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Nutrient Content of Silages Made from Whole-Plant Soybeans1
The Professional Animal Scientist 11 :74-80
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from Whole-Plant Soybeans1 K. P. COFFEy2, PAS, G. V. GRANADE3, and J. L. MOYER Kansas State University - Southeast Agricultural Research Center, Parsons, KS 67357 University of Georgia,Georgia Experiment Station, Griffin, GA 30223
Abstract Whole-plant soybean forages were chopped and ensiled in 1988 and 1989 from plots in a 2 x 3 x 2 factorial arrangement of a randomized complete block design. Maturity group IV (,Stafford') vs group V ('Bay') soybean forages were harvested and ensiled at either full bloom (R2), full pod (R4), or full seed (R6) growth stages, with (1) or without (NI) a silage inoculant for a minimum of60 d in lined 19-L containers. Dry matter yield of Bay in both years and Stafford in 1989 increased (P<.OS) with advancing growth stage, and R2 and R6 Bay yields were greater (p<.OS) than R2 and R6 Stafford yields. Three-way interactions were detected (p<.OS) for silage pH; total volatile fatty acids (VFA); and molar proportions of acetic, isobutyric, and butyric acids in 1988 and of acetic and butyric acids in 1989. Silages harvested at R6 had the highest (p<.OS) lactic acid and lowest (p<.OS) ammonia concentrations in
1988 and the lowest (p<.OS) total VFA in 1989. Bay had greater ethanol and ADL and lower N concentrations in both years (p<.OS) and lower pH, ammonia, and total VFA and higher NDF and ADF in 1989 than Stafford (p<.OS). Inoculated silages had lower (P<.Ol) molar proportions of propionate in 1988 and higher (p<.01) total VFA in 1989 than NI. Silages harvested at R2 had higher N in 1988 and lower ADL in both years than those harvested at R4 and R6 (p<.OS). Neutral-detergent fiber content at R4 was higher (p<.OS) than at R2 and R6 in 1988 and higher (p<.OS) than at R2 in 1989. Considering the relative magnitude of changes in yield and quality with advancing maturity, one should delay harvesting soybeans for silage until the R6 growth stage, if possible. (Key Words: Soybean, Silage, Forage Quality, Growth Stage, Silage Inoculant.)
Introduction 1 Contribution no. 95-158-J from the Kansas Agric. Exp. Sta., Manhattan, KS, 66506.
2Kansas State University. 3University of Georgia. Reviewed by D. C. Anderson and L.
J.
Bush.
Soybeans [Glycine max (1.) Merr.] are grown in the United States primarily for seed production. Adverse weather conditions often interfere with the harvest of quality soybeans. Late spring rains, early frosts, dry summers, or combinations of these factors can occur, resulting
in reduced seed yields, small or otherwise lower quality seed, or green seed. The market price of these lower quality soybean seeds may be reduced substantially. Previous research to find alternative uses for soybeans to minimize the risk associated with adverse weather or marketing conditions have centered on its value as a hay crop (11, 17 ,19) . Although soybeans also have been intercropped with corn (4, 7) or sorghum (2, 8, 12) to improve the protein content of a subsequent silage crop, evaluation of monocultured soybeans as a silage crop has been limited. The objectives of this experiment were to determine 1) differences in quality and yield between ensiled whole-plant Stafford (maturity group IV) and Bay (maturity group V) soybeans; 2) yield and quality of silages produced by harvesting soybeans at different growth stages; and 3) the effect of a silage inoculant on quality of whole-plant soybean silages.
Materials and Methods Forty-eight four-row plots, 9.1 -m in length, having a .76-m row spacing were established in 1988 and 1989 on an area of Parsons silt loam soil. Plots were arranged in four blocks of 12 plots each in a random-
75
Silages of Whole-Plant Soybeans
ized complete block design (20). Half of the plots were seeded to a maturity group IV soybean cultivar ('Stafford'), whereas the remaining half were seeded to a maturity group V soybean cultivar ('Bay'). The center two rows from two plots of each cultivar within each block were harvested with a forage chopper at either R2, R4, or R6 growth stages (9j Table 1). The forage from one of each pair of plots within a block was inoculated (1) with .03 g/kg Biomate LP/PC® (Chr. Hansen's Lab., Inc., Milwaukee, WI) to provide 100,000 cfu of Lactobacillus plantarum and Pediococcus cerevisiae/g of forage. The forage from the remaining plot of each pair within a block was not inoculated (NI). All forages were packed into 19-L plastic containers lined with three plastic trash can liners and allowed to ferment for a minimum of 60 d. Three or four of the experimental silos were opened daily over a 13-d period at the time of feeding during a consumption study using lambs. Fresh samples (2S g) were blended with distilled water (100 ml) and allowed to stand at room temperature for 1 h and then pH was measured. One hundred milliliters of .4 N HzSO 4 was added to the solution, and the mixture was allowed to stand for 48 h. The solution then was strained through four layers of cheesecloth and stored frozen
(-20°C) prior to analysis for volatile fatty acids (VFA), lactate, ammonia, and ethanol. Another fresh silage sample was dried at SO°C and ground (1 mm) for quality analyses after allowing a minimum of 72 h for equilibration to atmospheric moisture. Sample dry matter was determined by drying overnight at lOS°C. Samples were digested in HzSO 4-HPZ (IS) and analyzed for N content by colorimetric techniques of Crooke and Simpson (6) and for P content by colorimetric techniques of Kitson and Mellon (14). Calcium concentrations were determined by atomic absorption spectrophotometry after samples were digested according to the procedures of Blancher et al. (3). Neutral-detergent fiber, ADF, and acid-detergent lignin (ADL) were determined using procedures of Goering and Van Soest (10) as modified by Jeraci et al. (13). Ammonia was determined by microdiffusion (S), and lactate according to a modified procedure of Barker and Sommerson (1). Ethanol and VFA were determined using a HewlettPackard S730A gas chromatograph having a 1.83-m Chromosorb 101packed column at 200°C, a flow rate of 60 ml/min, and a flame ionization detector temperature of 2S0°C. Yield and quality data were analyzed using SAS® (18) General Linear Models (GLM) procedures for
TABLE 1. Growth stages at which soybeans were harvested for silage (9). Growth
R2 R3 R4 RS R6 R7
stage
Definition
Flower present at node immediately below the uppermost node with a completely unrolled leaf. Pod is .S cm long at one of the four uppermost nodes with a completely unrolled leaf. Pod is 2 cm long at one of the four uppermost nodes with a completely unrolled leaf. Beans beginning to develop at one of the four uppermost nodes with a completely unrolled leaf. Pod containing full size green beans at one of the four uppermost nodes with a completely unrolled leaf. Pods yellowing; SO% of the leaves yellow; physiological maturity.
a split-plot design experiment. Year, replicate, and their interaction were included in the model as the wholeplot effects. Year and replicate effects were tested using their interaction as the error term. Subplot effects were cultivarj growth stagej inoculant; all two- and three-way interactions among cultivar, growth stage, and inoculant, and all interactions with year. Upon detection of interactions of cultivar, growth stage, or inoculant with year, the analysis was conducted within year using SAS® (18) GLM procedures for a 2 x 3 x 2 factorial arrangement of a randomized complete block design. The model consisted of effects of cultivar, growth stage, inoculant, and all interactions. Differences among treatments were tested using a protected t test (20).
