Tropical Grasslands-Forrajes Tropicales (2017) Vol. 5(2):94– 99 94
Short Communication
A simple method for determining maize silage density on farms
Un método sencillo para determinar la densidad en ensilaje de maíz a nivel
de finca
ANA MARIA KRÜGER, CLÓVES C. JOBIM, IGOR Q. DE CARVALHO AND JULIENNE G. MORO
Departamento de Zootecnia, Universidade Estadual de Maringá, Maringá, PR, Brazil. www.dzo.uem.br
Abstract
Several methodologies have been tested to evaluate silage density, with direct methods most popular, whereas indirect methods that can be used under field conditions are still in development and improvement stages. This study aimed to establish relationships between estimates of maize silage density determined using a direct and an indirect method, in an endeavor to provide an alternative to direct measurement for use in the field. Measurements were performed on maize silage in 14 silos. The direct method involved the use of a metal cylinder with a saw-tooth cutting edge attached to a chainsaw to extract a core of silage. Density of the silage was determined taking into consideration the cylinder volume and dry matter weight of silage removed at 5 points on the silage face. With the indirect method, a digital penetrometer was used to estimate silage density by measuring the penetration resistance at 2 points adjacent to the spots where the silage cores were taken, i.e. 10 readings per silo. Values of penetration resistance (measured in MPa) were correlated with the values of silage mass (kg/m3) obtained by direct measurement through polynomial regression analysis. A positive quadratic relationship was observed between penetration resistance and silage density for both natural matter and dry matter (R² = 0.57 and R² = 0.80, respectively), showing that the penetrometer was a reasonably reliable and simple indirect method to determine the density of dry matter in maize silage. Further testing of the machine on other silos is needed to verify these results.
Keywords: Ensiled matter, penetrometer, resistance, silos evaluation.
Resumen
Para determinar la densidad de ensilado, los métodos más usados son los directos mientras métodos indirectos, que se puedan usar a nivel de finca, están aún siendo desarrollados y mejorados. El objetivo de este estudio fue determinar la correlación entre las densidades de ensilado de maíz determinadas con un método directo, y las determinadas con un método indirecto. Las mediciones se hicieron en 14 silos de maíz de fincas lecheras en 5 municipios del estado de Paraná, Brasil. El método directo consistió en el uso de un cilindro metálico con un filo cortante de dientes serrados unido a una motosierra para extraer una muestra del ensilado; la densidad se determinó con base en el volumen del cilindro y el promedio del peso de las muestras extraídas en 5 puntos. El método indirecto consistió en el uso de un penetrómetro digital para medir la resistencia a la penetración en 2 puntos adyacentes a los sitios donde se tomaron las muestras del método directo (10 lecturas por silo). Los datos se sometieron a un análisis de regresión polinomial que mostró una relación cuadrática positiva entre la resistencia a la penetración (medida en MPa) y la densidad del ensilaje con base en los valores de la masa del ensilado (kg/m3) tanto para la materia natural como la materia seca (R² = 0.57 y R² = 0.80, respectivamente). Se concluye que el penetrómetro fue un método indirecto razonablemente confiable y sencillo para determinar la densidad de la materia seca en ensilado de maíz. Para verificar estos resultados se requieren pruebas adicionales con este equipo en otros silos.
.
Palabras clave: Evaluación de silos, materia ensilada, penetrómetro, resistencia.
___________
Correspondence: A.M. Krüger, Departamento de Zootecnia, Univer-
sidade Estadual de Maringá, Maringá CEP 87020-900, PR, Brazil.
