cation of existing appropriate land use policies and

ruminants, mainly in terms of concentration of crude

strategies.

protein (CP) (percentage N x 6.25) but also of energy

Among them is the SI policy goal of concentrating

(Lüscher et al. 2014). This feature can be particularly

production on existing agricultural land (Garnett et al.

significant in mixtures with, or as complement to,

2013; The Montpellier Panel 2013), thereby lowering the

grasses with CP levels often below livestock

colonization pressure on natural ecosystems that should

maintenance requirements or when low-CP and low-

be considered as ecological and biodiversity reserves.

digestibility crop residues are fed.

Intensification, however, is usually closely linked to N

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

4 R. Schultze-Kraft, I.M. Rao, M. Peters, R.J. Clements, C. Bai and G. Liu

fertilization and its detrimental consequences for the

ovalifolium (‘ D. ovalifolium’) and Arachis pintoi can

environment (nitrate leaching and emission of N2O, a

control erosion, suppress weed growth and provide

potent GHG; see below).

forage. Dubeux et al. (2017b) reviewed the role of tree

Forage legumes can contribute to SI by providing N to

legumes and their benefits in warm-climate silvopastoral

the soil-plant system and high quality forage to livestock.

systems and concluded that they were a key component

By this, the productivity of land and livestock can be

for the SI of livestock systems in that climatic zone.

substantially increased in production systems with grass-

Research has shown that, once mismanaged land has

legume pastures and/or legume-only protein banks. In

become unproductive, both herbaceous (Ramesh et al.

Table 1 a number of examples in the tropics are presented.

2005) and woody legumes (Chaer et al. 2011) can be used

There is also significant potential to increase overall

successfully for rehabilitation of degraded land, including

land productivity via mixed-production systems such as

degraded cattle ranching land (Murgueitio et al. 2011).

agropastoral systems (Ayarza et al. 2007; Boddey et al.

2015), including intercropping forage legumes (Hassen et

Concern 2. Soil degradation and loss

al. 2017), and (agro) silvopastoral systems (Nair et al.

2008; Dubeux et al. 2015). Multi-purpose legumes serve

Soil degradation and loss are intimately linked to the

multiple roles, e.g. Leucaena leucocephala provides

previous concern, ecosystem destruction and degradation.

wood and forage, while Desmodium heterocarpon subsp.

The loss of top soil, where most soil organic carbon

Table 1. Effects of tropical forage legumes on liveweight gain of cattle (extracted from Rao et al. 2015).

Grass

Country/region

Climate/

Legume species

Liveweight gain

Reference

ecosystem

Grass alone

With legume

Native

Australia, Central

Dry subtropics

Stylosanthes

83 kg/an/yr

121 kg/an/yr

Shaw and

( Heteropogon

Queensland

humilis

Mannetje

contortus)

(1970)

Native

Australia,

Dry tropics

Centrosema

-183 g/an/d

489 g/an/d

McCown et al.

Northern Territory

pascuorum 1

(1986)

Urochloa

Australia,

Dry tropics

Leucaena

381 g/an/d2

723 g/an/d2

Jones et al.

mosambicensis Northern

leucocephala cv.

(1998)

Queensland

Cunningham

L. diversifolia

532 g/an/d2

Brachiaria

Venezuela,

Humid tropics

Desmodium

336 g/an/d

385 g/an/d

Chacón et al.

humidicola 3

Táchira

ovalifolium 4

(2005)

Brachiaria

Colombia, Llanos

Subhumid

Pueraria

124 kg/an/yr

174 kg/an/yr

Lascano and

decumbens 5

(savanna)

phaseoloides

Estrada (1989)

Andropogon

Colombia, Llanos

Subhumid

Stylosanthes

120 kg/an/yr

180 kg/an/yr

CIAT (1990)

gayanus

(savanna)

capitata

240 kg/ha/yr

280 kg/ha/yr

Brachiaria

Colombia, Llanos

Subhumid

Centrosema

191 g/an/d6

456 g/an/d6

Thomas and

dictyoneura3

(savanna)

acutifolium cv.

Lascano (1995)

Vichada

Stylosanthes

446 g/an/d6

capitata

Brachiaria

Brazil, Mato

Subhumid

Calopogonium

327 kg/ha/yr

385 kg/ha/yr

CNPGC (1988)

decumbens 5

Grosso do Sul

(savanna)

mucunoides

Pennisetum

Brazil, Santa

Humid

Arachis pintoi

716 g/an/d

790 g/an/d

Crestani et al.

purpureum cv.

Catarina

subtropical

(2013)

Kurumi

Brachiaria

Costa Rica,

Humid tropics

Arachis pintoi

139 kg/an/yr8

166 kg/an/yr8

Hernández et al.

brizantha 7

Guápiles

597 kg/ha/yr8

736 kg/ha/yr8

(1995)

Brachiaria

Mexico, Veracruz

Wet-dry tropics

Cratylia argentea

580 g/an/d

839 g/an/d

González-Arcia

brizantha 7

et al. (2012)

1Supplementation as ley during the main dry season; 2192 grazing days; 3Now classified as Urochloa humidicola; 4Now classified as Desmodium heterocarpon subsp. ovalifolium; 5Now classified as Urochloa decumbens; 6Means of 3 grazing cycles totalling 385 days, newly established pastures; 7Now classified as Urochloa brizantha; 8Mean of 2 stocking rates (low and high).

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Tropical forage legumes and environment 5

(SOC) and plant nutrients are concentrated (Lal 2010),

et al. 2005); or species with physiological mech-

leads not only to loss of a stratum that is crucial for plant

anisms for avoiding and/or tolerating water stress

production but also to oxidation of SOC and subsequent

(annual life cycle, narrow leaflets, leaf move-

liberation of the GHG, CO2. Since this carbon stems from

ments, tolerance of very low leaf water potentials),

recent (= not fossil) photosynthesis, it does not alter the

such as Centrosema pascuorum (Ludlow et al. 1983;

longer-term CO2 balance in the atmosphere. However, it

Clements 1990).

is lost from a key carbon sink: soil organic matter (SOM).

 Reducing sedimentation of water bodies. Sedimentation

Among the multiple possibilities (most of which are

is a major issue with devastating consequences in times

based on legume N contribution, soil-covering growth

of excessive rainfall and is, obviously, intimately linked

habit and deep root system) to contribute to the mitigation

to soil erosion by water. Consequently, the potential role

of this environmental problem, are:

of legumes consists primarily in prevention of soil

 Soil conservation by: cover legumes such as

erosion (see above). Additional potential lies in water-

Alysicarpus vaginali s, Arachis pintoi and Desmodium

shed protection through productive, N self-sufficient

‘ovalifolium’ which prevent erosion; contour-hedges

multipurpose trees.

with shrub species such as D. cinereum and Flemingia

 Enhancement of water infiltration via the potential

macrophylla; and leguminous trees such as Erythrina

amelioration effect on soil structure of legumes (see

spp. and Leucaena spp.

above).

 Rehabilitation of degraded soils by pioneering

 Using cover legumes to control weed growth in oil

legumes such as Stylosanthes spp., Macrotyloma

palm and rubber plantations as an attractive alter-

axillare and Flemingia spp., which are deep-rooted

native to the use of herbicides.

and adapted to infertile soils, with soil improvement

 Replacing N fertilizer, at least partly, by a legume.

resulting from cycling of minerals from deeper soil

This could reduce nitrate leaching and water eutroph-

layers and enhanced concentration of SOM through

ication as both groundwater contamination by nitrate

litter production (Amézquita et al. 2004; Boddey et al.

leaching and N-eutrophication of water bodies as a

2015). In the case of tannin-rich species, such as

consequence of surface runoff are recognized negative

F. macrophylla, litter has a marked impact as it

consequences of N fertilization in tropical pastures

decomposes slowly (Budelman 1988) and provides a

(Vendramini et al. 2007).

longer-lasting soil cover and slow nutrient release.

 Exploring and exploiting the potential of legumes to

Concern 4. Biodiversity degradation and loss

ameliorate compacted soil, as shown by e.g. Rochester

et al. (2001) for Lablab purpureus (among other, more

Any land use change, such as the establishment of forage

temperate grain legumes) and Lesturguez et al. (2004)

species, has profound implications for biological diversity

for Stylosanthes hamata.