Results and Discussion Interactions of year with either cultivar, growth stage, or inoculant were detected (P<.OS) for most constituents measured. Therefore, data for this study were analyzed and reported within year. Bay soybean forage had greater (P<.OS) DM content than Stafford forage at the R2 growth stage in both years, at R6 in 1988, and at R4 in 1989 (Table 2). Bay and Stafford soybean forages did not differ (P>.10) in their DM content at R4 in 1988 and at R6 in 1989. Dry matter percentage of both cultivars increased (P<.OS) with increasing growth stage in 1988 and was greater (P<.OS) for both cultivars at R6 than at R2 or R4 in 1989. Forage DM yields from Bay soybeans were greater (P<.OS) than yields from Stafford soybeans in both years at R2 and R6 growth stages. Forage DM yields from R2 Bay soybeans averaged 30% greater (P<.OS) than DM yield from R2 Stafford soybeans, and yields from R6 Bay soybeans averaged 21.9% greater (P<.OS) than DM yield from R6 Stafford soybeans. Forage DM yields from soybeans harvested at the R4 growth stage did not differ between cultivars in either year. Forage DM yields from Bay
76
Coffey et al.
TABLE 2. Dry matter percentage and yield of whole-plant soybeans harvested for silage. Stafford
R,.v
--J
Year and variable
R2
R4
R6
R2
R4
R6
SE
22Ad
29Ac
36.7a
21Ae
28.7 c
31.5 b
.31
16.6c 3.7 c
19.5 b 5.7 b
21.sa . 7.9 a
. 13Ad 2.9 d
19.7 ab 5.7 b
19.0 b 6.0 b
.66 .20
Divi, 0/0
.... '" 1 h £:1.1-
""' ....... h £.J."t-
26.3 2
""1 ... r £ I."t-
£ 1.£ -
.... 1
2s.sa
.:1V
Yield, mg/ha Fresh DM
17.8d 4.1d
22.8 c 5.3 c
29.5 a 7.7 a
14Ae
24.7 bc 5.2c
26.3 b 6.8 b
.75 .17
1988 DM,% Yield, mg/ha Fresh
DM 1989
3.1 e
.... ,.
..,,,
a-eMeans within a row with no common superscript differ (P<.05).
TABLE 3. Silage characteristics from ensiled whole-plant soybeans with (I) or without (NI) an inoculant. Stafford
Bay Year and characteristic 1988 pHf Lactic9, %
I NI I NI
Ammoniag, %
i
ETOHhi, %
NI I NI
1989 pH hi Lactichi, %
I NI I N!
Ammonia 9i, % ETOH9 i, %
I NI I NI
R2
R4
R6
5.6 bc 5.9a 1.5 .7 .5 7 .69 .04 .10
5.2e 5.7 ab .8 .8 .38 .57 .28 .34
4.7f 4.61 5.0 4.9 .i 9 .26 .24
5.1 5.1 .8 1.2 .13
5.2 5.3 .6 1.0
4.8 5.0 2.6 1.9
.11 .26 .09
041
.11
.11
.10 .24 .16
.10 .63 .77
a-eMeans within an item with no common superscript differ (P<.05). fCultivai x giOwth stage x inoculant (P<.05). gGrowth stages differed (P<.05). hGrowth stage x inoculant (P<.05). iCultivars differed (P<.01). iCultivar x growth stage (P<.01).
R6
R2
R4
5.7 abc
5.6 bc 5.8 ab .5 .5 .58 .58 .06 .23
4.9f 5.2 de 2.7 3.6 .25 .35 .18
5.8 5.5 .6 1.0 .16 .09 .06 .04
4.9 5.3 1.5 1.1
5Acd
.9 1.5 .62 .51 .01 .01 5.5 SA A .4
.17 .16 .08 .09
SE
.09 .60
.058 .046
041
.10 .22
.11
.016
.13 .38 .61
.113
77
Silages of Whole-Plant Soybeans
TABLE 4. Volatile fatty acid (VFA) concentrations from ensiled whole-plant soybeans with (I) or without (NI) an inoculant. Stafford
Bay
R2
Year and VFA
1988 Total VFAe, IJmol/g DM
I NI
870.3 cde 1218.7 ab
R4
R6
R2
889.2bcd 735.1 cde
638.5 de 532.2e
1023.6abc 1052.6abc
R4
R6
SE
959.3 bcd 1322.13
984.4 abcd 539.5 e
120.84
79 .2 cde 62.3 1 5.2 7.7 1.9 bc S.2a 13.0abc 20.7 a .0 1.9 .7 2.2
98.4 a 80.6 bcde .0 2.3 .Od .3 cd .Od 13.0abc .7 1.3 .9 2.5
4.25
(mo1 / 100 mol)
Acetie e Propionicl9 Isobutyriee Butyrice Isvaleric Valerie 1989 Total VFA9 hi, IJmol/g DM
I NI I NI I NI I NI I NI I NI I NI
89.6 abc 71.5 ef 3.1 4.7 .6 bcd 1.7bcd 4.8 cd 20.8 a .S .6 1.4 .6 1319.S 1124.7
91.4 abc 77.0 de .9 3.7 .Od 1.2bcd 5.7 bcd 14.7 ab 1.1 2.7 .9 .6 1085.6 861 .6
98.8 a 91.7 ab .2 .4 .Od .Od .Od 1.3d .5 4.9 .S 1.7 641.7 704.2
88.5 abcd 90.13bc 4.0 3.2 2.1 ab .6 bcd S.4 cd S.ocd .0 .8 .0 .4 1609.7 1S07.1
1493.9 1188.3
908.7 826.2
.83 .61 3.19 1.41 .91
80.15
(mol/l 00 mol) Acetic e Propionie i Isobutyric! Butyriee Isovaleric Valeric i
I NI I NI I NI I NI I NI I NI
96.2a 94.9 ab 3.3 3.3 .0 .1 .Oc 1.F .0 .0 .5 .S
94.8 ab 9S.4 a 2.2 3.1 .0 .0 2.Sbc .Oc .0 .0 .S loS
9S .3a 96.9 a 2.4
1.1 .0 .0 .Oc .Oc .0 .0 2.2 2.0
83.8 cd 8S.8 bcd 3.0 3.2 .6 1.4 11.9a 8.6 ab .0 .0 .8 1.0
76.6 d 91.6 abc 6.7 3.1 3.1 1.5 12.5 a 2.9 bc .1 .0 .9 .9
96.Sa 83.1 cd 2 .3 1.3 .0 .0 .Oc 14.13 .0 .0 1.2 loS
3.26 1.04 .S6
2.34 .02 .40
a-dMeans within an item with no common superscript differ (P<.OS). eCultivar x growth stage x inoculant (P<.OS). fCultivar x growth stage (P<.01). 91noculated silages differed (P<.01) from noninoculated silages. hCultivars diffe red (P<.01). iGrowth stages differed (P<.OS).