E-mail: anamkruger@yahoo.com.br
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Determining silage density on farms 95
Introduction
Materials and Methods
Greater compaction of ensiled material provides greater
Specific mass measurements were made by a direct
specific mass (SM) by expelling air and providing
method in 14 bunker silos (treatments), employing
anaerobic conditions for fermentation. This allows better
methodologies described by Holmes and Muck (1999)
conservation of soluble sugars, minor alteration of
and D’amours and Savoie (2005), in maize silages on
structural carbohydrates and reduced proteolysis in the
dairy farms in Paraná State, Brazil, specifically in the
resulting silage, aspects which increase acceptability and
Castro, Carambeí, Arapoti, Piraí do Sul and Ponta Grossa
consumption by livestock (Velho et al. 2007).
municipalities.
Direct methods are used to evaluate SM of silages,
A metal cylinder, 20 cm length and 10 cm diameter,
with a serrated cutting edge and attached to a chainsaw,
mostly the determination of herbage mass for a known
was used, as described by Craig and Roth (2005) (Figure
volume of silage, with values being expressed in kg of
1). The cylinder was screwed into the silage panel
natural or dry matter per cubic meter. However, these
mechanically through the rotation exerted by the
methods involve measuring the volume of the sample,
chainsaw. When the sample was withdrawn from the
taking it to a suitable facility and drying it for at least 24
storage panel of the silo, the depth was measured with a
hours in an oven. More rapid, indirect methods, which
rule to calculate the volume of the withdrawn sample.
however require sophisticated equipment, aim to facilitate
From the cylinder volume and the mass [both natural
the collection of such data under field conditions, such as:
matter (NM) and dry matter (DM)] of the withdrawn
radiometric sensors that present a source and a receptor
sample, the SM of the silage in the silo was calculated.
for gamma waves, a method based on microwave
Whereas NM was the mass of the fresh silage, DM was
resonance; and the georadar system, also used to estimate
determined conventionally (weighing after drying NM at
SM of soils (Jobim et al. 2007).
105 °C for 8 h in a forced-air oven).
However, these indirect methods are still in
Silage samples were withdrawn at 5 points (taken as
development and improvement stages and rely on strict
replications) in the silo panel, 3 locations at the top and 2
calibration to produce reliable data. Among the various
at the bottom, forming a ‘W’ like figure. Before the
invasive tools to determine SM of silages, the
sampling procedure commenced, a slice of silage had
penetrometer has specific advantages over other
been removed manually from each silo panel in order to
techniques because it requires a simple calibration
remove any loose silage from the silage ‘face’, so that the
procedure and can provide reliable data. Sun et al. (2010)
samples were collected from ‘intact’ (undisturbed) silage.
suggested that this technique, when properly applied, has
To estimate SM through the indirect method, a digital
the potential to provide good information about silage
penetrometer (DLG, model PNT-2000-M), which follows
storage conditions. In an on-station study under controlled
the ASAE S313.3 rule that defines penetration resistance
conditions, Silva et al. (2011) correlated resistance values
as the pressure over the area of a cone with a solid angle
provided by maize silage to penetration by a penetrometer
of 30°, was used. This equipment is used to determine the
penetration resistance in soil compaction studies
with SM values obtained by sampling with the use of a
(Figueiredo et al. 2011; Storck et al. 2016). Penetration
metal cylinder of known volume. Estimates of SM they
resistance was measured at the same time and using the
obtained with this indirect method compared favorably
same orientation as in the direct determination with the
with values obtained with direct measurement, causing
metal cylinder, with 2 measurements of resistance at each
them to conclude that the penetrometer could provide
silo panel point, thus giving 10 measurements in each silo.
reliable estimates under field conditions both quickly and
Penetration resistance was measured at points adjacent to
at low cost.
the spots where silage samples were taken for the direct
The objective of our study was to measure the SM of
measurements, at a distance of approximately 35 cm from
maize silage on farms by a direct method (core sampling
those.
in the silo panel) and an indirect measurement method
For resistance measurements, the penetrometer metal
(using a penetrometer), and to establish correlations
cone was manually pushed into the silage panel
between the estimates obtained, with the aim of
horizontally at a constant speed of approximately 2 cm/s
establishing the penetrometer as a reliable tool for
up to the end of the cone length, a mandatory procedure
estimating the degree of compaction of stored forage in
according to the instruction manual for the device (Figure
the field.
