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Forage sorghum silage dry matter disappearance as influenced by plant part proportion
Animal Feed Science and Technology, 33 ( 1991 ) 313-322
313
Elsevier Science Publishers B.V., Amsterdam
Forage sorghum silage dry matter disappearance as influenced by plant part proportion 1 J.S. White a, K.K. Bolsen b, G. Posleff and J.W. NeilP aAnimal Nutrition Inc., 6608 W. Main, Belleville, IL 62223, USA bDepartment of Animal Science and Industry, Kansas State University, Manhattan, KS 66506, USA CDepartment of Agronomy, Kansas State University, Manhattan, KS 66506, USA dDepartment of Statistics, Kansas State University, Manhattan, KS 66506, USA (Received 16 December 1989; accepted 15 October 1990)
ABSTRACT
White, J.S., Bolsen, K.K., Posler, G. and Neill, J.W., 1991. Forage sorghum silage dry matter disappearance as influenced by plant part proportion. Anim. Feed Sci. Technol., 33:313-322. Forage sorghum (Sorghum bicolor (L.) Moench) is widely grown for silage in the High Plains region of the U.S.A. The in vitro dry matter disappearance (IVDMD) dynamics of forage sorghum silage, as influenced by the proportion of ensiled plant parts, were examined. Five mid- to late-season forage hybrids were grown at Manhattan, Kansas, on a Smolan silty clay loam (fine, montmorillonitic, mesic Typic Agriustoll) in 1987. The hybrids were harvested at the hard dough stage of maturity. Grain yields ranged from 4.18 to 5.23 Mg ha -I, and silage yields from 13.72 to 16.45 Mg ha -~. At ensiling, five plants per hybrid were separated into grain, leaf, sheath and stalk parts, chopped, put into nylon bags and ensiled with their respective silages in pilot silos. The distribution of dry matter (g kg-~ ) among the plant parts was grain 282-413, leaf 208-229, sheath 107-170, stalk 195-401. The pH of each silage and plant part was determined at silo opening. The IVDMDs of plant parts were grain 769, leaf 577, sheath 527 and stalk 608 g kg -~, and ranged from 582 to 617 g kg -~ for silages. For each silage, each plant part was individuallyincreased to unity, then the IVDMD dynamics were plotted. The silages were reconstituted and the IVDMD determined. These ranged from 633 to 677 g kg-t. Statistically, the reconstituted silage IVDMD is the sum of the plant part IVDMD values, but the actual silage IVDMD was not. Regression equations were generated to predict silage IVDMD based on the proportion of plant parts for each hybrid. Grain had the greatest and a positive effect on silage IVDMD dynamics, whereas the sheath component had a negative effect.
INTRODUCTION
HistoricaUy, Kansas has been the leading state in forage sorghum (Sorghum bicolor (L.) Moench) silage production. Advantages of sorghum for silage compared to corn (Zea mays (L.) ) include: ( l ) lower production costs; (2) ~Journal contribution No. 89-220-J from the Kansas Agriculture Experiment Station, Manhattan, Kansas.
0377-8401/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
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J.S. WHITE ET AL.