soybeans in both years and Stafford soybeans in 1989 increased (P< .OS) with advancing growth stage. Ensiled R6 Bay and Stafford soybeans averaged 2.03 an d 2.13 times the DM yield of R2 Bay and Stafford soybeans, respectively. Munoz et al. (17)
reported similar increases in wholeplant soybean yield with advancing growth stage through R7. Cultivar x growth stage x inoculant interaction s were detected (P<.OS) in 1988 for silage pH (Table 3). Silages having the lowest pH were
I and NI R6 Bay and I R6 Stafford soybeans. Noninoculated R2 and R4 Bay and R4 Stafford and I R2 Stafford silages tended to have the highest pH. Lactic add concentrations were greater (P<.OS) and ammonia concentrations lower (P<.OS) from R6 silages
78
Coffey et ai.
(P<.OS) in 1988 for total VFA and molar percentages of acetic, TABLE 5. Effects of cultivar and silage inoculant on quality of silages and butyric acids (Table isobutyric, made from whole plant soybeans (OM basis) . 4) . Total VFA were numerically \...UllIVcU lowest in 1988 from Ni R6 Bay and quality Stafford silages and numerically characteristic Stafford SE NI SE Bay highest from NI R4 Stafford silage. The greatest molar percentage of total 1988 VFA was present as acetic acid in Na 2.7 2.8 .04 2.7 2.7 .04 both years. In 1988, molar percentNDF 48.3 49.2 .59 48.5 48.9 .61 age of acetic acid was numerically ADF .51 38.1 37.3 37.5 37.9 .51 highest from the I R6 silages and ADLb 7.4 6.8 .14 7.0 7.2 .14 numerically lowest from NI R4 Cac 1.49 1.50 .014 1.46 1.54 .014 pbd Stafford silage. Noninoculated silages .27 .29 .004 .27 .29 .004 1989 had greater (P<.Ol) molar proporNb 3.0 3.3 .04 3.1 3.2 .04 tions of propionic acid than I silages NDFb 39.7 38.3 39.3 .33 38.8 .33 when averaged across cultivars and ADFb 28.3 27.3 .29 28.0 27.6 .29 growth stages. Ensiled R4 Stafford ADLb 6.7 6.0 .09 6.4 6.3 .09 soybeans had the highest (P<.OS) and Ca 1.36 1.43 .049 1.38 1.4 1 .049 R6 silages the lowest (P<.OS) molar pb .31 .26 .005 .29 .28 .005 proportion of propionic acid. Molar proportions of isobutyric and butyriC aSiiages made from Bay soybeans differed (P<.05) from silages made from acids tended to be lowest from I R6 Stafford soybeans. Bay and Stafford silages and from NI bSilages made from Bay soybeans differed (P<.01) from silages made from Bay R6 silage. Butyric acid tended to Stafford soybeans. be highest from NI R2 Bay and R4 clnoculated silages differed (P<.05) from noninoculated silages. Stafford silages. Isovaleric and valeric dlnoculated silages differed (P<.1 0) from noninoculated silages. acid molar percentages did not differ (P>.1O) among cultivars, growth stages, or inoculant treatments in est (P< .OS) concentrations of lactic than from R2 or R4 silages. Bay 1988. acid, NI R6 silages were intermediate, No interactions were detected for silage had greater (P< .Ol) ethanol total VFA in 1989. Ensiled Stafford concentrations than Stafford silage. and all R2 and R4 silages had the Inoculated R4 and R6 silages had soybeans had greater (P<.Ol) VFA lowest lactic acid concentrations. A reduced (P<.OS) ethanol concentraconcentrations than ensiled Bay cultivar x growth stage interaction tions compared with NI R4 and R6 also was detected (P<.OS) for lactic soybeans, I silages had higher (P<.Ol) silages, but ethanol concentration of acid concentration in 1989. Ensiled VFA than NI silages, and VFA concenR2 silages did not differ (P>.10) trations declined (P<.OS) with adR6 Bay soybeans had the highest vancing growth stage. As in 1988, between inoculant treatments. (P< .OS) lactic acid concentration Within NI soybeans, ethanol concen- followed by R6 Stafford silages. the greatest molar percentage of total trations increased (P<.OS) with Ensiled R6 Stafford soybeans did not VFA was present as acetic acid. advancing growth stage. Within I differ (P>.1O) in lactic acid concentra- Approximately 9S% or more of the soybeans, ethanol concentrations of tion from R2 Bay silage. Silages from total VFA produced by Bay silage was R2 silages were lower than those of present as acetic acid, and the proR4 sO)7beans '''lere intermediate in R4 and R6 silages, but ethanol lactic acid concentration, and silages portion did not differ (P>.1O) with concentrations did not differ (P>.1O) from R2 Stafford soybeans were inoculant or growth stage. Within between R4 and R6 silages. numerically lowest in lactic acid Stafford soybeans, I R4 silage numeriA growth stage x inoculant concentrations. Ammonia concentra- cally had the lowest molar percentinteraction was detected (P<.OS) for tions were higher (P<.Ol) in 1989 age of acetic acid but it was not pH and lactic acid in 1989. Silages from Stafford than from Bay silages different (P>.1 0) from that of lor NI from R4 soybeans had the highest and from R2 than from R4 and R6 R2 silages or NI R6 silages. Molar pH and I R6 silages had the lowest silages. Ethanol concentrations were proportion of propionic acid was pH. The pH of Bay silage was lower higher (P<.Ol) from Bay than from greater (P< .OS) from R4 than R6 (P< .OS) than that of Stafford silage Stafford silages and from R6 than silages but that of R2 silages did not when averaged across growth stages from R2 and R4 silages in 1989. differ from either R4 or R6 silages. and inoculant treatments. InocuCultivar x growth stage x inocuIsobutyric acid proportion was lated R6 silages contained the greatgreater (P<.OS) from R4 Stafford lant interactions were detected V _ _ _ _ _ ...I
ICGI ClIIU
" ' _ _I.L!. __ _
1 _____ 1 _ __ ....