2). Penetration depth into the silo panel was 0.9 m.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
96 A.M. Krüger, C.C. Jobim, I.Q. de Carvalho and J.G. Moro
direct method (in Table 1: observed SMNM and observed
SMDM). Data were not statistically analyzed, considering
that there was no replication (silo), since the silos were
evaluated on different farms and factors other than the
type of assessed silo and silage (maize) may present
different characteristics. Therefore, the values obtained
for the SMNM and SMDM were descriptively analyzed.
Figure 1. Cylinder and chainsaw in use. Source: Personal file.
Penetrometer resistance values (in megapascal, MPa)
were correlated with the SM values (kg/m³) obtained with
use of the cylinder coupled to the chainsaw by a
polynomial regression study. The regression equations
obtained were used to calculate the values of SM for
natural matter (SMNM) and dry matter (SMDM) in each
silo (in Table 1: estimated SMNM and estimated SMDM)
and these were compared with the values obtained by the
Figure 2. Penetrometer in use. Source: Personal file.
Table 1. Dry matter concentration, resistance by ensiled mass to penetration of the metal cone (± SD), observed and estimated specific mass (natural matter and dry matter basis) (± SD) in 14 farm silos.
Silo
DM1
Resistance
SMNM (kg NM/m3)
SMDM (kg DM/m3)
(g/kg)
(MPa)
Observed
Estimated
Observed
Estimated
1
327
2.20 + 0.50
839 + 80.5
767 + 45.3
274 + 26.3
260 + 11.6
2
350
1.92 + 0.35
748 + 48.8
837 + 14.9
262 + 17.1
282 + 4.8
3
292
0.24 + 0.05
469 + 90.8
571 + 17.2
137 + 26.5
146 + 7.5
4
277
0.54 + 0.10
751 + 108.7
704 + 25.7
208 + 30.1
204 + 11.6
5
294
1.07 + 0.40
876 + 49.5
850 + 47.9
258 + 14.6
271 + 24.3
6
274
1.00 + 0.14
904 + 73.0
837 + 22.1
247 + 20.0
265 + 10.7
7
336
0.99 + 0.35
787 + 62.7
836 + 49.1
265 + 21.1
264 + 24.0
8
287
0.68 + 0.22
787 + 87.4
755 + 48.4
226 + 25.1
227 + 22.1
9
279
0.74 + 0.25
801 + 22.9
773 + 50.8
223 + 6.4
235 + 23.5
10
325
1.15 + 0.29
854 + 126.2
861 + 39.2
277 + 41.0
277 + 19.3
11
391
1.06 + 0.14
710 + 103.2
847 + 23.1
277 + 40.3
270 + 11.1
12
345
0.85 + 0.37
867 + 67.4
803 + 73.7
299 + 23.2
248 + 34.1
13
278
0.48 + 0.24
776 + 59.8
684 + 62.6
216 + 16.6
195 + 28.0
14
270
0.53 + 0.18
660 + 50.6
702 + 47.2
178 + 13.6
203 + 21.2
Mean
309
0.96 + 0.58
773 + 128.5
773 + 71.0
239 + 48.4
239 + 34.3
1DM – dry matter; NM ‒natural matter; Resistance – resistance to penetration of the metal cone; SMNM – specific mass of natural matter; SMDM – specific mass of dry matter.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Determining silage density on farms 97
Results
Discussion
The average DM concentration found in the silages
The values observed for DM concentration of the silages
evaluated was 309 g DM/kg, ranging from 270 to 391 g
evaluated are consistent with the recommendation of
DM/kg (Table 1). Density of silage as determined by the
Nussio et al. (2001) that the optimal DM concentration of
direct method (‘observed’) ranged from 469 to 904 kg/m3
maize plants at ensiling should be 300‒350 g DM/kg.