greater drought tolerance (Beadle et al., 1973; Stout and Simpson, 1978); ( 3 ) greater ability to recover from drought (Sanchez-Diaz and Kramer, 1971 ); (4) high yield potential under dryland conditions (Cummins, 1981 ); (5) higher crude protein content (Kirch et al., 1987, 1988; White et al., 1988a). Earlier studies have indicated that grain sorghum silage is nutritionally superior to forage sorghum silage. Rupp et al. (1975 ) compared the silage of grain and forage sorghum hybrids in a digestion trial and found that the grain sorghum silage had greater in vivo digestibility than did forage sorghum silage, and that the whole-seed disappearance was the same. The voluntary intake of silage by livestock is greater for grain sorghum silage than forage sorghum silage (Kirch et al., 1987, 1988; White et al., 1988a). Kansas trials have indicated that only high-grain-producing forage sorghum hybrids approach the feeding value of grain sorghum hybrids when they are fed as silage. While some high-yielding forage sorghum hybrids match grain sorghum hybrids in grain production, the forage to grain ratio is greater. White et al. (1988b) evaluated 80 forage sorghum cultivars and found that some non-grain-producing hybrids had the highest in vitro dry matter disappearance (IVDMD). Earlier work in Arkansas (Thurman et al., 1960) compared forage sorghum cultivars and noted that the male sterile hybrid RS 310 had the highest digestibility. Pederson et al. (1982) compared the quality and agronomic traits of 49 forage sorghum hybrids and suggested that the most rapid way to improve the quality of forage sorghum forage would be to improve IVDMD. In vitro dry matter disappearance is deemed an adequate measure of digestibility in that Marten et al. (1975), Wanapat et al. (1986) and earlier work in our laboratory (White et al., 1988a,b) have shown a high correlation between IVDMD and in vivo apparent dry matter (DM) digestibility. This experiment was conducted specifically to examine the influence of the grain fraction on the IVDMD of forage sorghum silage. It was hypothesized that the IVDMD of the silage would be the sum of the IVDMD of the ensiled plant parts. The objectives of this experiment were to: ( 1 ) monitor the dynamics of IVDMD as different ensiled plant parts were altered to comprise varying proportions of the silage DM; (2) develop regression equations to predict the silage IVDMD of forage sorghum hybrids based on plant part ratios; (3) determine which plant part (s) would be most useful as selection criteria when selecting for silage digestibility. MATERIALS AND METHODS
Five mid- to late-season forage sorghum hybrids were planted on 3 June 1987 and grown under dryland conditions (precipitation: 1 January-3 June, 328 ram, 3 June-15 October, 247 ram; data from weather library, Kansas State University, Manhattan, KS) on a Smolan silty clay loam soil (fine,
PLANTPARTPROPORTIONANDSORGHUMSILAGEDM DISAPPEARANCE
315
montmorillonitic, mesic, Typic Argiustoll) near the Kansas State University campus, Manhattan. The hybrids included were Cargill 455, DeKalb 25-E, Funk's 102F, Golden Acres-TE Silomaker and Northrup King 300 a. One month prior to planting, l 10 kg h a - ~of anhydrous ammonia were applied. A pre-plant soil test indicated that phosphorus and potassium were adequate. Carbofuran a ( 1.12 kg h a - i active ingredient (a.i.)) was applied in the furrow at planting and atrazine (2.25 kg ha-1 a.i.) was used as the pre-plant herbicide. Dimethoate (0.56 kg ha-~ a.i. ) was used to control greenbugs, spider mites and grasshoppers. A randomized complete block design with three replications was used, with each plot containing six rows 76 cm apart and 60 m in length. All plots were harvested at the hard dough stage (growth Stage 8 of Vandedip and Reeves, 1972). The stage of maturity was determined by visual and physical evaluation of several heads per plot. Silage yield was determined by harvesting three inside rows of each plot with a precision forage chopper. Grain yield was determined by clipping all heads from a random 18.3-cm section of the remaining inside row of each plot and threshing the heads in a stationary thresher. Three subsamples of five plants each were taken from the remaining inside row at harvest to determine plant part ratios. Plants were cut 5 cm above the soil surface, separated into grain, leaf blade (removed at the collar), sheath (removed at the node) and stalk parts. Separated materials were manually chopped to ~ 1 cm in length. Samples containing 100300 g of separate plants were then placed in nylon bags with a pore size of I mm. The nylon bags containing the plant part samples were ensiled along with their respective silages in plastic-lined, 210-1 pilot silos. Two pilot silos were used for each hybrid. The silos were stored at ambient temperature for 120-135 days prior to opening. At opening, the nylon bags were recovered for chemical analyses of samples. The pH was determined on the individual plant part samples and the surrounding silage. A sample of the plant material was diluted in ten times its weight of distilled water, mixed and allowed to equilibrate for 1.5 h prior to determining pH with an Orion Research Digital Ionalyzer 50 I. All pH samples were measured in duplicate. Samples were dried in a forced-air oven at 55 °C for 72 h and then ground in a Wiley mill to pass a l-mm screen. The IVDMD of each silage sample was determined in triplicate with a modified Tilley and Terry ( 1963 ) procedure. The modifications were the use of tared, oven-dry centrifuge tubes, deletion of the HgC1 solution and digesting samples in acid-pepsin for 40 h; 5% of each run were blanks to account aThe use of trade name products or identification of proprietary hybrids is for clarity in communication and to ensure the ability of other researchers to duplicate the study. It does not constitute an endorsement of those products and hybrids by the Kansas Agriculture Experiment Station, nor does it imply that similar products are not acceptable for a similar use.