IflUCUldfl~
Silages of Whole-Plant Soybeans
TABLE 6. Effects of soybean growth stage on quality of silages made from whole-plant soybeans (OM basis). Year and quality characteristic 1988 N NDF ADF ADL Ca p
1989 N NDF ADF ADL Ca p
Growth stage R2
R4
R6
SE
3.0a 47.8 b 38.2a 6.3 b 1.S6 .29
3.6 b Sl.0a 39.S a 7.S a 1.S2 .29
2.Sb 47.3 b 3S.4 b 7.4 a 1.41 .27
.OS .73 .62 .17 .017 .OOS
3.2a 3S.8 b 26.1c S.sc l.4S .24c
3.pb 40.P 27.9 b 6.4 b 1.42 .29 b
3.0 b 41.2a 29.S a 7.P 1.32 .32 a
.OS .40 .36 .11 .060 .007
a-
silages than the other cultivar and growth stage combinations. Molar proportion of butyric acid was low or nondetectible within Bay soybeans and did not differ (P>.10) within the various combinations of growth stage and inoculant. With the exception of I R6 and NI R4 silages, the molar proportion of butyric acid from Stafford silages were higher (P<.OS) than that from Bay silages. Inoculated R2 and R4 Stafford and NI R6 Stafford silages had greater than 10% of the total VFA produced as butyric acid. Silages from R6 soybeans had higher (P<.OS) molar percentages of valeric acid than those from R2 and R4 soybeans. McCullough (16) summarized data concerning factors affecting silage quality. Generally, lactic acid concentration is recognized as being related positively to silage quality, whereas silage pH, acetic acid, butyric acid, and ammonia N as a percentage of total N generally are recognized as being related negatively to silage quality. Stafford silages had higher N (P< .OS) and P concentrations (P<.Ol) and lower (P<.Ol) ADL than Bay silages in 1988 and higher (P<.Ol) N and P and lower (P<.Ol) NDF, ADF, and ADL than Bay silages in 1989
(Table 5). Sweeney and Granade (21) reported lower N concentrations in whole-plant soybean samples from Bay soybeans harvested at R6 than from two maturity group IV soybean cultivars (Desoto and Douglas) as well as from another maturity group V soybean cultivar (Essex). Noninoculated silages had greater (P<.OS) Ca and tended (P<.1O) to have greater P concentrations than I silages in 1988, but these differences were not observed in 1989. Nitrogen content of R2 silages was greater (P<.OS) than that of R4 and R6 silages in 1988 and of R6 in 1989 (Table 6). Hubbell et al. (11) reported 10.5 % higher crude protein content of soybean hay harvested at RS compared with that harvested at R2. Munoz et al. (17) reported relatively constant crude protein concentrations of soybean stems and petioles with advancing growth stage, but a substantial decline in leaf crude protein content from R2 through R6 growth stages. However, crude protein content of pods increased between R4 and R6 growth stages in that study. In 1988, NDF content increased (P<.OS) between R2 and R4 growth stages then declined (P<.OS) at the R6
79
growth stage. Acid-detergent fiber concentration tended to follow a similar pattern, but with a more substantial decline at R6. Aciddetergent lignin concentrations increased between R2 and R4 growth stages but did not increase further beyond the R4 growth stage in 1988. In 1989, NDF content increased (P<.OS) between R2 and R4 growth stages but did not decline between R4 and R6 growth stages as had occurred in the 1988 silages. Furthermore, ADF and ADL contents continued to increase (P<.OS) with advancing growth stage in 1989. Hubbell et al. (11) reported 10.6% lower NDF, but 4.3% higher ADF and 43.9% higher lignin from soybean hay harvested at RS compared with soybean hay harvested at R2. Calcium concentrations were not affected by growth stage at harvest in either year. Phosphorus concentrations did not differ among growth stages in 1988, but increased (P<.OS) with advancing growth stage in 1989. Sweeney and Granade (21) reported that leaf P concentrations declined with advancing growth stage through RS in Bay soybeans as well as in two maturity group IV soybean cultivars (Desoto and Douglas). However, they did not report P concentrations in the stems and pods with advancing growth stage. Munoz et al. (17) recommended that soybeans be harvested for hay at the R6 growth stage to optimize yield and quality. In this experiment, DM yields were dramatically (2.0Sx) higher at the R6 than at the R2 growth stage, but quality tended to decline with advancing growth stage. However, quality of silages produced from R6 soybeans was still acceptable (greater than 15.5% crude protein and less than 36% ADF) as a feed source for beef cattle. The laterharvested soybeans also had a lower and more ideal moisture content for ensiling. Because the objective of most soybean producers is to produce seed, producing silage from the whole plant is more of a salvage operation during adverse conditions than a planned management prac-
80
Coffey et ai.
tice. Therefore, harvesting soybeans at the R6 growth stage offers the soybean producer the option of waiting until late in the growing season before deciding whether to harvest the whole plant for hay or silage or the soybeans for seed. This delay increases the likelihood that a producer can choose the more profitable alternative.
Acknowledgments Appreciation is expressed to Chr. Hansen's Lab. for providing silage inoculant, to Bob Middleton, Charlie Middleton, Larry Ellis, Terry Green, and Joyce Erikson for assistance with planting and harvesting operations, and to Glenda Newkirk for laboratory analyses.
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10. Goering, H. K., and P. ] . Van So est. 1970. Forage fiber analyses (apparatus, reagents, procedures, and some applications) . Agric. Handbook 379. ARS, USDA, Washington, DC.
20. Snedecor, G. W., and W. G. Cochran, 1980. Statistical Methods (7th Ed.). The Iowa State Univ. Press, Ames, IA.
11. Hubbell, D.,]. M. Rakes, O. T. Stallcup, 1. B. Daniels, and K. E. Harrison. 1988. Soybean hays made from plants in bloom and pod
21. Sweeney, D. W., and G. V. Granade. 1993. Yield, nutrient, and soil sulfur response to ammonium sulfate fertilization of soybean cultivars. ] . Plant Nutr. 16:1083.
7'.J.. ...T.L._~ __LLOnlerll ._L_ ._L C'~I ,,_...1_ OT .)lIayes IVlaue r _
_.l.