(Alkemade et al. 2013) in terms of plant and animal species

 Exploring and exploiting the potential adaptation of

and ecotypes, including entomofauna and the whole soil

species to soil salinity. There seems to be some

biota in the area concerned. This is particularly true if a

potential in a few genera such as Acaciella,

monospecific grass sward is established, as is common in

Desmanthus, Neptunia and Sesbania (Cook et al.

the tropics. While this is an area of considerable knowledge

2005).

gaps, we claim that the inclusion of an N-fixing and,

subsequently, SOM-increasing legume in a mixture with

Concern 3. Water degradation and loss

a grass will mitigate the overall negative effects of such a

land-use change on biodiversity, namely entomofauna

On a global scale, water and its decreasing availability,

and soil biota (Ayarza et al. 2007). In their review which

accessibility and quality, are major concerns (Rogers et

focused on temperate conditions, Phelan et al. (2015)

al. 2006). As far as tropical pastures and forages are

reported on positive effects of legumes on the diversity

concerned, we see the role of legumes primarily in the

and abundance of pollinating insects and earthworms.

following areas:

In this context, the possible mitigating effects on

 Use of drought-adapted species, e.g. deep-rooted herbs

biodiversity loss of using mixtures of legume species

and subshrubs such as Centrosema brasilianum and

should be explored. Mixtures of herbaceous cover

Stylosanthes guianensis; shrubs and trees such as

legumes are commonly used for weed control in

Cratylia argentea and Leucaena leucocephala (Cook

Southeast Asian tree plantations, e.g. Calopogonium

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

6 R. Schultze-Kraft, I.M. Rao, M. Peters, R.J. Clements, C. Bai and G. Liu

mucunoides, C. caeruleum, Centrosema pubescens

It has been suggested that increased presence of a grass

(now classified as C. molle), Desmodium ovalifolium

reduces the problem (Scott et al. 2000).

(now classified as Desmodium heterocarpon subsp.

ovalifolium) and Pueraria phaseoloides (Jalani et al.

Tropical forage legumes and climate change

1998). Such mixtures might also improve functional

biodiversity.

Increase in GHG emissions is claimed to be the main

A related area is the role that forage legumes can play

causal agent of climate change (Adger and Brown 1994).

in combating agricultural pests through exudation of

In low-income countries, that is, in the developing world,

chemical compounds. A significant example is the

agriculture and land use changes are estimated to

increasing use of Desmodium intortum and D. uncinatum

contribute 20 and 50%, respectively, to overall GHG

as intercrops to control maize stemborer and Striga spp.

emissions (The World Bank 2010). Climate change is

in the so-called push-pull systems in East Africa (Khan et

expected to: (1) raise temperatures across the planet; and

al. 2010; icipe 2015).

(2) disturb rainfall patterns, but regional differences will

occur, resulting in increases of both drought-stricken and

Negative aspects of tropical forage legumes

waterlogged areas, and salinization of agricultural soils

(IPCC 2014; Zabel et al. 2014; Brown et al. 2015).

Two negative aspects of tropical forage legumes must be

General strategies to cope with climate change are:

recognized:

adaptation to the modified climatic conditions; and mitigating

Weed potential. The danger that an exotic legume could

GHG emissions that lead to climate change. Both are

become a serious invasive weed that threatens local

examined in relation to tropical forage legumes as follows:

biodiversity and/or affects crop production must be

considered. According to available literature, this risk

Adaptation potential

seems to be a particular concern in Australia, even to the

point that Low (1997) suggested that introduction of

We suggest that research make use of the large organismal

exotic forage germplasm should cease with the focus

(= taxonomic) and genetic diversity of tropical forage

changing to developing cultivars from native species.

legumes that is available in the world’s major germplasm

Among the factors contributing to the weed potential are

collections, e.g. particularly those held by the Australian

(Driscoll et al. 2014): region- or production system-

Pastures Genebank, CIAT (Centro Internacional de

specific lack of grazing or browsing animals;

Agricultura Tropical), Embrapa (Empresa Brasileira de

unpalatability or low palatability to livestock, due to

Pesquisa Agropecuária) and ILRI (International Live-

presence of secondary metabolites; prolific seeding; and

stock Research Institute). Collections can be screened for

presence of thorns and spines. Tropical legume species

adaptation to constraints such as high temperatures and

currently listed among the 32 land plant species of “100

tolerance of drought, waterlogging or soil salinity (Baron

of the world’s worst invasive alien species” (Lowe et al.

and Bélanger 2007). As a result of phenotypic evaluation

2004) include: Acacia mearnsii, Leucaena leucocephala,

within the naturally available diversity, promising

Mimosa pigra, Prosopis glandulosa and Pueraria

germplasm can be developed further via selection or

montana var. lobata. It is well recognized that attributes

breeding (Araújo et al. 2015).

which make a legume a useful pasture species are the

In this context, existing legume germplasm collections

same as those which allow it to become potentially a

need to be complemented by further gathering of wild

serious weed.

germplasm in the field. Collecting missions should focus

Even if a legume might not represent a risk to

on areas which experience drought or waterlogging or soil

biodiversity on a larger scale, at the pasture level soil N

salinity problems, i.e. areas where naturally occurring

accumulation following eventual legume dominance

plants can be expected to have the desired adaptations for

could lead to changes in species composition: nitro-

survival and productivity.

philous weeds can become an agroecological problem

(McIvor et al. 1996).

Mitigation potential

Soil acidification. Continuous use of legume-only or

legume-dominated swards can result in soil acidification

While a recent overview (Peters et al. 2013) concluded

as Noble et al. (1997) and Liu et al. (1999) reported for

that tropical pastures and forages in general have the

Stylosanthes species in Australia and China, respectively.

potential to play a significant role in mitigation of climate

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Tropical forage legumes and environment 7

change, the following discussion refers specifically to the

SOM under legume-only vegetation is less stable than

contribution of forage legumes.

under a grass-legume mixture (Sant-Anna et al. 2017).

Methane (CH4). Methane has 25 times greater global

Carbon dioxide (CO2). The work of Fisher et al. (1994) in

warming potential per unit mass (100-yr time horizon)

the Colombian Llanos showed that sown, deep-rooted

than CO2. In agriculture, it is generated mainly by enteric

tropical grasses can accumulate more SOC than native

fermentation, manure management and rice cultivation.

savanna, in fact, almost as much as under forest. When a

By nature ruminants produce enteric CH4 (Broucek 2014)

legume was mixed with the grass, the amount of C stored

and research is underway to determine how this might be

in the soil (0−80 cm) increased by 20% to a total of 268 t

modified. Options are either to increase the amount of

C/ha. Tarré et al. (2001) reported that, in the humid tropics

meat or milk produced per unit of CH

of Bahia, Brazil, soil C accumulation (0−100 cm soil depth)

4 emitted or to

decrease the amount of CH4 emitted per unit of feed intake

in a Brachiaria humidicola (now accepted as Urochloa

through: (1) providing high quality forage, mainly in

humidicola) -Desmodium ovalifolium (now accepted as

terms of CP concentration and digestibility; and (2)

Desmodium heterocarpon subsp. ovalifolium) pasture over

improving livestock breeds that are able to respond to

a 9-yr period was almost twice that of a B. humidicola

improved forage quality with increased productivity

pasture (1.17 vs. 0.66 t C/ha/yr). Contributions by non-

(Gerber et al. 2013).

tropical permanent pastures and perennial legumes to

In a recent meta-analysis, Lee et al. (2017) showed that

increased C accumulation in the soil are cited in the review

rising temperatures lead to decreased nutritive value of

of Jensen et al. (2012). According to these authors, the

grasses and increased CH4 emissions by ruminant

organic N provided by the legumes fosters C accumulation.

livestock, which worsens the global warming scenario.

As Smith et al. (2008) and Chaer et al. (2011) showed, trees

On the other hand, forage legumes have high nutritive

in agroforestry systems, particularly leguminous trees,

value and can contribute to lower emissions of CH4 per

have the potential to increase C accumulation in the soil

unit of livestock product or unit of feed ingested. A study

considerably, as well as accumulating C in their own

by Molina et al. (2016) of methane emissions of Lucerna

biomass, especially on degraded land.

heifers fed a Leucaena leucocephala-stargrass mixture or

On the other hand, respiration by legume roots during

grass only demonstrated the benefits of the legume in the

the energy-consuming SNF process releases substantial

diet in reducing methane emissions per unit gain. The

amounts of CO2 to the atmosphere, even more CO2 per unit

optimal situation is to have improved livestock feeding,

N than is emitted during the production of industrial N

based on high quality forage including legumes, combin-

fertilizer (Jensen et al. 2012). As these authors point out,

ed with improved livestock breeds that can more

however, in contrast to CO2 from fertilizer production, CO2

efficiently use such improved feed.

produced during SNF stems from photosynthesis, so the

In addition to this general quality-based role of forage

atmospheric CO2-concentration balance is not altered.

legumes regarding enteric CH4, another meta-analysis

The particular role of SOM merits further emphasis.

(Jayanegara et al. 2012) showed that polyphenols such as

This is the most important carbon sink and can be larger

condensed tannins, i.e. secondary metabolites that occur

than the above-ground C in a tropical rainforest (Lal

in many tropical forage legumes, decrease CH4 emissions.