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for the microbial yield of the procedure. To determine IVDMD dynamics for sorghum hybrids having different proportions of plant parts, each silage and each plant part within a silage were combined in such a way that the samples had a specific plant part increased in 50-rag increments from the initial infield proportion (silage) to 1.0, in 50-mg increments. These samples were adjusted to weigh 500 mg ofDM + 10 mg and were digested in duplicate. The IVDMD of each silage and plant part of the respective hybrids was determined in triplicate. Using plant part ratio data, the silages of the hybrids were reconstituted using the ensiled plant parts. The reconstituted silage IVDMD was determined in triplicate. The summation IVDMD of a hybrid was calculated by multiplying the proportion of the DM per part by the IVDMD of the respective part, and then adding the four values. Data were statistically analyzed with analysis of variance procedures using the General Linear Model of the Statistical Analysis Systems (S.A.S.) (S.A.S., 1985). The regression equations were generated by S.A.S. (1985) using the stepwise procedure. DISCUSSION
Agronomic data for the five forage sorghum hybrids are shown in Table 1. The hybrids reached half-bloom 71-77 days after planting and were harvested 108-118 days after planting (data not shown). The hybrid Silomaker had the lowest grain yield and NK 300 had the lowest silage yield. There were no significant differences among the hybrids for proportion of DM as leaf or sheath. The hybrid DeKalb 25-E had the highest proportion of stalks and the highest forage to grain ratio. The plant subsamples taken for determining plant part proportions agreed well, i.e. within 5 percentage units, with the harvest data for four out of the five hybrids. It appears that the use of subsamples to TABLE 1 Dry m a t t e r yields ( M g h - ~) a n d plant parts ( g kg - t D M ) for five forage s o r g h u m h y b r i d s Hybrid
D M yield
Plant part
Grain
Silage
Grain
Leaf
Sheath
Stalk
Cargill 455 D e K a l b 25-E F u n k ' s 102F G A - T E Silomaker N K 300
5. I a 4.9 a 5.2 ~ 4.2 5.0 a
15.7 *'c 16.4 a'¢ 14.7 a'b 14.2 b 13.7
372 a'b 282 a 374 ~'b 399 ~'b 413 b
208 210 210 215 229
124 107 127 133 170
295 bx 401 d 289 b'c 253 Lb'c 195 a'b
SE
0.17
0.40
44.2
17.8
M e a n s in a c o l u m n w i t h o u t the s a m e superscript differ significantly ( P < 0.05).
19.9
23.0
PLANT PART PROPORTION AND SORGHUM SILAGE DM DISAPPEARANCE
317
determine grain proportion may overestimate the proportion of grain in the crop. All silages and plant parts were well preserved, as indicated by the terminal pH values (Table 2) and no observed spoilage or off odors. The pH values of the grain were the highest. Schake et al. ( 1982 ) ensiled sorghum plant parts and reported that volatile fatty acid production during the fermentation process was much lower for the head plant part than for leaf or stalk parts. The pH values of the plant parts are taken as evidence that the bagged plant parts did undergo a fermentation and were successfully ensiled. There were significant differences among hybrids for IVDMD of all parts (Table 3). For all hybrids, the grain component had the greatest IVDMD, whereas the sheath had the lowest. Thurman et al. (1960) reported that the leaf of Atlas forage sorghum had the highest digestibility and suggested that TABLE2 Silage a n d plant part p H values for five forage s o r g h u m h y b r i d s Hybrid
Silage
Plant part Grain
Leaf
Sheath
Stalk
Cargill 455 D e K a l b 25-E F u n k ' s 102F G A - T E Silomaker N K 300
4.06 c 3.88 ~ 4.07 c 3.98 b 4.06 c
4.32 a'b 4.42 a 4.36 a'b'~ 4.41 b'c 4.68 d
4.18 ¢ 4.04 a 4.22 d 4.28 ~ 4. l0 b
4.02 b 3.97" 4.26 d 4.16 c 4.06 b
4.10 b 3.80" 4.16 c 4.14 b'c 4.24 d
SE
0.011
0.017
0.010
0.012
0.013
M e a n s in a c o l u m n w i t h o u t t h e s a m e superscript differ significantly ( P < 0.05 ).