__. __ ..
~Ulrlerll
from Whole-Plant Soybeans1 K. P. COFFEy2, PAS, G. V. GRANADE3, and J. L. MOYER Kansas State University - Southeast Agricultural Research Center, Parsons, KS 67357 University of Georgia,Georgia Experiment Station, Griffin, GA 30223
Abstract Whole-plant soybean forages were chopped and ensiled in 1988 and 1989 from plots in a 2 x 3 x 2 factorial arrangement of a randomized complete block design. Maturity group IV (,Stafford') vs group V ('Bay') soybean forages were harvested and ensiled at either full bloom (R2), full pod (R4), or full seed (R6) growth stages, with (1) or without (NI) a silage inoculant for a minimum of60 d in lined 19-L containers. Dry matter yield of Bay in both years and Stafford in 1989 increased (P<.OS) with advancing growth stage, and R2 and R6 Bay yields were greater (p<.OS) than R2 and R6 Stafford yields. Three-way interactions were detected (p<.OS) for silage pH; total volatile fatty acids (VFA); and molar proportions of acetic, isobutyric, and butyric acids in 1988 and of acetic and butyric acids in 1989. Silages harvested at R6 had the highest (p<.OS) lactic acid and lowest (p<.OS) ammonia concentrations in
1988 and the lowest (p<.OS) total VFA in 1989. Bay had greater ethanol and ADL and lower N concentrations in both years (p<.OS) and lower pH, ammonia, and total VFA and higher NDF and ADF in 1989 than Stafford (p<.OS). Inoculated silages had lower (P<.Ol) molar proportions of propionate in 1988 and higher (p<.01) total VFA in 1989 than NI. Silages harvested at R2 had higher N in 1988 and lower ADL in both years than those harvested at R4 and R6 (p<.OS). Neutral-detergent fiber content at R4 was higher (p<.OS) than at R2 and R6 in 1988 and higher (p<.OS) than at R2 in 1989. Considering the relative magnitude of changes in yield and quality with advancing maturity, one should delay harvesting soybeans for silage until the R6 growth stage, if possible. (Key Words: Soybean, Silage, Forage Quality, Growth Stage, Silage Inoculant.)
Introduction 1 Contribution no. 95-158-J from the Kansas Agric. Exp. Sta., Manhattan, KS, 66506.
2Kansas State University. 3University of Georgia. Reviewed by D. C. Anderson and L.
J.
Bush.
Soybeans [Glycine max (1.) Merr.] are grown in the United States primarily for seed production. Adverse weather conditions often interfere with the harvest of quality soybeans. Late spring rains, early frosts, dry summers, or combinations of these factors can occur, resulting
in reduced seed yields, small or otherwise lower quality seed, or green seed. The market price of these lower quality soybean seeds may be reduced substantially. Previous research to find alternative uses for soybeans to minimize the risk associated with adverse weather or marketing conditions have centered on its value as a hay crop (11, 17 ,19) . Although soybeans also have been intercropped with corn (4, 7) or sorghum (2, 8, 12) to improve the protein content of a subsequent silage crop, evaluation of monocultured soybeans as a silage crop has been limited. The objectives of this experiment were to determine 1) differences in quality and yield between ensiled whole-plant Stafford (maturity group IV) and Bay (maturity group V) soybeans; 2) yield and quality of silages produced by harvesting soybeans at different growth stages; and 3) the effect of a silage inoculant on quality of whole-plant soybean silages.
Materials and Methods Forty-eight four-row plots, 9.1 -m in length, having a .76-m row spacing were established in 1988 and 1989 on an area of Parsons silt loam soil. Plots were arranged in four blocks of 12 plots each in a random-
75
Silages of Whole-Plant Soybeans
ized complete block design (20). Half of the plots were seeded to a maturity group IV soybean cultivar ('Stafford'), whereas the remaining half were seeded to a maturity group V soybean cultivar ('Bay'). The center two rows from two plots of each cultivar within each block were harvested with a forage chopper at either R2, R4, or R6 growth stages (9j Table 1). The forage from one of each pair of plots within a block was inoculated (1) with .03 g/kg Biomate LP/PC® (Chr. Hansen's Lab., Inc., Milwaukee, WI) to provide 100,000 cfu of Lactobacillus plantarum and Pediococcus cerevisiae/g of forage. The forage from the remaining plot of each pair within a block was not inoculated (NI). All forages were packed into 19-L plastic containers lined with three plastic trash can liners and allowed to ferment for a minimum of 60 d. Three or four of the experimental silos were opened daily over a 13-d period at the time of feeding during a consumption study using lambs. Fresh samples (2S g) were blended with distilled water (100 ml) and allowed to stand at room temperature for 1 h and then pH was measured. One hundred milliliters of .4 N HzSO 4 was added to the solution, and the mixture was allowed to stand for 48 h. The solution then was strained through four layers of cheesecloth and stored frozen
(-20°C) prior to analysis for volatile fatty acids (VFA), lactate, ammonia, and ethanol. Another fresh silage sample was dried at SO°C and ground (1 mm) for quality analyses after allowing a minimum of 72 h for equilibration to atmospheric moisture. Sample dry matter was determined by drying overnight at lOS°C. Samples were digested in HzSO 4-HPZ (IS) and analyzed for N content by colorimetric techniques of Crooke and Simpson (6) and for P content by colorimetric techniques of Kitson and Mellon (14). Calcium concentrations were determined by atomic absorption spectrophotometry after samples were digested according to the procedures of Blancher et al. (3). Neutral-detergent fiber, ADF, and acid-detergent lignin (ADL) were determined using procedures of Goering and Van Soest (10) as modified by Jeraci et al. (13). Ammonia was determined by microdiffusion (S), and lactate according to a modified procedure of Barker and Sommerson (1). Ethanol and VFA were determined using a HewlettPackard S730A gas chromatograph having a 1.83-m Chromosorb 101packed column at 200°C, a flow rate of 60 ml/min, and a flame ionization detector temperature of 2S0°C. Yield and quality data were analyzed using SAS® (18) General Linear Models (GLM) procedures for
TABLE 1. Growth stages at which soybeans were harvested for silage (9). Growth
R2 R3 R4 RS R6 R7
stage
Definition
Flower present at node immediately below the uppermost node with a completely unrolled leaf. Pod is .S cm long at one of the four uppermost nodes with a completely unrolled leaf. Pod is 2 cm long at one of the four uppermost nodes with a completely unrolled leaf. Beans beginning to develop at one of the four uppermost nodes with a completely unrolled leaf. Pod containing full size green beans at one of the four uppermost nodes with a completely unrolled leaf. Pods yellowing; SO% of the leaves yellow; physiological maturity.
a split-plot design experiment. Year, replicate, and their interaction were included in the model as the wholeplot effects. Year and replicate effects were tested using their interaction as the error term. Subplot effects were cultivarj growth stagej inoculant; all two- and three-way interactions among cultivar, growth stage, and inoculant, and all interactions with year. Upon detection of interactions of cultivar, growth stage, or inoculant with year, the analysis was conducted within year using SAS® (18) GLM procedures for a 2 x 3 x 2 factorial arrangement of a randomized complete block design. The model consisted of effects of cultivar, growth stage, inoculant, and all interactions. Differences among treatments were tested using a protected t test (20).