2010). If soil erodes, this eventually leads to oxidation of

According to an analysis based on 22 in vivo studies,

C to CO2, which is released to the atmosphere (Olson et

ruminants fed warm-climate legumes produced less CH4

al. 2016). Therefore, perennial plants, e.g. grasses and

per kg OM intake than ruminants fed cold-climate

legumes, which provide soil cover and prevent erosion,

legumes, C3 grasses and C4 grasses (Archimède et al.

play a particularly significant role in mitigating CO2

2011). Low-molecular weight tannins, such as those in

emissions in tropical production systems. To guarantee

L. leucocephala (Molina et al. 2016), can also play a role.

this environmental benefit, vegetation/pasture manage-

It is important to ensure that tannins in the diet do not

ment must be such that there is always adequate soil

reduce protein digestibility, compromising animal intake

cover. Creeping, stoloniferous species such as

and thus its performance, which in turn will affect CH4

Desmodium ‘ovalifolium’ and Arachis pintoi that provide

emissions per unit of livestock product. Working with

a dense soil cover – while supplying N-rich litter – appear

subterranean clover ( Trifolium subterraneum) Kaur et al.

to be of particular interest. It must, however, be

(2017) showed that a plant breeding approach to reduce

mentioned that, because of the low C:N ratio of legumes,

methanogenesis has potential.

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

8 R. Schultze-Kraft, I.M. Rao, M. Peters, R.J. Clements, C. Bai and G. Liu

Nitrous oxide (N2O). Nitrous oxide has 300 times greater

Legume technology adoption and payment for ecosystem

global warming potential per unit mass (100-yr time

services

horizon) than CO2. Its production by soil microorganisms

during nitrification and denitrification processes is very

In their review paper, which examined the role of forage

much related to the use of N fertilizers in agriculture

legumes in general (though they focused primarily on

(Subbarao et al. 2013). In their meta-analysis, Jensen et

temperate zones), Phelan et al. (2015) reported a low and

al. (2012) concluded that there is a tendency for lower

even declining use of forage legumes. We must recognize

N

that in the tropics adoption of legume-based technologies

2O production from soil under legumes than from

systems based on industrial N fertilizer, depending on the

has, in general, been disappointing – in spite of many success

amount of N fertilizer applied. This seems to be an area

stories with tropical forage legumes worldwide (see the 33

of considerable knowledge gaps in relation to tropical

contributions in Tropical Grasslands Vol. 39, No. 4, 2005;

forage legumes.

goo.gl/Qf5VJu). The reasons were analyzed by Shelton et al.

(2005) and include a number of issues that should be taken

In view of the recent detection of biological nitrification

into account when planning R&D programs promoting the

inhibition (BNI) in some tropical forage grasses,

use of tropical forage legumes. A particularly important

particularly Brachiaria (now Urochloa) humidicola

issue is the organization of efficient seed production

(Subbarao et al. 2009; 2017), the challenge is to determine

systems. The lack of seed availability is often cited as a

whether such a mechanism might also exist in tropical

key reason for adoption failure and the resulting vicious

forage legumes. It might then be possible to exploit the

circle (lack of robust demand – lack of interest of the

synergy between SNF and BNI to the benefit of both

private seed production sector – lack of seed production

agriculture and the environment. Due to BNI, symbiotically

and availability – lack of adoption) needs to be broken.

fixed N might be available for longer periods and less prone

Successful results have been achieved with contracting

to loss by nitrate leaching and N2O production.

farmers for forage legume seed production and farmer to

farmer seed sales, e.g. in Thailand, India and Bolivia. For

Discussion and Conclusions

large-scale adoption it will be essential to develop

systems which ensure high seed quality and are

Ecosystem services

commercially viable (Shelton et al. 2005).

We doubt that an eventual recognition of the ‘new’

In the preceding sections, we showed that tropical forage

ecosystem services role of legumes will modify farmers’

legumes have considerable potential to increase

lack of enthusiasm for legumes to a marked extent.

productivity of forage-based livestock systems, while

Although promotional and educational activities, along

providing benefits to the environment. The environmental

with results from further research involving farmer

benefits, subsumed under ‘ecosystem services’, comprise

participation, might be helpful, we expect that constraints

positive effects on: soil conservation and soil chemical,

imposed by the need for management skills and

physical and biological properties; water balance;

investments will remain, unless attractive economic

mitigation of global warming and of groundwater

incentives are offered to farmers (White et al. 2013). Such

contamination; saving of fossil energy; functional

incentives should not be restricted to legume-based

technologies but should extend to all tropical forage

biodiversity (soil, entomofauna); and rehabilitation of

technologies which provide environmental services. We

degraded land. The combination of these features makes

suggest that schemes of payment for ecosystem services

tropical forage legumes particularly valuable at all levels

(PES) (Pagiola et al. 2004; Van Noordwijk and Leimona

of the system because of their interaction with plants, soil,

2010), applicable to both smallholders and large livestock

animals and the atmosphere. This environmental role

producers, be explored, developed and implemented.

could be considered as a ‘new’ important dimension of

tropical forage legumes.

The need for life cycle assessments

A crucial aspect, however, is: During past decades the

beneficial role of tropical forage legumes was promoted

Inputs of N are necessary in all pastures if livestock

with the sole focus on livestock production and soil

productivity is to be increased, such as within the concept

fertility; what must be done to have legume-based

of SI. Basically, there are 2 options: (1) planting legumes

technologies more readily adopted by farmers now that

with SNF capability in mixtures with grasses; and (2)

general environmental benefits are recognized?

applying industrial N fertilizers to grass-only swards.

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Tropical forage legumes and environment 9

Greenhouse gas emissions from both approaches should

 assessment of the impact of promising legume species

be measured. We suggest that full life cycle assessments

on rumen methanogenesis;

for tropical pastures addressing the whole carbon

 identification of tanniniferous legumes which con-

footprint (Eshel et al. 2014) should be performed. In their

currently provide high quality forage in terms of

temperate climate-focused review, Phelan et al. (2015)

digestibility in the rumen and reduced methane

reported that CO2-equivalent emissions for Trifolium

emission intensity;

repens-grass pastures were 11‒23% lower than for N-

 identification of anti-methanogenic compounds other

fertilized grass. Such life cycle assessments must include

than tannins in legume forage;

the need for fossil energy and any benefits to any

 assessment of the BNI potential of forage legumes;

subsequent crop in a rotational system (de Vries and de

 development of methodologies for payment for

Boer 2010; Jensen et al. 2012).

ecosystem services;

 optimization of SNF via enhanced exploration and

Research needs

exploitation of rhizobia diversity; and

 targeted collection of wild legume germplasm for

The suboptimal adoption of forage legume technologies

development of varieties with improved adaptation to

in the past – when only forage dry matter and/or livestock

climate variability and change.

production was considered – has led to a substantial

decrease in research on tropical forage legumes during the

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(Received for publication 23 October 2017; accepted 12 January 2018; published 31 January 2018)

© 2018

Tropical Grasslands-Forrajes Tropicales is an open-access journal published by International Center for Tropical Agriculture (CIAT). This work is licensed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Tropical Grasslands-Forrajes Tropicales (2018) Vol. 6(1):15–25 15

DOI: 10.17138/TGFT(6)15-25

Research Paper

Soil attributes of a silvopastoral system in Pernambuco Forest Zone

Atributos del suelo en un sistema silvopastoril en la “Zona da Mata”,

Pernambuco, Brasil

HUGO N.B. LIMA1, JOSÉ C.B. DUBEUX JR.2, MÉRCIA V.F. SANTOS1, ALEXANDRE C.L. MELLO1, MÁRIO

A. LIRA2,3 AND MÁRCIO V. CUNHA1

1 Departamento de Zootecnia, Universidade Federal Rural de Pernambuco, Recife, PE, Brazil. www.ufrpe.br

2 University of Florida, North Florida Research and Education Center, Marianna, FL, USA. nfrec.ifas.ufl.edu

3 Instituto Agrônomico de Pernambuco, Recife, PE, Brazil. www.ipa.br

Abstract

This research evaluated soil properties in a silvopastoral system using double rows of tree legumes. Treatments were

signalgrass ( Brachiaria decumbens) in monoculture or in consortium with sabiá ( Mimosa caesalpiniifolia) or gliricidia ( Gliricidia sepium). Treatments were arranged in a complete randomized block design, with 4 replications. Response

variables included chemical characteristics and physical attributes of the soil. Silvopastoral systems had greater (P<0.001) soil exchangeable Ca (gliricidia = 3.2 and sabiá = 3.0 mmolc/dm3) than signalgrass monoculture (2.0

mmolc/dm3). Water infiltration rate was greater within the tree legume double rows (366 mm/h) than in signalgrass (162

mm/h) (P = 0.02). However, soil moisture was greater in signalgrass pastures (15.9%) (P = 0.0020) than in silvopastures

(14.9 and 14.8%), where soil moisture levels increased as distance from the tree rows increased. Conversely, the light

fraction of soil organic matter was greater within the tree legume double rows than in the grassed area (P = 0.0019).

Long-term studies are needed to determine if these benefits accumulate further and the productivity benefits which result.

Keywords : Fertility, legumes, soil physics, trees.