TABLE 3 Plant part I V D M D (g k g - i ) for five forage s o r g h u m h y b r i d s Hybrid
P l a n t part Grain
Leaf
Sheath
Stalk
Cargill 455 D e K a l b 25-E F u n k ' s 102F GA-TE Silomaker N K 300
724 "w 775 b,w 782 b,w 773 b,w 792 b'w
566 a'y 614 c'x 565 a'b,y 601 b.c,y 540 a'y
490 a,z 542 b.y 532 a,y 572c.z 496 a'z
608 b'x 604 b'x 552 ~'y 653c.~ 622 b'x
Mean SE
769 10.3
577 10.3
527 10.3
608 10.3
a'b'CMeans in a c o l u m n w i t h o u t the s a m e superscript differ significantly ( P < 0.05). w'~'Y'ZMeans in a row w i t h o u t the s a m e superscript differ significantly ( P < 0.05).
J.S. WHITE ET AL.
318
forage sorghum silage quality could be improved by the development of leafy hybrids (Thurman et al., 1964). Our data suggest that increasing the grain proportion of forage sorghum would improve silage digestibility to a greater extent than increasing the leaf proportion in improved forage sorghum hybrids. Increasing the proportion of a plant part in silage samples gave an IVDMD response (shown in Figs. 1-4). For all silagcs, plotting IVDMD against increasing proportions of grain produced a positive response (Fig. 1 ), whereas plotting IVDMD against the proportion of sheath gave a negative response (Fig. 2). Plots of IVDMD against proportion of leaf (Fig. 3 ) and stalk (Fig. 4 ) produced less variation than did plots of IVDMD against grain or sheath. Silage chemical composition differed (Table 4). The hybrids had similar
. . . . ..... - ---
800 -
....
25 E 102 F 455 - SILOMAKER
J"
NK,~o
..-"
700
--"
. ~. ~':-~"
. --.5~
,'~~ ./:'.." ...... ... /.:,.-"
600
500 I 100
I 200
I 300
I 400
[ 500
I 600
I 700
I 800
I 900
I 1000
g grain kg-1 sample
Fig. 1. Effect on IVDMD of increasing the proportion of grain in the silage samples.
800
"
. . . . .... .... . . . .
25 E 102F 455 SILOMAKER NK300
c•70O 2_ ol
a
:E 600
......
~ - - - f -" "_ - . ~ - ~ " -
S00 I 100
I 200
I 300
I 400
I S00
I S00
I 700
I 800
i 900
I 1000
g l e a f k g - 1 sample
Fig. 2. Effect on IVDMD of increasing the proportion of leaf in the silage samples.
PLANT PART PROPORTION AND SORGHUM SILAGE DM DISAPPEARANCE
800 -
319
25 E 102 F 455 SILOMAKER NK300
. . . . ..... .... . . . .
5700 oi
c~ :E
~ 60o S00 I
I
I
I
I
I
I
I
I
I
100 20o 3oo 4oo 5oo 6oo 7oo 800 90o lOOO g sheath kg-1 sample
Fig. 3. Effect on IVDMD of increasing the proportion of sheath in the silage samples.
800
L .... ..... .... . . . .
25 E 102 F 455 $1LOMAKER NK300
57oo
L :E
._.
L
:__. _. --- -_-.-_----
;--..