Results and Discussion Interactions of year with either cultivar, growth stage, or inoculant were detected (P<.OS) for most constituents measured. Therefore, data for this study were analyzed and reported within year. Bay soybean forage had greater (P<.OS) DM content than Stafford forage at the R2 growth stage in both years, at R6 in 1988, and at R4 in 1989 (Table 2). Bay and Stafford soybean forages did not differ (P>.10) in their DM content at R4 in 1988 and at R6 in 1989. Dry matter percentage of both cultivars increased (P<.OS) with increasing growth stage in 1988 and was greater (P<.OS) for both cultivars at R6 than at R2 or R4 in 1989. Forage DM yields from Bay soybeans were greater (P<.OS) than yields from Stafford soybeans in both years at R2 and R6 growth stages. Forage DM yields from R2 Bay soybeans averaged 30% greater (P<.OS) than DM yield from R2 Stafford soybeans, and yields from R6 Bay soybeans averaged 21.9% greater (P<.OS) than DM yield from R6 Stafford soybeans. Forage DM yields from soybeans harvested at the R4 growth stage did not differ between cultivars in either year. Forage DM yields from Bay
76
Coffey et al.
TABLE 2. Dry matter percentage and yield of whole-plant soybeans harvested for silage. Stafford
R,.v
--J
Year and variable
R2
R4
R6
R2
R4
R6
SE
22Ad
29Ac
36.7a
21Ae
28.7 c
31.5 b
.31
16.6c 3.7 c
19.5 b 5.7 b
21.sa . 7.9 a
. 13Ad 2.9 d
19.7 ab 5.7 b
19.0 b 6.0 b
.66 .20
Divi, 0/0
.... '" 1 h £:1.1-
""' ....... h £.J."t-
26.3 2
""1 ... r £ I."t-
£ 1.£ -
.... 1
2s.sa
.:1V
Yield, mg/ha Fresh DM
17.8d 4.1d
22.8 c 5.3 c
29.5 a 7.7 a
14Ae
24.7 bc 5.2c
26.3 b 6.8 b
.75 .17
1988 DM,% Yield, mg/ha Fresh
DM 1989
3.1 e
.... ,.
..,,,
a-eMeans within a row with no common superscript differ (P<.05).
TABLE 3. Silage characteristics from ensiled whole-plant soybeans with (I) or without (NI) an inoculant. Stafford
Bay Year and characteristic 1988 pHf Lactic9, %
I NI I NI
Ammoniag, %
i
ETOHhi, %
NI I NI
1989 pH hi Lactichi, %
I NI I N!
Ammonia 9i, % ETOH9 i, %
I NI I NI
R2
R4
R6
5.6 bc 5.9a 1.5 .7 .5 7 .69 .04 .10
5.2e 5.7 ab .8 .8 .38 .57 .28 .34
4.7f 4.61 5.0 4.9 .i 9 .26 .24
5.1 5.1 .8 1.2 .13
5.2 5.3 .6 1.0
4.8 5.0 2.6 1.9
.11 .26 .09
041
.11
.11
.10 .24 .16
.10 .63 .77
a-eMeans within an item with no common superscript differ (P<.05). fCultivai x giOwth stage x inoculant (P<.05). gGrowth stages differed (P<.05). hGrowth stage x inoculant (P<.05). iCultivars differed (P<.01). iCultivar x growth stage (P<.01).
R6
R2
R4
5.7 abc
5.6 bc 5.8 ab .5 .5 .58 .58 .06 .23
4.9f 5.2 de 2.7 3.6 .25 .35 .18
5.8 5.5 .6 1.0 .16 .09 .06 .04
4.9 5.3 1.5 1.1
5Acd
.9 1.5 .62 .51 .01 .01 5.5 SA A .4
.17 .16 .08 .09
SE
.09 .60
.058 .046
041
.10 .22
.11
.016
.13 .38 .61
.113
77
Silages of Whole-Plant Soybeans
TABLE 4. Volatile fatty acid (VFA) concentrations from ensiled whole-plant soybeans with (I) or without (NI) an inoculant. Stafford
Bay
R2
Year and VFA
1988 Total VFAe, IJmol/g DM
I NI
870.3 cde 1218.7 ab
R4
R6
R2
889.2bcd 735.1 cde
638.5 de 532.2e
1023.6abc 1052.6abc
R4
R6
SE
959.3 bcd 1322.13
984.4 abcd 539.5 e
120.84
79 .2 cde 62.3 1 5.2 7.7 1.9 bc S.2a 13.0abc 20.7 a .0 1.9 .7 2.2
98.4 a 80.6 bcde .0 2.3 .Od .3 cd .Od 13.0abc .7 1.3 .9 2.5
4.25
(mo1 / 100 mol)
Acetie e Propionicl9 Isobutyriee Butyrice Isvaleric Valerie 1989 Total VFA9 hi, IJmol/g DM
I NI I NI I NI I NI I NI I NI I NI
89.6 abc 71.5 ef 3.1 4.7 .6 bcd 1.7bcd 4.8 cd 20.8 a .S .6 1.4 .6 1319.S 1124.7
91.4 abc 77.0 de .9 3.7 .Od 1.2bcd 5.7 bcd 14.7 ab 1.1 2.7 .9 .6 1085.6 861 .6
98.8 a 91.7 ab .2 .4 .Od .Od .Od 1.3d .5 4.9 .S 1.7 641.7 704.2
88.5 abcd 90.13bc 4.0 3.2 2.1 ab .6 bcd S.4 cd S.ocd .0 .8 .0 .4 1609.7 1S07.1
1493.9 1188.3
908.7 826.2
.83 .61 3.19 1.41 .91
80.15
(mol/l 00 mol) Acetic e Propionie i Isobutyric! Butyriee Isovaleric Valeric i
I NI I NI I NI I NI I NI I NI
96.2a 94.9 ab 3.3 3.3 .0 .1 .Oc 1.F .0 .0 .5 .S
94.8 ab 9S.4 a 2.2 3.1 .0 .0 2.Sbc .Oc .0 .0 .S loS
9S .3a 96.9 a 2.4
1.1 .0 .0 .Oc .Oc .0 .0 2.2 2.0
83.8 cd 8S.8 bcd 3.0 3.2 .6 1.4 11.9a 8.6 ab .0 .0 .8 1.0
76.6 d 91.6 abc 6.7 3.1 3.1 1.5 12.5 a 2.9 bc .1 .0 .9 .9
96.Sa 83.1 cd 2 .3 1.3 .0 .0 .Oc 14.13 .0 .0 1.2 loS
3.26 1.04 .S6
2.34 .02 .40
a-dMeans within an item with no common superscript differ (P<.OS). eCultivar x growth stage x inoculant (P<.OS). fCultivar x growth stage (P<.01). 91noculated silages differed (P<.01) from noninoculated silages. hCultivars diffe red (P<.01). iGrowth stages differed (P<.OS).