Resumen

Entre enero 2012 y diciembre 2013 en Itambé, Pernambuco, Brasil, se evaluaron algunas propiedades físicas y químicas

del suelo en un sistema silvopastoril, utilizando filas dobles de leguminosas arbóreas. Los tratamientos consistieron en

Brachiaria decumbens sola o en asociación con sabiá ( Mimosa caesalpiniifolia) o gliricidia ( Gliricidia sepium) en un diseño de bloques completos al azar, con 4 repeticiones. Los sistemas silvopastoriles presentaron mayor contenido (P<0.001) de calcio intercambiable (gliricidia = 3.2 y sabiá = 3.0 mmolc/dm3) comparados con la gramínea sola (2.0

mmolc/dm3). La tasa de infiltración de agua fue mayor en el suelo dentro de las filas dobles de los árboles leguminosos

(366 mm/h) en comparación con la gramínea sola (162 mm/h) (P = 0.02). No obstante, la humedad fue más alta en el

suelo con gramínea (15.9%) (P = 0.0020) comparada con los sistemas silvopastoriles (14.9 y 14.8%, respectivamente

para sabiá y gliricidia). La humedad en el suelo aumentó con la distancia a partir de la línea de árboles. Por el contrario, la fracción ligera de la materia orgánica del suelo fue mayor (P = 0.0019) dentro de las filas dobles de árboles (0.071

mg/kg) comparada con el suelo fuera de la línea de árboles. Se requieren estudios a largo plazo para determinar si estos

beneficios continuan acumulándose y si resultan en mayor productividad.

Palabras clave: Árboles, fertilidad, física del suelo, leguminosas.

___________

Correspondence: J.C. Batista Dubeux Jr., University of Florida, North

Florida Research and Education Center, 3925 Highway 71, Marianna,

FL 32446, USA.

Email: dubeux@ufl.edu

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

16 H.N.B. Lima, J.C.B. Dubeux Jr., M.V.F. Santos, A.C.L. Mello, M.A. Lira and M.V. Cunha

Introduction

Given the economic and environmental importance of

these systems, this study aimed to evaluate the chemical

Good soil physical characteristics are essential to ensure

composition and physical properties of soils in

satisfactory crop and pasture productivity. Pasture soils tend

signalgrass pastures [ Brachiaria decumbens Stapf; now:

to have greater soil density than preserved vegetation soil,

Urochloa decumbens (Stapf) R.D. Webster], in associa-

presumably due to trampling by animals (Vitorino 1986),

tion with tree legumes in the coastal region (“Zona da

which can also have an impact on the water infiltration rate

Mata”) of Pernambuco State, Brazil.

and soil moisture holding capacity, both of which have

significant effects on pasture productivity. The amount of

Materials and Methods

water that infiltrates and flows over the ground is directly

related to soil physical properties such as density, and the

The research was conducted at the Experimental Station

existing vegetative cover (Lanzanova et al. 2007).

of the Agronomic Institute of Pernambuco (IPA), located

Soil organic matter (SOM) has a major influence on

in Itambé, Pernambuco, Brazil. Average annual rainfall is

ecosystem productivity because it affects chemical and

1,300 mm, and average annual temperature is 25 °C

physical characteristics of soils. Since SOM is the net

(CPRH 2003). The climate is sub-humid, the topography

result of soil processes occurring in the long term, it is

is undulating and the soil of the study area is classified as

difficult to detect early changes if analyzing total SOM

Ultisol (red-yellow dystrophic Argissol according to the

(Haggerty and Gorelick 1998). The light fraction of the

Brazilian Soil Classification or Paleudult or Ferric

SOM is formed by plant and animal residues in the early

Luvisol according to FAO World Reference Base)

stages of decomposition. It represents recent changes in

(Jacomine et al. 1972; Embrapa 2006). Initial soil

chemical characteristics of the experimental area were:

land management and can detect early changes in SOM

pH in water (1:2.5) 5.5; P (Mehlich-I) 2.2 mg/dm3; K 1.3

dynamics (Jinbo et al. 2007; Rangel and Silva 2007).

mmolc/dm3; Ca 27 mmolc/dm3; Mg 20 mmolc/dm3; Na

Increases in ecosystem primary productivity lead to

1.4 mmolc/dm3; Al 2.7 mmolc/dm3; H+Al 61.7 mmolc/

increasing residue deposition, both above- and below-

dm3; and SOM 44.2 g/kg. Average monthly rainfall for

ground.

the experimental years is shown in Figure 1.

Silvopastoral systems improve soil physical attributes

Three treatments were tested in a complete

such as soil aggregates, soil density and water infiltration

randomized block design with 4 replications. Treatments

rates (Carvalho et al. 2004). Litter deposition from tree

included: 1) sabiá with signalgrass; 2) gliricidia with

foliage is a major pathway for recycling of nutrients in a

signalgrass; and 3) signalgrass monoculture. Each

silvopastoral system (Apolinário et al. 2016). Limited

experimental unit measured 660 m2 (33 x 20 m). Tree

nitrogen (N) availability in warm-climate grasslands is

legumes (sabiá and gliricidia) were established in 2008 in

one of the major limiting factors to increases in

double rows spaced at 10.0 m (between double rows) x

productivity (Vendramini et al. 2014), and N addition via

1.0 m (between rows) x 0.5 m (within rows). Each plot

litter represents a significant input and might result in

contained 3 double rows. The signalgrass was growing

greater ecosystem primary productivity. Tree legumes

throughout the area of each plot, but reduced growth

such as sabiá ( Mimosa caesalpiniifolia Benth.) and

occurred between the individual tree legume rows that

gliricidia [ Gliricidia sepium (Jacq.) Kunth] can be used in

formed the double rows (“within tree legume double

silvopastoral systems (Souza and Espíndola 2000; Vieira

rows” from here on), especially under sabiá trees.

et al. 2005; Apolinário et al. 2016; Costa et al. 2016).

Livestock were introduced to the paddocks when the

Besides biological N2 fixation, litter deposition and

sward height reached 60 cm, and remained until the

decomposition are important sources of nutrients to be

stubble height of the grass was reduced to 10‒15 cm.

reused by the system (Apolinário et al. 2016).

Soils from tree legume paddocks were sampled in

Tree legumes can provide extra alternative income

September 2012 in order to determine the chemical

through the sale of fencing posts and firewood

composition. Samples were collected in 2 transect lines

(Apolinário et al. 2015). Incorporating tree legumes in

perpendicular to the tree rows. Along each transect, 5

silvopastoral systems can also provide other ecosystem

different points were sampled (0, 1, 2, 3 and 4 m distance

services including the maintenance of biodiversity,

from each tree double row) giving 30 samples per plot

improvement of water and nutrient flow, enhancement of

(Figure 2). Paddocks with signalgrass monoculture were

soil quality, reduction of soil erosion, improvement of C

sampled randomly at 5 sites. All soil samples were taken

storage and provision of green areas for urban society

from the 0‒20 cm soil layer. Soil samples to determine

(Kemp and Michalk 2005).

bulk density and soil gravimetric moisture were collected

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Soils in a silvopastoral system 17

300

250

200

150

mm

100

50

0

Month / Year

Figure 1. Rainfall (monthly averages) in the experimental area during the research period. Source: Meteorological data collected at the experimental site.

in May 2013, using the same sampling protocol (per-

were macerated and sieved through a 0.5 mm sieve, and

pendicular transects) described to collect the soil fertility

then put into a 0.053 mm sieve and washed in running

samples, and the same soil depth. Undisturbed soil cores

water. The retained material was then transferred to

were collected using volumetric rings. Samples were

containers filled with water, where it remained undisturbed

dried in an oven at 105 °C for 24 hours, following

for 24 h for density separation (heavy and light fraction).

methodology described by Embrapa (1979).

The supernatant (floating) material was retrieved in 0.053

Light fraction of SOM was determined by weighing

mm mesh, dried at 65 °C for 72 h, and weighed on a

50 g of soil (samples collected for fertility analyses), which

precision scale (Correia et al. 2015).

Figure 2. Location of soil sampling points relative to tree legume rows in the silvopasture treatments.

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

18 H.N.B. Lima, J.C.B. Dubeux Jr., M.V.F. Santos, A.C.L. Mello, M.A. Lira and M.V. Cunha

Water infiltration rate (WIR) was determined in

and soil exchangeable Na was greater in the signalgrass-

January 2013. Infiltrometers made of concentric rings

sabiá pasture than in the other pastures (Table 1). When

(Bouwer 1986) were placed at 2 specific points in each

com-paring the sampling points in relation to the distance

tree legume paddock: 1) within tree legume double rows

from the rows of legumes, there was no significant effect

(sampling point 1); 2) in the middle of the grassed area

for the response variables evaluated, except for pH (Figure

(sampling point 5). A total of 48 samples were collected

3), where values increased exponentially as distance from

(2 replicates for each sample location within each

the legume rows increased, with a peak at 3 m.

silvopastoral system, and 4 samples for each signal-grass

plot). Water infiltration rate was determined when the rate

Water infiltration rate

was constant, using the following equation:

Water infiltration rate was higher within the tree legume

WIR (mm/min) = L2 - L1 (mm) / time (min)

double rows of gliricidia and sabiá (356 and 366 mm/h,

where: L2 is water at the beginning of the measurement

respectively; Figure 4) than in the signalgrass mono-

and L1 is the remaining water in the tube after the time

culture (162 mm/h) and in the grassed area of the signal-

spent measuring.

grass-sabiá (128 mm/h) treatment.