500
I 100
20l) 31~0 440 soo ' s~o 7~0 s~o 90o ' 10100 g stalk kg-1 sample
Fig. 4. Effect on IVDMD of increasing the proportion of stalk in the silage samples.
crude protein and ash contents. Significant differences were observed for neutral detergent fiber (NDF), ether extract, acid detergent fiber (ADF) and permanganate lignin. Non-structural carbohydrates (NSC) were calculated after Noeek and Russell ( 1988 ). Higher NSC values did not consistently give higher IVDMD. Wilkinson and Phipps (1979) found only small differences among silage in vitro digestibilities of three similar corn varieties. Likewise, we observed small differences among the silage IVDMD, but significant differences among plant part IVDMD. Cummins (1981 ) compared four forage sorghum hybrids and showed greater IVDMD for the stalk than for the leaf plant part. These data indicate that the IVDMD of the forage sorghum silage is not the
J.S. WHITE ET AL.
320 TABLE 4 Silage chemical composition (g kg- t DM) of the five forage sorghum hybrids Hybrid
Crude protein
NDF
Ether extract
Ash
NSC*
ADF
Lignin
Cargill 455 DeKalb 25-E Funk's 102F GA-TE Silomaker NK 300
78 73 74 73 77
558 d 531 c 496 a'b 518 b'c 476"
30 b 24 a 27 a'b 32 b 31 b
67 63 61 61 69
307 a 349 b 379 c'd 353 b'c 388"
347 ~'b 366 b 339 ~'b 320" 333"
45 a'b 57 ~ 45 ~'b 40" 52 b'c
Mean SE
75.0 5.0
515.8 12.2
28.8 2.5
64.2 4.0
355 12.6
341.0 9.8
47.8 6.3
Means in a column without the same superscript differ significantly ( P < 0.05).
TABLE 5 Disappearance of silage, reconstituted silage, and sum of plant parts for five forage sorghum hybrids (gkg -~ ) Hybrid
IVDMD
Cargill 455 DeKaib 25-E Funk's 102F GA-TE Silomaker NK 300 SE
Silage
Reconstituted silage
Sum of parts
584 b'y 582 b'y 588 b'y 615 a'y 617 a'y
633 b,z 664 a,~ 634 b,~ 677 ~'z 639 b'~
628 a,z 648 b.... 638 ~'a'z 679 a'~ 656 b'~
2.38
6.62
5.10
a,bMeans in a column without the same superscript differ significantly ( P < 0.05 ). Y'ZMeans in a row without the same superscript differ significantly ( P < 0.05).
TABLE 6 Regression equations for predicting silage IVDMD for five forage sorghum hybrids Hybrid
Cargill455 DeKalb 25-E Funk's 102F GA-TE Silomaker NK 300
Intercept
549 552 509 532 508
Slope Grain
Leaf
Sheath
Stalk
145 191 272 201 304
24 37 -
-78 -40 -19
16 2 11 93
SE
R2
4.9 10.3 7.7 14.0 10.4
0.97 0.89 0.95 0.77 0.95
PLANTPARTPROPORTIONANDSORGHUMSILAGEDM DISAPPEARANCE
321
sum of the plant part IVDMDs. However, given the large variation in plant part proportion between plants, within plots and between plots, there is great potential for sampling error. Van Soest (1982) suggested another potential reason for the observed non-additivity: "Rumen bacteria are partially digestible and the comparability of in vivo to in vitro digestibility value rests on the fact that ruminant feces are composed of roughly equivalent amounts of undigested cell wall and bacteria remnants similar to those obtained in the in vitro situation". Van Soest also indicates that the difference between apparent and true digestibility in vitro is on the order of 11.5 units of digestibility, whereas in vivo the difference is 13.9 units of digestibility. In our study, the reconstituted silage IVDMD was statistically equivalent to the sum of the plant part IVDMDs (Table 5 ). There seemed to be some associative effect, i.e. a non-linear IVDMD response, when plant parts were blended to reconstitute a silage. The proportion of grain in the ideal forage sorghum hybrid for silage is limited by such associative effects. Hart (1987) demonstrated that 15-30% grain in a sorghum grain and silage-based diet improved the digestibility and dry matter intake of cattle, but higher proportions of grain (45-60%) did not result in further increases in vivo. Regression equations were generated for predicting the influence of plant parts on the IVDMD of each hybrid (Table 6). In all cases, the grain entered the model first, providing additional evidence that the proportion of grain in forage sorghum hybrids has the greatest influence on the subsequent IVDMD of forage sorghum silage. CONCLUSIONS
Forage sorghum silage IVDMD dynamics are most influenced by the proportion of grain in the silage. As grain increases silage IVDMD while sheath reduces silage IVDMD, it appears that to improve the IVDMD of forage sorghum silage one should select for increased grain yield rather than leaf yield. However, the sum of the IVDMDs of the ensiled plant parts did not equal the IVDMD of the silage. Further research is needed to determine the cause of the difference in IVDMD between silage and a blend of ensiled plant parts representing silage. It may not be possible to select superior forage sorghums for silage based on the IVDMD of a single plant part, perhaps due to plant part IVDMD interactions, or different effects of fermentation on separate plant parts compared to silage. REFERENCES Beadle, C.L., Stevenson, K.R., Newman, H.H., Thurtell, C.W. and King, K.M., 1973. Diffusive resistance, transpiration, and photosynthesis in single leaves of corn and sorghum in relation to leaf water potential. Can. J. Plant Sci., 53: 537.