soybeans in both years and Stafford soybeans in 1989 increased (P< .OS) with advancing growth stage. Ensiled R6 Bay and Stafford soybeans averaged 2.03 an d 2.13 times the DM yield of R2 Bay and Stafford soybeans, respectively. Munoz et al. (17)
reported similar increases in wholeplant soybean yield with advancing growth stage through R7. Cultivar x growth stage x inoculant interaction s were detected (P<.OS) in 1988 for silage pH (Table 3). Silages having the lowest pH were
I and NI R6 Bay and I R6 Stafford soybeans. Noninoculated R2 and R4 Bay and R4 Stafford and I R2 Stafford silages tended to have the highest pH. Lactic add concentrations were greater (P<.OS) and ammonia concentrations lower (P<.OS) from R6 silages
78
Coffey et ai.
(P<.OS) in 1988 for total VFA and molar percentages of acetic, TABLE 5. Effects of cultivar and silage inoculant on quality of silages and butyric acids (Table isobutyric, made from whole plant soybeans (OM basis) . 4) . Total VFA were numerically \...UllIVcU lowest in 1988 from Ni R6 Bay and quality Stafford silages and numerically characteristic Stafford SE NI SE Bay highest from NI R4 Stafford silage. The greatest molar percentage of total 1988 VFA was present as acetic acid in Na 2.7 2.8 .04 2.7 2.7 .04 both years. In 1988, molar percentNDF 48.3 49.2 .59 48.5 48.9 .61 age of acetic acid was numerically ADF .51 38.1 37.3 37.5 37.9 .51 highest from the I R6 silages and ADLb 7.4 6.8 .14 7.0 7.2 .14 numerically lowest from NI R4 Cac 1.49 1.50 .014 1.46 1.54 .014 pbd Stafford silage. Noninoculated silages .27 .29 .004 .27 .29 .004 1989 had greater (P<.Ol) molar proporNb 3.0 3.3 .04 3.1 3.2 .04 tions of propionic acid than I silages NDFb 39.7 38.3 39.3 .33 38.8 .33 when averaged across cultivars and ADFb 28.3 27.3 .29 28.0 27.6 .29 growth stages. Ensiled R4 Stafford ADLb 6.7 6.0 .09 6.4 6.3 .09 soybeans had the highest (P<.OS) and Ca 1.36 1.43 .049 1.38 1.4 1 .049 R6 silages the lowest (P<.OS) molar pb .31 .26 .005 .29 .28 .005 proportion of propionic acid. Molar proportions of isobutyric and butyriC aSiiages made from Bay soybeans differed (P<.05) from silages made from acids tended to be lowest from I R6 Stafford soybeans. Bay and Stafford silages and from NI bSilages made from Bay soybeans differed (P<.01) from silages made from Bay R6 silage. Butyric acid tended to Stafford soybeans. be highest from NI R2 Bay and R4 clnoculated silages differed (P<.05) from noninoculated silages. Stafford silages. Isovaleric and valeric dlnoculated silages differed (P<.1 0) from noninoculated silages. acid molar percentages did not differ (P>.1O) among cultivars, growth stages, or inoculant treatments in est (P< .OS) concentrations of lactic than from R2 or R4 silages. Bay 1988. acid, NI R6 silages were intermediate, No interactions were detected for silage had greater (P< .Ol) ethanol total VFA in 1989. Ensiled Stafford concentrations than Stafford silage. and all R2 and R4 silages had the Inoculated R4 and R6 silages had soybeans had greater (P<.Ol) VFA lowest lactic acid concentrations. A reduced (P<.OS) ethanol concentraconcentrations than ensiled Bay cultivar x growth stage interaction tions compared with NI R4 and R6 also was detected (P<.OS) for lactic soybeans, I silages had higher (P<.Ol) silages, but ethanol concentration of acid concentration in 1989. Ensiled VFA than NI silages, and VFA concenR2 silages did not differ (P>.10) trations declined (P<.OS) with adR6 Bay soybeans had the highest vancing growth stage. As in 1988, between inoculant treatments. (P< .OS) lactic acid concentration Within NI soybeans, ethanol concen- followed by R6 Stafford silages. the greatest molar percentage of total trations increased (P<.OS) with Ensiled R6 Stafford soybeans did not VFA was present as acetic acid. advancing growth stage. Within I differ (P>.1O) in lactic acid concentra- Approximately 9S% or more of the soybeans, ethanol concentrations of tion from R2 Bay silage. Silages from total VFA produced by Bay silage was R2 silages were lower than those of present as acetic acid, and the proR4 sO)7beans '''lere intermediate in R4 and R6 silages, but ethanol lactic acid concentration, and silages portion did not differ (P>.1O) with concentrations did not differ (P>.1O) from R2 Stafford soybeans were inoculant or growth stage. Within between R4 and R6 silages. numerically lowest in lactic acid Stafford soybeans, I R4 silage numeriA growth stage x inoculant concentrations. Ammonia concentra- cally had the lowest molar percentinteraction was detected (P<.OS) for tions were higher (P<.Ol) in 1989 age of acetic acid but it was not pH and lactic acid in 1989. Silages from Stafford than from Bay silages different (P>.1 0) from that of lor NI from R4 soybeans had the highest and from R2 than from R4 and R6 R2 silages or NI R6 silages. Molar pH and I R6 silages had the lowest silages. Ethanol concentrations were proportion of propionic acid was pH. The pH of Bay silage was lower higher (P<.Ol) from Bay than from greater (P< .OS) from R4 than R6 (P< .OS) than that of Stafford silage Stafford silages and from R6 than silages but that of R2 silages did not when averaged across growth stages from R2 and R4 silages in 1989. differ from either R4 or R6 silages. and inoculant treatments. InocuCultivar x growth stage x inocuIsobutyric acid proportion was lated R6 silages contained the greatgreater (P<.OS) from R4 Stafford lant interactions were detected V _ _ _ _ _ ...I
ICGI ClIIU
" ' _ _I.L!. __ _
1 _____ 1 _ __ ....