Soil attributes were analyzed using PROC MIXED

(SAS 2007). A complete randomized block design was

Gravimetric moisture

used to compare signalgrass monoculture with the

silvopastoral systems. When transects were analyzed, the

Soil moisture (Table 2) levels were higher (P<0.05) in the

transect points were considered split-plot and the main

signalgrass monoculture than in the mixed pastures; in the

plot the vegetation cover, with both being fixed effects. In

mixed pastures soil moisture increased as distance from

all analyses, blocks were considered a random effect.

the tree rows increased (P<0.05; Table 3).

Significance was declared at 5% probability. LSMEANS

Soil density was not affected by type of pasture

were compared using the PDIFF procedure and adjusted

(P = 0.58) (Table 2), but in the mixed pastures soil density

Tukey test.

increased as distance from the tree rows increased

(P<0.05; Table 3).

Results

Light fraction of soil organic matter

Soil fertility

Light fraction of SOM was unaffected by pasture type

While soil chemical composition was affected by

(P = 0.22), but within the silvopastoral treatments, light

vegetation cover (Table 1), levels of most nutrients were

fraction of SOM was greater in the sabiá treatment than

similar in all treatments (P>0.05). Soil pH was greater in

under gliricidia (64 vs.45 mg/kg, respectively; P = 0.002)

the signalgrass monoculture than in the 2 grass-legume

(Table 4). The light fraction of SOM was greater under

tree pastures. Soil exchangeable Ca was greater in the

the trees than in the grass area (71 vs. 50 mg/kg,

grass-legume tree pastures than in the grass-only pasture,

respectively; Table 3).

Table 1. Soil chemical analyses (0‒20 cm layer) in signalgrass, signalgrass-gliricidia and signalgrass-sabiá pastures.

Treatment

pH

P

K

Mg

Ca

Na

Al

H + Al

C

OM

(water – 1:2.5)

(mg/dm³)

(mmolc/dm³)

(g/kg)

Signalgrass

5.8 a

1.6 a

1.4 a

2.0 a

2.0 b

0.1 b

0.3 a

5.6 a

22.0 a

48.5 a

Gliricidia

5.4 b

2.5 a

1.7 a

2.0 a

3.2 a

0.1 b

0.3 a

6.5 a

29.3 a

43.4 a

Sabiá

5.4 b

2.5 a

1.7 a

1.9 a

3.0 a

0.3 a

0.3 a

6.4 a

23.6 a

40.7 a

Probability

0.02

0.26

0.17

0.87

0.001

0.02

0.91

0.15

0.23

0.71

CV (%)

3

38

85

14

12

67

51

10

23

30

Values followed by the same letter within columns do not differ by Duncan’s test (P>0.05). OM = organic matter.

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Soils in a silvopastoral system 19

5.5

Table 2. Soil moisture and density (0‒20 cm layer) in signal-

) 5.45

grass monoculture, signalgrass-gliricidia and signalgrass-sabiá

5.:2 5.4

pastures.

1

y = -0.0264x2 + 0.1667x + 5.2071

r 5.35

tea 5.3

Treatment

Moisture (%)

Density (g/cm3)

(w 5.25

Signalgrass

15.9 a

1.21 a

Hp 5.2

Gliricidia

14.9 b

1.22 a

5.15

Sabiá

14.8 b

1.19 a

0

1

2

3

4

Probability

0.002

0.74

Distance (m) from tree legume rows

CV (%)

3.19

4.7

Figure 3. Soil pH relative to the distance from tree legume rows

Values followed by the same letter within columns do not differ

in signalgrass-gliricidia and signalgrass-sabiá pastures.

by Duncan’s test (P<0.05).

Grassed area in signalgrass-sabiá pasture (sampling point 5)

Signalgrass monoculture

Grassed area in signalgrass-gliricidia pasture (sampling point 5)

WIR (mm/h)

Within gliricidia double rows (sampling point 1)

Within sabiá double rows (sampling point 1)

0

100

200

300

400

500

Figure 4. Water infiltration rate (mm/h) in signalgrass monoculture and grassed areas in signalgrass-gliricidia and signalgrass-sabiá pastures, and within gliricidia and sabiá double rows in the mixed pastures. The bars represent the standard error.

Table 3. Effect of distance from tree legume rows on soil moisture, soil density and soil organic matter (SOM) light fraction (0‒20

cm layer) in signalgrass-gliricidia and signalgrass-sabiá pastures.

Distance (m) from tree rows

Soil moisture (%)

Soil density (g/cm3)

SOM light fraction (g/kg)

0

14.5 b

1.18 b

0.071 a

1

14.1 b

1.19 b

0.051 b

2

15.2 ab

1.19 b

0.056 b

3

14.8 ab

1.22 ab

0.052 b

4

15.5 a

1.24 a

0.042 b

Probability

0.04

0.07

0.02

CV (%)

9.6

4.0

32.5

Values followed by the same letter within columns do not differ by Duncan’s test (P>0.05).

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

20 H.N.B. Lima, J.C.B. Dubeux Jr., M.V.F. Santos, A.C.L. Mello, M.A. Lira and M.V. Cunha

Table 4. Soil organic matter (SOM) light fraction (0‒20 cm

development of the trees, increase in litter deposition and

layer) in signalgrass-gliricidia and signalgrass-sabiá pastures.

accumulation of animal waste, provided that the system is

appropriately managed (Balbino et al. 2012; Padovan and

Treatment

SOM light fraction (g/kg)

Pereira 2012; Loss et al. 2014).

Gliricidia

0.045 b

Sabiá

0.064 a

Water infiltration rate

Probability

0.002

CV (%)

32.4

Greater WIR in the signalgrass area in consortium with

Values followed by the same letter within columns do not differ

by Duncan’s test (P>0.05).

gliricidia might be due to the fact that this legume has a

deeper root system, providing advantages such as

increased water absorption and greater efficiency in the

Discussion

search for nutrients, resulting in its high performance as

fodder for livestock (Abdulrazak et al. 1997; Ondiek et al.

This study has provided some interesting results on

1999; Juma et al. 2006). A more specific study of the root

changes in soil parameters when tree legumes are

systems of gliricidia and sabiá is necessary to better

introduced into a pure grass pasture. They contribute to

understand the influence of root properties (length, depth

our knowledge of how the legumes alter the soils in

and density) on WIR.

conjunction with an associated grass.

Silvopastoral systems allow increases in SOM because

of greater litter deposition from trees, and Bell et al.

Soil fertility

(2011) indicated that greater litter deposition increases

soil macroporosity, contributing to improved water

As in our study, Carvalho et al. (2003) reported increased

infiltration and aeration. Moisture, biological activity and

soil exchangeable Ca in silvopastoral systems 5 years after

vegetation cover can also influence soil responses, such

establishment, and attributed this increase to the greater

as the WIR (Carduro and Dorfman 1988). Dunger et al.

accumulation of litter produced by the trees. Similarly,

(2005) reported that silvopastoral systems provide a

Camarão et al. (1990) suggested that the increase in soil

favorable microclimate to increase soil microfauna,

exchangeable Ca in silvopastoral systems might be

which tend to seek shaded and humid habitats. An

explained by the increased above- and below-ground litter

increase of Coleoptera beetles in association with the

deposition. Xavier et al. (2003) also observed an increase

introduction of legumes from the genus Mimosa in

in soil exchangeable Ca in signalgrass- Acacia mangium

pastures has been reported by Dias et al. (2007). These

pasture compared with pure signalgrass.

beetles dig underground galleries in order to nest, thus

The reduction in soil pH in the mixed pastures recorded

providing the opportunity for greater water infiltration

in our study is in contrast with the findings of Oliveira et

(Miranda et al. 1998).

al. (2000), Andrade et al. (2002), Xavier et al. (2003) and Increased height and density of tree legumes in the

Dias et al. (2006), where soil pH was not affected by the

experimental area reduced the transit of grazing cattle

introduction of trees. Dias et al. (2006) also studied soil

through the rows, which might explain the lower soil

chemical composition of grass-tree legume pastures in

density at these points (Table 3). The WIR was greater

relation to the distance from the tree trunk and found

along tree legume rows as compared with the grazed area

variations in soil pH and levels of P, K, Ca and Mg tending

under the effects of treading by animals, as indicated with

to increase or decrease, depending on the legume species,

changes in soil density. These data corroborate those of

planting density and biomass production.

Lanzanova et al. (2007), who studied the effects of

In silvopastoral systems, most litter deposition occurs

grazing on water infiltration rates in soils, finding greater

near the tree trunks (Silva et al. 2013), which might

WIR values in ungrazed areas and decreasing values as

influence the reduction of soil pH. Greater litter

grazing became more intense. In our research, the

accumulation leads to greater amounts of litter nutrients

increases in soil density as distance from tree legumes

being mineralized. As a result, more leaching of ex-

increased (Table 3) was reflected in decreases in WIR.

changeable bases due to release of anions from OM might

Bertol et al. (2001) showed that heavy clay soils have a

occur (Balbinot et al. 2010). However, Pavan et al. (1986)

low percentage of the pore volume occupied by air, which

obtained an increase in soil pH in an area with greater

leads to greater rates of runoff water, lower retention of

litter deposition. Several studies on silvopastoral systems

water and consequently lower infiltration capacity.

indicated that the benefits brought by the trees to soil

Prevedello (1996) also pointed out that the reduction in

fertility of the pastures tend to increase over time with

WIR with time can be influenced by factors that operate

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Soils in a silvopastoral system 21

on the soil surface, such as surface sealing due to the

agrosilvopasture (combination of trees, crops and

impact of raindrops, which may be reduced by the canopy

livestock, grown on a particular site) and intensive

of tree legumes. Roots of tree legumes in the silvopastoral

cultivation. Perin et al. (2000) also observed greater soil

systems used in this experiment might favor soil physical

moisture when soil was covered with a thick litter layer of

aspects, maintaining and improving soil structure and

herbaceous legumes.

increasing WIR (Hernández 1998).