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Cummins, D.G., 1981. Yield and quality changes with maturity of silage type sorghum fodder. Agron. J., 73: 988. Hart, S.P., 1987. Associative effects of sorghum silage and sorghum grain diets. J. Anita. Sci., 64:1779. Kirch, B., Hamma, S., Bolscn, K., Ilg, H. and Hoover, J., 1987. Whole plant forage and grain sorghum silages for growing cattle. Agric. Exp. Stn. Rcp. Prog. 514, Kansas State University, Manhattan, KS, p. 129. Kirch, B., Hamma, S., Bolscn, K., Riley, J. and Hoover, J., 1988. Whole plant forage and grain sorghum and corn silages for growing cattle. Agric. Exp. Stn. Rep. Prog. 539, Kansas State University, Manhattan, KS, p. 167. Marten, G.C., Goodrich, R.D., Schmid, A.R., Meiskc, J.C., Jordan, R.M. and Linn, J.G., 1975. Evaluation of laboratory methods for determining quality of corn and sorghum silages. II. Chemical methods for predicting in vivo digestibility. Agron. J., 67: 247. Nocek, J.E. and Russell, J.B., 1988. Protein and energy as an integrated system. Relationship of ruminal protein and carbohydrate availability to microbial synthesis and milk production. J. Dairy Sci., 71: 2070. Pedcrsen, J.F., Gorz, H.J., Haskins, F.A. and Ross, W.M., 1982. Variability for quality and agronomic traits in forage sorghum hybrids. Crop Sci., 22: 853. Rupp, R.A., Lane, G.T. and Leighton, R.F., 1975. Relative digestibility of two types of sorghums fed as silage. J. Dairy Sci., 58: 761. Sanchez-Diaz, M.F. and Kramer, P.J., 1971. Behavior of corn and sorghum under water stress and during recovery. Plant Physiol., 48:613. Schake, L.M., Ellis, W.C., Suarez, W.A. and Rigs, J.K., 1982. Preservation of sorghum plant portions harvested, processed, and ensiled at ten stages of maturity. Anita. Feed Sci. Technol., 7: 257. Statistical Analysis Systems, 1985. SAS User's Guide: Statistics. SAS Institute Inc., Cary, NC. Stout, D.G. and Simpson, G.M., 1978. Drought resistance of Sorghum bicolor 1. drought avoidance mechanisms related to leaf water status. Can. J. Plant Sci., 58:213. Thurman, R.L., Stalleup, O.T. and Reames, C.E., 1960. Quality factors of sorgo as a silage crop. Agric. Exp. Stn. Bull. 632, University of Arkansas, Fayetteville, AR. Thurman, R.L., Stallcup, O.T. and Siler, A.R., 1964. Leafage in sorgos for silage. Agric. Exp. Stn. Bull. 685, University of Arkansas, Fayetteville, AR. Tilley, J.M. and Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc., 18: 104. Vanderlip, R.L. and Reeves, H.E., 1972. Growth stages of sorghum (Sorghum bicolor (L.) Moench.). Agron. J., 64:13. Van Soest, P.J., 1982. Nutritional Ecology of the Ruminant. O and B Books, Corvallis, OR, 92 PP. Wanapat, M.R., Sundstol, F. and Hall, I.M.R., 1986. A comparison of alkali treatment methods used to improve the nutritive value of straw. II. In sacco and in vitro degradation relative to in vivo digestibility. Anita. Feed Sci. Technol., 14:215. White, J., Bolsen, K. and Kirch, B., 1988a. Relationship between agronomic and silage quality traits of forage sorghum cultivars. Agric. Exp. Stn. Rep. Prog. 539, Kansas State University, Manhattan, KS, p. 172. White, J., Bolsen, K., Kirch, B. and Pfaff, L., 1988b. Selecting forage sorghum cultivars for silage. Agric. Exp. Stn. Rep. Prog. 539, Kansas State University, Manhattan, KS, p. 177. Wilkinson, J.M. and Phipps, R.H., 1979. The development of plant components and their effects on the composition of fresh and ensilcd forage maize. 2. The effect of genotype, plant density, and date of harvest on the composition of maize silage. J. Agric. Sci., 92: 485.