IflUCUldfl~
Silages of Whole-Plant Soybeans
TABLE 6. Effects of soybean growth stage on quality of silages made from whole-plant soybeans (OM basis). Year and quality characteristic 1988 N NDF ADF ADL Ca p
1989 N NDF ADF ADL Ca p
Growth stage R2
R4
R6
SE
3.0a 47.8 b 38.2a 6.3 b 1.S6 .29
3.6 b Sl.0a 39.S a 7.S a 1.S2 .29
2.Sb 47.3 b 3S.4 b 7.4 a 1.41 .27
.OS .73 .62 .17 .017 .OOS
3.2a 3S.8 b 26.1c S.sc l.4S .24c
3.pb 40.P 27.9 b 6.4 b 1.42 .29 b
3.0 b 41.2a 29.S a 7.P 1.32 .32 a
.OS .40 .36 .11 .060 .007
a-
silages than the other cultivar and growth stage combinations. Molar proportion of butyric acid was low or nondetectible within Bay soybeans and did not differ (P>.10) within the various combinations of growth stage and inoculant. With the exception of I R6 and NI R4 silages, the molar proportion of butyric acid from Stafford silages were higher (P<.OS) than that from Bay silages. Inoculated R2 and R4 Stafford and NI R6 Stafford silages had greater than 10% of the total VFA produced as butyric acid. Silages from R6 soybeans had higher (P<.OS) molar percentages of valeric acid than those from R2 and R4 soybeans. McCullough (16) summarized data concerning factors affecting silage quality. Generally, lactic acid concentration is recognized as being related positively to silage quality, whereas silage pH, acetic acid, butyric acid, and ammonia N as a percentage of total N generally are recognized as being related negatively to silage quality. Stafford silages had higher N (P< .OS) and P concentrations (P<.Ol) and lower (P<.Ol) ADL than Bay silages in 1988 and higher (P<.Ol) N and P and lower (P<.Ol) NDF, ADF, and ADL than Bay silages in 1989
(Table 5). Sweeney and Granade (21) reported lower N concentrations in whole-plant soybean samples from Bay soybeans harvested at R6 than from two maturity group IV soybean cultivars (Desoto and Douglas) as well as from another maturity group V soybean cultivar (Essex). Noninoculated silages had greater (P<.OS) Ca and tended (P<.1O) to have greater P concentrations than I silages in 1988, but these differences were not observed in 1989. Nitrogen content of R2 silages was greater (P<.OS) than that of R4 and R6 silages in 1988 and of R6 in 1989 (Table 6). Hubbell et al. (11) reported 10.5 % higher crude protein content of soybean hay harvested at RS compared with that harvested at R2. Munoz et al. (17) reported relatively constant crude protein concentrations of soybean stems and petioles with advancing growth stage, but a substantial decline in leaf crude protein content from R2 through R6 growth stages. However, crude protein content of pods increased between R4 and R6 growth stages in that study. In 1988, NDF content increased (P<.OS) between R2 and R4 growth stages then declined (P<.OS) at the R6
79
growth stage. Acid-detergent fiber concentration tended to follow a similar pattern, but with a more substantial decline at R6. Aciddetergent lignin concentrations increased between R2 and R4 growth stages but did not increase further beyond the R4 growth stage in 1988. In 1989, NDF content increased (P<.OS) between R2 and R4 growth stages but did not decline between R4 and R6 growth stages as had occurred in the 1988 silages. Furthermore, ADF and ADL contents continued to increase (P<.OS) with advancing growth stage in 1989. Hubbell et al. (11) reported 10.6% lower NDF, but 4.3% higher ADF and 43.9% higher lignin from soybean hay harvested at RS compared with soybean hay harvested at R2. Calcium concentrations were not affected by growth stage at harvest in either year. Phosphorus concentrations did not differ among growth stages in 1988, but increased (P<.OS) with advancing growth stage in 1989. Sweeney and Granade (21) reported that leaf P concentrations declined with advancing growth stage through RS in Bay soybeans as well as in two maturity group IV soybean cultivars (Desoto and Douglas). However, they did not report P concentrations in the stems and pods with advancing growth stage. Munoz et al. (17) recommended that soybeans be harvested for hay at the R6 growth stage to optimize yield and quality. In this experiment, DM yields were dramatically (2.0Sx) higher at the R6 than at the R2 growth stage, but quality tended to decline with advancing growth stage. However, quality of silages produced from R6 soybeans was still acceptable (greater than 15.5% crude protein and less than 36% ADF) as a feed source for beef cattle. The laterharvested soybeans also had a lower and more ideal moisture content for ensiling. Because the objective of most soybean producers is to produce seed, producing silage from the whole plant is more of a salvage operation during adverse conditions than a planned management prac-
80
Coffey et ai.
tice. Therefore, harvesting soybeans at the R6 growth stage offers the soybean producer the option of waiting until late in the growing season before deciding whether to harvest the whole plant for hay or silage or the soybeans for seed. This delay increases the likelihood that a producer can choose the more profitable alternative.
Acknowledgments Appreciation is expressed to Chr. Hansen's Lab. for providing silage inoculant, to Bob Middleton, Charlie Middleton, Larry Ellis, Terry Green, and Joyce Erikson for assistance with planting and harvesting operations, and to Glenda Newkirk for laboratory analyses.
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2. Baxter, H. D., M.]. Montgomery, and]. R. Owen. 1984. Comparison of soybean-grain sorghum silage with corn silage for lactating cows.]. Dairy Sci. 67:86. 3. Blancher, R. W., G. Rehm, and A. C. Caldwell. 1965. Sulfur in plant materials by digestion with nitric and perchloric acids. Soil Sci. Soc. Am. Proc. 29:71. 4. Christosov, A. 1972. Influence of the plant density in post-harvest maize-soybean mixed crops upon the yield and feed value of silage. Plant Sci. 9: 136. 5. Conway, E.]. 1963. Microdiffusion Analysis and Volumetric Error. Chemical Publishing Co., New York, NY. 6. Crooke, W. M., and W. E. Simpson. 1971. Determination of ammonium in Kjeldahl digests of crops by an automated procedure. ]. Sci. Food Agric. 22:9. 7. Daniel, P., and P. Romer. 1988. The influence of the admixture of Andean lupin silage (Lup/nus mutabilis 1.) and soybean silage (Glycine soja (1.) Sieb. et Zucc.) to crude protein content, feeding value and quality of maize silages. Landv~rtsch . Forsch. 41 :13 1. 8. Elmore, R. w., and]. A. ]ackobs. 1986. Yield and nitrogen yield of sorghum intercropped with nodulating and nonnodulating soybeans. Agron. ]. 78:780. 9. Fehr, W. R., C. E. Caviness, D. T. Burmood, and]. S. Pennington. 1971. Stage of development descriptions for soybeans, Glycine max (1.) Merrill. Crop Sci. 11:929.
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