The increase in soil moisture as distance from the tree

Excretion of organic acids and inorganic compounds

legume rows increased meant that grasses growing in the

(e.g. P and K) by roots can influence soil characteristics,

middle of the grass strips suffered reduced competition

as they allow for increased dissolution of mineral

for soil moisture from the trees, while still having some

substances and contribute to the development of

shade to assist retention of soil moisture (Table 3). Near

rhizosphere microorganisms (Cintra et al. 1999). Roots

tree rows, there was reduced soil cover because of greater

can also favor SOM accumulation, as Lehmann and Zech

competition for resources between herbaceous and woody

(1998) found that the litter produced by the renewal of

vegetation.

roots adds about 20‒50% of the total root biomass to the

SOM pool, while only 10‒20% of litter arising from the

Soil density

aerial parts is transformed into SOM (Schroth et al. 1999).

Since roots are more recalcitrant than leaves and stems, a

Average soil density was 1.2 g/cm3, which is adequate for

greater proportion of original root biomass ends up in the

root development (Alvarenga et al. 1996; Corsini and

SOM pool than leaves and stems.

Ferraudo 1999). According to Argenton et al. (2005),

characterization of soil density depends on its textural

Gravimetric moisture

class and Rosenberg (1964) and Cintra and Mielniczuk

(1983) suggest that each soil type has a critical density,

The greater soil moisture in signalgrass monoculture was

which can reduce or even prevent root development.

probably due to the competition by different species for

Reichert et al. (2003) showed that 1.4 g/cm3 is considered

water. Legumes are less efficient in water usage than C4

the critical soil density for satisfactory growth of the root

grasses. On average, legumes use 800 kg of water to

system of plants in clay soils, but Reinert et al. (2008)

produce 1 kg of dry matter, while C4 plants use 300 kg of

indicated a greater soil density (1.85 g/cm3) as critical for

water to produce the same amount of DM (Taiz and

legumes and other vegetables in clayey soils.

Zeiger 2004; Marenco and Lopes 2009). Plant species

The lower soil density near the trees (Table 3) can be

have a marked influence on water availability in

attributed to the existence of microfauna near the trees

silvopastoral systems and Vanzela and Santos (2013)

(Miranda et al. 1998; Dunger et al. 2005; Dias et al. 2007)

highlighted that the use of eucalypts in silvopastoral

as well as a greater SOM accumulation between trees,

systems increased competition for water and nutrients

increasing the amount of soil aggregates. Iori et al. (2012)

between the trees and the associated grass.

studied soil density and soil moisture in degraded

Andrade and Valentim (1999) showed that shading is

pastures, banana cultivation, a silvopastoral system and

a positive factor in maintaining soil moisture, resulting in

preserved forest. They found greater soil moisture in less

satisfactory forage development in silvopastoral systems.

dense soil, which can be correlated with the shading

In natural shading conditions, however, trees also

potential and greater SOM in these areas. Beltrame et al.

compete with one another and the grass for light, water

(1981) stated that soil moisture affects the cohesion

and nutrients. Therefore, the water requirements of the

between soil particles, with increases in aggregation when

tree legumes might have contributed to reduced soil

soil moisture is limited, which hinders their separation by

moisture near the trees in the current research.

external forces (Silveira et al. 2010).

Another aspect that should be highlighted is the fact

that, during the collection period, the grass monoculture

Light fraction of soil organic matter

was approximately 60 cm tall, which provided 100%

ground cover, helping to maintain soil moisture. In the

While vegetation cover did not affect the light fraction of

silvopastoral systems, tall trees with dense canopies might

SOM (P = 0.22), in the mixed pastures sabiá presented

have compromised production of signalgrass, which has

greater values of SOM than gliricidia (Table 4). Chan et

only moderate shade tolerance and might suffer

al. (2002) and Zinn et al. (2005) observed that SOM

production loss due to shading (Schreiner 1987). In

stocks are directly related to residue inputs, their rate of

contrast to this, Aguiar et al. (2006) recorded greater soil

decomposition and SOM fractionation. They pointed out

moisture in silvopastoral systems compared with

that the replacement of conventional farming systems

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

22 H.N.B. Lima, J.C.B. Dubeux Jr., M.V.F. Santos, A.C.L. Mello, M.A. Lira and M.V. Cunha

with improved systems, such as silvopastures, changes

sistemas agroflorestais no município de Sobral, CE. Revista

the dynamics of litter accumulation and litter

Ciência Agronômica 37:270–278. goo.gl/1MSAV5

decomposition rate, and consequently generates greater

Alvarenga RC; Costa LM; Moura Filho W; Regazzi AJ. 1996.

increases in the light fraction of SOM. Similarly, Maia et

Crescimento de raízes de leguminosas em camadas de solo

al. (2008) showed greater amounts of light fraction of

compactadas artificialmente. Revista Brasileira de Ciência

do Solo 20:319–326. goo.gl/vtyHS3

SOM in silvopastoral systems (38.2 g/dm3) than in

Andrade CMS; Valentim JF. 1999. Adaptação, produtividade e

conventional tillage (28.4 g/dm3), because of greater litter

persistência de Arachis pintoi submetido a diferentes níveis

input from trees. The amount of light fraction in the

de sombreamento. Revista Brasileira de Zootecnia 28:439–

system is directly related to the litter deposited on the soil.

445. DOI: 10.1590/S1516-35981999000300001

Light fraction of SOM is composed of litter and organic

Andrade CMS de; Valentim JF; Carneiro JC. 2002. Árvores de

matter in intermediate stages of decomposition (Souza et

baginha ( Stryphnodendron guianense (Aubl.) Benth.) em

al. 2006) and its level at any given time is the net balance

ecossistemas de pastagens cultivadas na Amazônia

between its deposition and decomposition (Fraga 2002).

Ocidental. Revista Brasileira de Zootecnia 31:574–582.

Phenolic substances found in plants often influence

DOI: 10.1590/S1516-35982002000300006

litter decomposition rate and, consequently, nutrient

Apolinário VXO; Dubeux Jr. JCB; Lira MA; Ferreira RLC;

cycling, affecting the composition and activity of

Mello ACL; Santos MVF; Sampaio EVSB; Muir JP. 2015.

Tree legumes provide marketable wood and add nitrogen in

decomposing communities of the system (Hättenschwiler

warm-climate silvopasture systems. Agronomy Journal

and Vitousek 2000). Among these substances, flavonoids

107:1915–1921. DOI: 10.2134/agronj14.0624

are characterized by their recalcitrance, with condensed

Apolinário VXO; Dubeux Jr. JCB; Lira MA; Sampaio EVSB;

tannin (CT) concentration usually correlating with low

Amorim SO; Silva NGM; Muir JP. 2016. Arboreal legume

decomposition rates (Burhenne et al. 2013). Nozella

litter nutrient contribution to a tropical silvopasture.

(2001) found high levels of condensed tannins (near 6.9

Agronomy Journal 108:2478–2484. DOI: 10.2134/

g/kg DM in gliricidia), while Balogun et al. (1998)

agronj2016.02.0120

determined mean values of 0.8%. Beelen (2002), however,

Argenton J; Albuquerque JA; Bayer C; Wildner LP. 2005.

showed greater values in sabiá, reaching up to 20.1%.

Comportamento de atributos relacionados com a forma da

Greater CT concentration in sabiá might explain the

estrutura de Latossolo Vermelho sob sistemas de preparo e

greater light fraction of SOM observed in the silvopasture

plantas de cobertura. Revista Brasileira de Ciência do Solo

29:425–435. DOI: 10.1590/S0100-06832005000300013

with this species, compared with the one with gliricidia.

Balbino LC; Cordeiro LAM; Oliveira P; Kluthcouski J;

Oliveira P; Galerani PR; Vilela L. 2012. Agricultura

Conclusions

sustentável por meio da integração lavoura-pecuária-

floresta (iLPF). Informações Agronômicas 138:1–18.

This study has shown that incorporation of tree legumes in

goo.gl/WQpUKk

rows within a signalgrass pasture can improve soil

Balbinot E; Carneiro JGA; Barroso DG; Paulino GM;

chemical composition over time as well as increasing WIR

Lamônica KB. 2010. Crescimento inicial e fertilidade do

in the soil, and the concentration of light fraction SOM near

solo em plantios puros e consorciados de Mimosa

the trees. These findings indicate that silvopastoral systems

caesalpiniifolia Benth. Scientia Forestalis 38:27–37.

using tree legumes can potentially serve as greater C sinks

goo.gl/nvuLgd

than pure grass pastures as well as providing other services

Balogun RO; Jones RJ; Holmes JHG. 1998. Digestibility of

to farmers. However, long-term results coupled with life

some tropical browse species varying in tannin content.