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Forage sorghum silage dry matter disappearance as influenced by plant part proportion 1 J.S. White a, K.K. Bolsen b, G. Posleff and J.W. NeilP aAnimal Nutrition Inc., 6608 W. Main, Belleville, IL 62223, USA bDepartment of Animal Science and Industry, Kansas State University, Manhattan, KS 66506, USA CDepartment of Agronomy, Kansas State University, Manhattan, KS 66506, USA dDepartment of Statistics, Kansas State University, Manhattan, KS 66506, USA (Received 16 December 1989; accepted 15 October 1990)
ABSTRACT
White, J.S., Bolsen, K.K., Posler, G. and Neill, J.W., 1991. Forage sorghum silage dry matter disappearance as influenced by plant part proportion. Anim. Feed Sci. Technol., 33:313-322. Forage sorghum (Sorghum bicolor (L.) Moench) is widely grown for silage in the High Plains region of the U.S.A. The in vitro dry matter disappearance (IVDMD) dynamics of forage sorghum silage, as influenced by the proportion of ensiled plant parts, were examined. Five mid- to late-season forage hybrids were grown at Manhattan, Kansas, on a Smolan silty clay loam (fine, montmorillonitic, mesic Typic Agriustoll) in 1987. The hybrids were harvested at the hard dough stage of maturity. Grain yields ranged from 4.18 to 5.23 Mg ha -I, and silage yields from 13.72 to 16.45 Mg ha -~. At ensiling, five plants per hybrid were separated into grain, leaf, sheath and stalk parts, chopped, put into nylon bags and ensiled with their respective silages in pilot silos. The distribution of dry matter (g kg-~ ) among the plant parts was grain 282-413, leaf 208-229, sheath 107-170, stalk 195-401. The pH of each silage and plant part was determined at silo opening. The IVDMDs of plant parts were grain 769, leaf 577, sheath 527 and stalk 608 g kg -~, and ranged from 582 to 617 g kg -~ for silages. For each silage, each plant part was individuallyincreased to unity, then the IVDMD dynamics were plotted. The silages were reconstituted and the IVDMD determined. These ranged from 633 to 677 g kg-t. Statistically, the reconstituted silage IVDMD is the sum of the plant part IVDMD values, but the actual silage IVDMD was not. Regression equations were generated to predict silage IVDMD based on the proportion of plant parts for each hybrid. Grain had the greatest and a positive effect on silage IVDMD dynamics, whereas the sheath component had a negative effect.
INTRODUCTION
HistoricaUy, Kansas has been the leading state in forage sorghum (Sorghum bicolor (L.) Moench) silage production. Advantages of sorghum for silage compared to corn (Zea mays (L.) ) include: ( l ) lower production costs; (2) ~Journal contribution No. 89-220-J from the Kansas Agriculture Experiment Station, Manhattan, Kansas.