(mean 773 ± 129 kg/m3) for NM and from 137 to 299
According to these authors, DM concentrations below
kg/m3 (mean 239 ± 48.4 kg/m3) for DM. The density
300 g DM/kg are associated with lower DM yield, losses
measurements were compared with the range in
by leaching and low silage quality, factors that may lead
penetration resistance in the silos, which varied from 0.24
to reduced intake by animals. The quality of silages was
to 2.20 MPa (mean 0.96 ± 0.58 MPa). The results for this
evidenced by parameters such as neutral detergent fiber,
comparison are shown in Figures 3 and 4.
starch content and pH, which presented mean values of
46.35 ± 4.8 %, 33.28 ± 4.62 % and 3.81 ± 0.07, respective-
ly (A.M. Krüger unpublished data).
The values obtained using the direct method indicated
that there was considerable variation in how well the
material was compacted in the silos, which can be related
to the method of compaction used, the stage of growth of
the forage when ensiled, the moisture content of the
forage at ensiling, etc. According to Jobim et al. (2007),
although there is no optimal value for silage density,
values in the range of 550‒850 kg NM/m³ are most
suitable, and these are obtained only under favorable
conditions. Typically, appropriate compression for
desirable fermentative characteristics and minimal losses
in maize silage is obtained with minimum SMDM around
225 kg DM/m³. The majority of the silages sampled were
above this minimum level. One might expect that the
nutritional value and acceptability of the silage to
Figure 3. Relationship between SMNM (specific mass based
on natural matter), expressed in kg/m³ and resistance to
livestock would also vary markedly.
penetrometer metallic cone, expressed in MPa.
The penetration resistance observed when employing
the indirect method indicates that, while there was marked
variation in density of the silage as measured directly,
there was much greater variation in resistance as
measured by the penetrometer. If one assumes that the
density measurements were accurate, one might question
the accuracy of the penetrometer readings for the same
silages.
In an experiment in which 18 penetrometer measures
were performed in one silage sample kept under
controlled conditions in an experimental station, Silva
et al. (2011) found a mean penetrometer resistance of
1.09 ± 0.23 MPa and specific mass observed based on dry
matter of 170 ± 36.5 kg DM/m³. As in the present study,
resistance values obtained were compared with direct
measurements as well.
The results obtained for SM (Table 1) observed (direct
method) and estimated (indirect method), both for NM
Figure 4. Relationship between SMDM (specific mass based
and DM, are consistent with those typically observed in
on dry matter), expressed in kg/m³ and resistance to
farm silos and the values found by the indirect method
penetrometer metallic cone, expressed in MPa.
presented a smaller range of variation when compared
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
98 A.M. Krüger, C.C. Jobim, I.Q. de Carvalho and J.G. Moro
with the direct method, because regression equations
silages with SMDM above 260 kg DM/m3 had DM % in
determine the middle pathway and reduce the effect of
the range 325‒391 g DM/kg. All silages with penetro-
outlying values. There was a positive relationship
meter readings below 0.75 MPa had DM % below 300 g
between the SM of silage and penetration resistance to the
DM/kg and SMDM below 230 kg DM/m3. The relation-
metal cone (Figures 3 and 4). This was a curvilinear
ship between DM concentration in silage and reliability
relationship with silage SM increasing as the resistance to
of the machine needs to be investigated further to confirm
the cone penetration increased to a peak of about 900 kg
these findings.
NM/m3 or 300 kg DM/m3.
Silva et al. (2011) observed a positive linear
Acknowledgments
relationship between the SM of maize silage and
penetration resistance to the metal cone in 2 experiments.
The authors thank CNPq (National Council for Research
However, in 1 of the experiments, the adjusted linear
and Technological Development) for the financial
equation had a low coefficient of determination,
support.
explaining only 33% of the observed variation. This low
coefficient was attributed to surface conformations of
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(Received for publication 31 August 2016; accepted 22 February 2017; published 31 May 2017)
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