Animal Feed Science and Technology 76:77–88. DOI:

cycle assessments are necessary to determine what

10.1016/s0377-8401(98)00210-7

productivity increases will result.

Beelen PMG. 2002. Taninos condensados de leguminosas

nativas do semi-árido nordestino. Ph.D. Thesis. Universidade

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© 2018

Tropical Grasslands-Forrajes Tropicales is an open-access journal published by International Center for Tropical Agriculture (CIAT). This work is licensed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Tropical Grasslands-Forrajes Tropicales (2018) Vol. 6(1):26–33 26

DOI: 10.17138/TGFT(6)26-33

Research Paper

Germination of tropical forage seeds stored for six years in ambient

and controlled temperature and humidity conditions in Thailand

Germinación de semilla de forrajeras tropicales durante seis años de

almacenamiento bajo condiciones ambientales y condiciones de temperatura

y humedad controladas en Tailandia

MICHAEL D. HARE1,2, NADDAKORN SUTIN2, SUPAPHAN PHENGPHET2 AND THEERACHAI SONGSIRI2

1 Faculty of Agriculture, Ubon Ratchathani University, Ubon Ratchathani, Thailand. www.ubuenglish.ubu.ac.th

2 Ubon Forage Seeds Co. Ltd., Jaeramair, Muang, Ubon Ratchathani, Thailand. www.ubonforageseeds.com/en/

Abstract

The germination performances of fresh seed lots were determined for 5 tropical forage species: Mulato II hybrid brachiaria [ Urochloa ruziziensis (syn. Brachiaria ruziziensis) x U. decumbens (syn. B. decumbens) x U. brizantha (syn.

B. brizantha)], Mombasa guinea [ Megathyrsus maximus (syn. Panicum maximum)], Tanzania guinea [ M. maximus (syn.

P. maximum)], Ubon paspalum ( Paspalum atratum) and Ubon stylo ( Stylosanthes guianensis), stored under ambient conditions in Thailand (mean monthly temperatures 23‒34 ºC; mean monthly relative humidity 40‒92%) or in a cool

room (18‒20 ºC and 50% relative humidity) for up to 6 years. The first paper of this study showed all seeds, except

unscarified Ubon stylo seed, were dead after a single year of storage in ambient conditions. This second paper shows

that cool-room storage extended seed viability, but performance varied considerably between species. Germination percentage under laboratory conditions declined to below 50%, after 3 years storage for Mombasa guinea seed and Tanzania guinea seed, 4 years for Ubon paspalum seed and 4‒5 years for Mulato II seed. Ubon stylo seed maintained

high germination for 5 years, in both cool-room storage (96%) and ambient-room storage (84%). Apparent embryo dormancy in acid-scarified Mulato II seed steadily increased with time in cool-storage and this seed had to be acid-scarified again each year at the time of germination testing to overcome dormancy. Physical dormancy of Mulato II

seeds, imposed by the tightly bound lemma and palea in unscarified seed, was not overcome by length of time in cool-

storage and these seeds had to be acid-scarified to induce germination. Hardseeded percentage in Ubon stylo seed remained high throughout the study and could be overcome only by acid-scarification. The difficulties of maintaining

acceptable seed germination percentages when storing forage seeds in the humid tropics are discussed.

Keywords : Embryo dormancy, hardseededness, humid tropics, seed storage, seed viability.

Resumen

En Tailandia se determinó la germinación de semilla de 5 cultivares de forrajeras tropicales: Urochloa híbrido cv. Mulato II, Megathyrsus maximus cv. Mombasa, M. maximus cv. Tanzania, Paspalum atratum cv. Ubon, y Stylosanthes guianensis cv. Ubon stylo, almacenadas bajo condiciones ambientales (temperaturas promedio mensuales 23‒34 ºC; humedad relativa 40‒92%) o controladas en cuarto frío (18‒20 ºC; 50% humedad relativa) durante 6 años. Mientras en

un estudio previo se encontró que bajo condiciones ambientales todas las semillas, excepto las de Ubon stylo no escarificadas con ácido, perdieron su viabilidad después de 1 año de almacenamiento, en este segundo estudio se encontró

que el almacenamiento en cuarto frío prolongó su viabilidad, aunque con una alta variabilidad entre especies. La germinación bajó a <50% después de 3 años de almacenamiento para M. maximus cvs. Tanzania y Mombasa, 4 años

___________

Correspondence: Michael D. Hare, Ubon Forage Seeds Co. Ltd., Muu

1 602 Tha Bor Road, Jaeramair, Muang, Ubon Ratchathani, Thailand.

Email: michaelhareubon@gmail.com

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Forage seed germination after 6-yr storage 27

para Paspalum atratum cv. Ubon y 4‒5 años para Urochloa híbrido cv. Mulato II. La semilla de S. guianensis cv. Ubon-stylo mantuvo una alta germinación durante 5 años de almacenamiento tanto en cuarto frío (96%) como bajo condiciones

ambientales (85%). La dormancia del embrión en las semillas de cv. Mulato II, escarificadas con ácido, aumentó constantemente con el tiempo de almacenamiento en cuarto frío; por tanto, para romperla fue necesario escarificar la

semilla con ácido nuevamente cada año en el momento de la prueba de germinación. De la misma forma, la dormancia

física de las semillas del cv. Mulato II impuesta por la lemma y pálea fuertemente unidas en semillas no escarificadas

con ácido, no se rompió con el tiempo de almacenamiento en cuarto frío, por lo que fue necesario escarificar con ácido

para inducir la germinación. El porcentaje de semilla dura de S. guianensis cv. Ubon-stylo permaneció muy alto durante todo el estudio y la germinación solo se pudo inducir mediante escarificación con ácido. Se discuten las dificultades para

mantener la germinación de las semillas y almacenar semilla de forrajeras en el trópico húmedo.

Palabras clave : Almacenamiento de semilla, dormancia del embrión, dormancia física, dureza de semilla, trópico húmedo, viabilidad.

Introduction

Mulato II and hardseededness in Ubon stylo persisted

under storage. However, embryo dormancy in Mombasa

Many tropical forage seeds produced and sold in Thailand

and Tanzania guinea grasses was overcome within 6

are stored under ambient conditions in store rooms and

months in cool-room storage (Hare et al. 2014).

shops where there is no control over temperature and

We used a commercial seed store (15 x 7 x 4 m) set at

humidity. The seeds are stored in conditions similar to those

18‒20 ºC and 50% RH. In this paper we report the

used to keep other grains for animal feed but which are not

performance of the initially tested seed lots under

required to germinate. Forage seeds are sometimes carried

prolonged cool-room storage at temperatures which were

over between years. There have been increasing concerns

higher than that used by Hopkinson and English (2005)

and reports about the declining germination quality of these

but with similar humidity.

forage seeds. In Australia, Hopkinson and English (2005)

stored tropical grass seeds in a cool-room (10 ºC and 50%

Materials and Methods

relative humidity, RH) and found that germination rates of

seeds initially with high viability remained high after 6 years

Seeds were harvested by village farmers from a number

cool-room storage. It was important for us to find the ideal

of villages in Northeast Thailand and Laos (Hare 2014) in

storage conditions in Thailand that would maintain seed

October 2010 (Ubon paspalum 5,000 kg, Mombasa

germination of our commercial forage seeds at acceptable

guinea 36,000 kg and Tanzania guinea 7,000 kg),

levels for more than 1 year.

November 2010 [Mulato II 12,000 kg: seed hand-knocked

We undertook an experiment on the germination of

from seed heads (Hare et al. 2007a)] and January 2011

commercial tropical forage seeds stored under ambient

[Mulato II 16,000 kg and Ubon stylo 6,000 kg: seed swept

conditions or under conditions of controlled temperature

from the ground (Hare et al. 2007a; 2007b)] and bulked

and humidity. Species represented were Mulato II

within species, harvesting method and season. All

[ Urochloa ruziziensis (syn. Brachiaria ruziziensis) x

harvested seeds were sun-dried to moisture levels in Table

U. decumbens (syn. B. decumbens) x U. brizantha (syn.

1, cleaned and processed and entered storage in late

B. brizantha)], Mombasa guinea [ Megathyrsus maximus

January 2011. For the experiment, Mulato II seeds (hand-

(syn. Panicum maximum)], Tanzania guinea [ M. maximus

knocked and ground-swept) and the Ubon stylo seeds

(syn. P. maximum)], Ubon paspalum ( Paspalum atratum)

were divided into two 3 kg sublots before storage; the first

and Ubon stylo ( Stylosanthes guianensis). All are com-

sublot was scarified in sulphuric acid (96% normal) for 10

mercial lines that are produced and sold in Thailand.

minutes, then washed and sun-dried to moisture levels in

The experiment commenced in January 2011.

