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)
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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
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
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
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
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.
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
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
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
( Heteropogon
Queensland
humilis
contortus)
Native
Australia,
Dry tropics
Centrosema
-183 g/an/d
489 g/an/d
Northern Territory
pascuorum 1
Urochloa
Australia,
Dry tropics
Leucaena
381 g/an/d2
723 g/an/d2
mosambicensis Northern
leucocephala cv.
Queensland
Cunningham
L. diversifolia
532 g/an/d2
Brachiaria
Venezuela,
Humid tropics
Desmodium
336 g/an/d
385 g/an/d
humidicola 3
Táchira
ovalifolium 4
Brachiaria
Colombia, Llanos
Subhumid
Pueraria
124 kg/an/yr
174 kg/an/yr
decumbens 5
(savanna)
phaseoloides
Andropogon
Colombia, Llanos
Subhumid
Stylosanthes
120 kg/an/yr
180 kg/an/yr
gayanus
(savanna)
capitata
240 kg/ha/yr
280 kg/ha/yr
Brachiaria
Colombia, Llanos
Subhumid
Centrosema
191 g/an/d6
456 g/an/d6
dictyoneura3
(savanna)
acutifolium cv.
Vichada
Stylosanthes
446 g/an/d6
capitata
Brachiaria
Brazil, Mato
Subhumid
Calopogonium
327 kg/ha/yr
385 kg/ha/yr
decumbens 5
Grosso do Sul
(savanna)
mucunoides
Pennisetum
Brazil, Santa
Humid
Arachis pintoi
716 g/an/d
790 g/an/d
purpureum cv.
Catarina
subtropical
Kurumi
Brachiaria
Costa Rica,
Humid tropics
Arachis pintoi
139 kg/an/yr8
166 kg/an/yr8
brizantha 7
Guápiles
597 kg/ha/yr8
736 kg/ha/yr8
Brachiaria
Mexico, Veracruz
Wet-dry tropics
Cratylia argentea
580 g/an/d
839 g/an/d
brizantha 7
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
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
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
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
(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
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-
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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© 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
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
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
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–
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445. DOI: 10.1590/S1516-35981999000300001
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Andrade CMS de; Valentim JF; Carneiro JC. 2002. Árvores de
matter in intermediate stages of decomposition (Souza et
baginha ( Stryphnodendron guianense (Aubl.) Benth.) em
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ecossistemas de pastagens cultivadas na Amazônia
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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)
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
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
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.
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cycle assessments are necessary to determine what
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
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
