Citation of this paper

The effect of molasses on the chemical composition of ensiled soybean forage (Glycine max L. Merr.)

Nguyen Thi Thu Hong^1,2, Nguyen Thi Ngoc Trang³, Danh Mo³ and Duong Hong Duyen⁴

¹ An Giang University, An Giang, Vietnam
ntthong@agu.edu.vn
² Vietnam National University Ho Chi Minh City, Vietnam
³ Kiengiang University, Vietnam
⁴ Agriculture Extension Center of An Giang province, Vietnam

Abstract

The experiment was carried out in An Giang province to evaluate the effect of adding molasses to silage made from soybean forage [Glycine max (L.) Merr.] harvested following collection of the green pods at 70 days. The treatments were 0, 2, 4 and 6% of molasses (DM basis) replicated 4 times in micro-silos (plastic bags) with separate silages made for opening (and taking samples for analysis) after 7, 14, 21, 28, 60 and 90 days.

The addition of 2% molasses (DM basis) in the ensiling of soybean foliage resulted in better quality silage as measured by the reduction in pH and levels of ammonia after 90 days of preservation.

Key words: ammonia, fermentation, silage quality

Introduction

Soybean forage (Glycine max L. Merr.) (Edamame) varieties developed for grain production could potentially be harvested as forage in tropical environments for feeding to livestock (Mustafa et al 2003). Soybean forage is difficult to preserve as silage due to the relatively low concentration of soluble carbohydrates and relatively high buffering capacity because of the high content of protein. However, this limitation is easily overcome if an additional source of soluble carbohydrates is added to the silage. Addition of sugar cane molasses not only facilitates soybean silage fermentation but also improves silage sensory characteristics (Tobía et al 2007). Soybean silage appears to be a good alternative to take advantage of the nutritional value of this legume in the wet tropics (Tobía et al 2008).

The objective of this research was to quantify indicators associated with the process of ensiling soybean forage with sugar cane molasses.

Material and methods

Location

This experiment was carried out oon a farm in Chauphu district, An Giang province

Design and treatments

The experiment was designed as a completely randomized block with four treatments and 4 replications. The treatments were: 0, 2 ,4 and 6% molasses added to the soybean forage (DM basis) which was harvested after 70 days of growth following collection of the green pods. All treatments were supplemented with 1% salt (DM basis).

Procedure

The soybean foliage was chopped in approximately 2 cm sections and sun-dried for 2-3 h to reduce the moisture to about 70%. Molasses was applied prior to storage in plastic bags as micro-silos (Photos 1 and 2). Each treatment/replicate was ensiled in 6 separate plastic bags to be able to take samples for analysis after periods of 7, 14, 21, 28, 60 and 90 days.


Photo 1. The soybean was mixed with molasses and salt	Photo 2. The mixtures were packed into plastic bags of 1 kg capacity

Measurements and chemical analysis

The pH (digital meter) and ammonia-N were determined on fresh samples of silage. Other samples were dried at 55°C for 48h then ground through a 1mm screen prior to proximate analysis according to AOAC (1990). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were analysed using the method of Van Soest and Robertson (1985). The solubility of the protein was determined by shaking 3 g of dried samples in 100 ml of 1M NaCl for 3h then filtering through Whatman No. 4 filter paper, and determining the N content of the filtrate (Whitelaw and Preston 1963).

Statistical analysis

The data were analyzed by the general linear model in the Minitab software (Minitab 2010). Sources of variation were: treatments, repetitions and error.

Results and discussion

The relatively high values for the solubility of the protein (Table 1) indicate that it would be mainly fermented in the rumen and have little “escape” or “bypass” protein (Preston and Leng 1987).

Table 1. Chemical composition of the soybean foliage and molasses
	Soybean foliage	Molasses

Dry matter, %	23.9	58.3
As % of DM
Crude protein	15.9	8.6
Ash	8.10
ADF	33.1
NDF	48.4

	Soybean foliage
	Leaf	Stem
Protein solubility %	47.8	69.8

The pH of 5.31 after 90 days of ensiling (table 2) indicates the need for additional soluble carbohydrate and that as little as 2% molasses (DM basis) was sufficient to maintain the pH below 4 (Table 2). The reduction in ammonia from 4.1 to 2.7mg/g DM is further proof of the need for the addition of rapidly fermentable carbohydrate when ensiling soybean foliage.

Table 2. Effect of molasses levels on ensiling characteristics of Soybean forage
	Days of ensiling
	7	14	21	28	60	90

pH
SFM0	6.69^a	6.57^a	6.54^a	6.22^a	5.41^a	5.31^a
SFM2	5.54^b	5.22^b	4.75^b	4.40^b	4.13^b	3.95^b
SFM4	5.37^bc	4.18^c	3.97^c	3.87^b	3.86^b	3.83^b
SFM6	5.08^c	4.31^c	3.95^c	3.74^b	3.96^b	3.87^b
SEM	0.10	0.11	0.11	0.17	0.10	5.30
p	0.001	0.001	0.001	0.001	0.001	0.001
Ammonia, mg/g DM
SFM0	1.12^a	1.41^a	1.139^a	1.096^a	0.0313^a	4.114^a
SFM2	0.739^b	0.876^b	0.731^b	0.740^b	0.0231^b	2.678^b
SFM4	0.561^b	0.718^b	0.689^b	0.710^b	0.0174^c	2.431^bc
SFM6	0.514^b	0.723^b	0.612^b	0.574^b	0.0157^c	1.972^c
SEM	61.8	0.043	0.067	0.076	0.0114	0.123
p	0.001	0.001	0.002	0.005	0.001	0.001
Dry matter, %
SFM0	16.6	17.7	16.8	16.8	16.3	15.4
SFM2	17.7	18.0	16.8	16.7	16.4	16.5
SFM4	17.6	18.5	17.9	17.5	18.2	17.5
SFM6	17.9	17.2	18.9	18.6	18.0	17.9
SEM	0.55	0.37	0.36	0.27	0.52	0.78
P	0.370	0.181	0.008	0.002	0.058	0.168
^abcdMeans in the same column, within a given measurement criterion, without common superscript differ at r p<0.05

Conclusions

The addition of 2% molasses (DM basis) in the ensiling of soybean folaige resulted in better quality silage as measured by the reduction in pH and levels of ammonia after 90 days of preservation.
The relatively high values for the solubility of the protein) indicate that it would be mainly fermented in the rumen and have little “escape” or “bypass” properties.

References

AOAC 1990 Official Methods of Analysis, 15^th editon. Association of the Official Analytical Chemists, Washington D.C.

Minitab 2010 Minitab reference manual release 16.20. Minitab Inc.

Mustafa A F and Seguin P 2003 Characteristics and in situ degradability of whole crop faba bean, pea, and soybean silages. Can. J. Anim. Sci. 83:793-799.

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