Table 1, while the second sublot was left untreated

Germination results for the first 2 years (January 2011‒

(unscarified). All seed lots and sublots consisted of 3 kg

January 2013) were reported in a previous paper (Hare et

of seed drawn randomly from the total bulk of seed of

al. 2014). After 1 year of storage under ambient conditions,

each cultivar for the 2010/11 season, and placed into

seeds of all grasses tested were almost dead. After 2 years

separate large (100 x 50 cm) commercial polyethylene

cool-room storage (18‒20 ºC and 50% RH), germination

bags, hand-tied tightly at the top.

percentage of Mombasa guinea, Tanzania guinea and Ubon

The 3 kg bags of seeds consisting of one lot per bag

paspalum seeds had not declined. We also found that

were placed in 2 storage rooms, i.e. ambient conditions

apparent embryo dormancy and also physical dormancy in

and a cool-room (Hare et al. 2014). The ambient seed

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

28 M.D. Hare, N. Sutin, S. Phengphet and T. Songsiri

room was a storage shed at Ubon Ratchathani, Northeast

treatments with 3 replications. The entry means were

Thailand (15º N, 104º E), where mean monthly temper-

compared using Fisher’s protected LSD (P≤0.05).

atures were minimum 23 ºC, maximum 34 ºC and mean

monthly RH was minimum 40%, maximum 92%. The

Results

cool-room was maintained at 18‒20 ºC and 50% RH

throughout the study.

Moisture content

Seed samples were withdrawn from all storage lots in

January of each year and tested for germination and

Moisture contents of seeds stored in the cool-room varied

moisture percentage. For each germination test, 3

between 10.9 and 8.6% for the grasses and 8.3 and 5.1%

replications of 100 seeds, randomly selected from each

for Ubon stylo (Table 1). Acid-scarified Mulato II seeds

cultivar lot and sublot, were placed into covered petri

contained less moisture (9.1%) overall than untreated

dishes on filter paper wet with a 0.2% potassium nitrate

Mulato II seeds (9.8%). Mombasa guinea, Tanzania guinea

solution and placed in a germination cabinet set to provide

and Ubon paspalum seeds averaged 9.9% seed moisture in

16 h dark at 25 ºC and 8 h light at 35 ºC. The numbers of

cool-storage, similar to untreated Mulato II seeds (9.8%).

germinated seeds (normal seedlings), fresh ungerminated

Moisture level of untreated Ubon stylo seeds stored under

seeds or hard seeds, dead seeds and empty seeds were

ambient conditions was similar (5.5%) to that of untreated

Ubon stylo seeds in cool-storage (5.2%).

counted 7 and 14 days after wetting down. The

ungerminated seeds were tested using the tetrazolium

Seed germination

(TZ) assay test to determine if they were fresh

ungerminated (dormant), hard or dead.

Seeds of all grass cultivars maintained their germination for

For germination testing of acid-scarified Mulato II

2‒3 years in cool-storage before germination started to

seeds, further acid-scarification [sulphuric acid (96%

decline steadily and dead and empty seeds increased (Table

normal) for 10 minutes] was conducted at testing on half

2). After 6 years in cool storage, most seeds were either

the samples. To determine moisture percentage on each

dead [Mulato II hand-knocked (Table 2), Mombasa and

occasion, 3 samples of 10 g of seeds for each lot and

Tanzania guinea grasses (Table 3)], or had very low

sublot were weighed fresh and again after drying in an

germination [Ubon paspalum 2% (Table 3)] or had less than

oven at 130 ºC for 1 h (ISTA 1993). No seed moisture

10% germination [Mulato II ground-swept 9% (Table 2)].

levels were measured in 2017.

Only ground-swept Mulato II, that had been acid-scarified

Data from the experiment were subjected to analysis

upon entering cool-storage and acid-scarified again when

of variance using the IRRISTAT program from the

the germination test was conducted, gave a slightly better

International Rice Research Institute (IRRI). Each seed

seed germination of 15% after 6 years in storage. The

lot was analyzed separately with 7 years in storage as the

germination performance of Mulato II seeds, harvested by

Table 1. Effects of storage conditions on moisture contents of seeds of tropical forage cultivars during 2011‒2016.

Cultivar

2011

2012

2013

2014

2015

2016

Cool-room1

Mulato II ground-swept, acid-scarified3

7.5

8.5

9.9

8.0

10.1

9.6

Mulato II ground-swept, unscarified4

10.6

8.8

10.2

8.6

9.4

9.8

Mulato II hand-knocked, acid-scarified

8.9

8.6

10.0

8.3

10.2

9.8

Mulato II hand-knocked, unscarified

10.5

9.3

10.7

9.0

10.8

10.2

Mombasa guinea

10.3

9.2

10.4

9.2

10.7

9.9

Tanzania guinea

10.1

9.0

10.4

8.9

10.4

9.7

Ubon paspalum

10.4

8.9

10.3

9.5

10.9

10.4

Ubon stylo acid-scarified

8.3

7.2

8.0

6.7

8.5

7.8

Ubon stylo unscarified

5.1

5.2

5.2

5.4

5.4

5.1

Ambient-room2

Ubon stylo acid-scarified

9.3

9.25

Ubon stylo unscarified

5.1

5.2

5.8

5.7

5.4

5.5

118‒20 C and 50% RH. 2Range in mean monthly temperatures - minimum 23 ºC, maximum 34 ºC; range in mean monthly RH -

minimum 40%, maximum 92%. 3Scarified in sulphuric acid for 10 min, washed and dried. 4Not treated with acid. 5Seeds dead.

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)

Forage seed germination after 6-yr storage 29

Table 2. Effects of cool-room storage conditions (18‒20 ºC and 50% RH) on germination of differently treated seeds of Mulato II hybrid brachiaria during 2011‒2017.

Seed treatment

2011

2012

2013

2014

2015

2016

2017

LSD (P≤0.05)

14-day germination (%)

Mulato II ground-swept, acid-scarified1

85

62

63

53

33

3

1

8.1

Mulato II ground-swept, acid-scarified,

90

90

89

84

75

42

15

8.4

more acid with test2

Mulato II ground-swept, unscarified3

5

7

7

9

9

8

7

ns

Mulato II ground-swept, unscarified,

84

75

81

79

65

40

9

8.1

acid with test

Mulato II hand-knocked, acid-scarified

70

63

68

20

19

1

0

17.9

Mulato II hand-knocked, acid-scarified,

86

82

84

62

46

8

0

13.0

more acid with test

Mulato II hand-knocked, unscarified

0

1

1

3

4

1

1

ns

Mulato II hand-knocked, unscarified,

51

75

86

61

41

3

0

10.3

acid with test

Fresh ungerminated seeds (%)

Mulato II ground-swept, acid-scarified1

11

29

27

31

42

39

14

3.6

Mulato II ground swept, acid-scarified,

8

9

8

1

5

4

1

2.2

more acid with test2

Mulato II ground-swept, unscarified3

90

89

86

81

71

12

8

11.7

Mulato II ground-swept, unscarified,

12

19

14

14

15

10

9

ns

acid with test

Mulato II hand-knocked, acid-scarified

28

25

18

12

10

5

0

3.2

Mulato II hand-knocked, acid-scarified,

10

11

10

8

4

4

0

4.5

more acid with test

Mulato II hand-knocked, unscarified

97

91

89

40

8

0

0

3.3

Mulato II hand-knocked, unscarified,

46

20

10

9

7

6

0

6.5

acid with test

Dead and empty seeds (%)

Mulato II ground-swept, acid-scarified1

4

9

10

16

25

58

85

7.3

Mulato II ground swept, acid-scarified,

2

1

3

15

20

52

84

9.1

more acid with test2

Mulato II ground-swept, unscarified3

5

4

7

10

20

48

85

5.6

Mulato II ground-swept, unscarified,

4

6

5

7

20

50

82

10.3

acid with test

Mulato II hand-knocked, acid-scarified

2

12

14

68

71

94

100

18.9

Mulato II hand-knocked, acid-scarified,

4

7

6

30

50

88

100

10.9

more acid with test

Mulato II hand-knocked, unscarified

3

8

10

57

88

97

99

5.3

Mulato II hand-knocked, unscarified,

3

5

4

30

52

91

100

10.3

acid with test

1Scarified in sulphuric acid for 10 min, washed and dried. 2Scarified with sulphuric acid before storage and again before germination testing. 3Not treated with acid.

hand-knocking, deteriorated more quickly with time in

after 2 years in cool-storage (Table 3). By the third year in

storage than that of ground-swept Mulato II seeds (Table

cool-storage (2014), the germination of these 3 cultivars had

2). After 4 years in storage, mean germination percentages

declined rapidly to low levels (Table 3) and by the sixth year

of all lots of hand-knocked Mulato II seeds were below

(2017), seeds were either dead (Mombasa and Tanzania) or

50%, but it took 5 years in cool-storage for similar results

had negligible germination (Ubon paspalum). The percent-

to be reached with ground-swept Mulato II seeds.

age of fresh ungerminated seeds for all cultivars quickly