0377-8401/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
314
J.S. WHITE ET AL.
greater drought tolerance (Beadle et al., 1973; Stout and Simpson, 1978); ( 3 ) greater ability to recover from drought (Sanchez-Diaz and Kramer, 1971 ); (4) high yield potential under dryland conditions (Cummins, 1981 ); (5) higher crude protein content (Kirch et al., 1987, 1988; White et al., 1988a). Earlier studies have indicated that grain sorghum silage is nutritionally superior to forage sorghum silage. Rupp et al. (1975 ) compared the silage of grain and forage sorghum hybrids in a digestion trial and found that the grain sorghum silage had greater in vivo digestibility than did forage sorghum silage, and that the whole-seed disappearance was the same. The voluntary intake of silage by livestock is greater for grain sorghum silage than forage sorghum silage (Kirch et al., 1987, 1988; White et al., 1988a). Kansas trials have indicated that only high-grain-producing forage sorghum hybrids approach the feeding value of grain sorghum hybrids when they are fed as silage. While some high-yielding forage sorghum hybrids match grain sorghum hybrids in grain production, the forage to grain ratio is greater. White et al. (1988b) evaluated 80 forage sorghum cultivars and found that some non-grain-producing hybrids had the highest in vitro dry matter disappearance (IVDMD). Earlier work in Arkansas (Thurman et al., 1960) compared forage sorghum cultivars and noted that the male sterile hybrid RS 310 had the highest digestibility. Pederson et al. (1982) compared the quality and agronomic traits of 49 forage sorghum hybrids and suggested that the most rapid way to improve the quality of forage sorghum forage would be to improve IVDMD. In vitro dry matter disappearance is deemed an adequate measure of digestibility in that Marten et al. (1975), Wanapat et al. (1986) and earlier work in our laboratory (White et al., 1988a,b) have shown a high correlation between IVDMD and in vivo apparent dry matter (DM) digestibility. This experiment was conducted specifically to examine the influence of the grain fraction on the IVDMD of forage sorghum silage. It was hypothesized that the IVDMD of the silage would be the sum of the IVDMD of the ensiled plant parts. The objectives of this experiment were to: ( 1 ) monitor the dynamics of IVDMD as different ensiled plant parts were altered to comprise varying proportions of the silage DM; (2) develop regression equations to predict the silage IVDMD of forage sorghum hybrids based on plant part ratios; (3) determine which plant part (s) would be most useful as selection criteria when selecting for silage digestibility. MATERIALS AND METHODS
Five mid- to late-season forage sorghum hybrids were planted on 3 June 1987 and grown under dryland conditions (precipitation: 1 January-3 June, 328 ram, 3 June-15 October, 247 ram; data from weather library, Kansas State University, Manhattan, KS) on a Smolan silty clay loam soil (fine,
PLANTPARTPROPORTIONANDSORGHUMSILAGEDM DISAPPEARANCE
315
montmorillonitic, mesic, Typic Argiustoll) near the Kansas State University campus, Manhattan. The hybrids included were Cargill 455, DeKalb 25-E, Funk's 102F, Golden Acres-TE Silomaker and Northrup King 300 a. One month prior to planting, l 10 kg h a - ~of anhydrous ammonia were applied. A pre-plant soil test indicated that phosphorus and potassium were adequate. Carbofuran a ( 1.12 kg h a - i active ingredient (a.i.)) was applied in the furrow at planting and atrazine (2.25 kg ha-1 a.i.) was used as the pre-plant herbicide. Dimethoate (0.56 kg ha-~ a.i. ) was used to control greenbugs, spider mites and grasshoppers. A randomized complete block design with three replications was used, with each plot containing six rows 76 cm apart and 60 m in length. All plots were harvested at the hard dough stage (growth Stage 8 of Vandedip and Reeves, 1972). The stage of maturity was determined by visual and physical evaluation of several heads per plot. Silage yield was determined by harvesting three inside rows of each plot with a precision forage chopper. Grain yield was determined by clipping all heads from a random 18.3-cm section of the remaining inside row of each plot and threshing the heads in a stationary thresher. Three subsamples of five plants each were taken from the remaining inside row at harvest to determine plant part ratios. Plants were cut 5 cm above the soil surface, separated into grain, leaf blade (removed at the collar), sheath (removed at the node) and stalk parts. Separated materials were manually chopped to ~ 1 cm in length. Samples containing 100300 g of separate plants were then placed in nylon bags with a pore size of I mm. The nylon bags containing the plant part samples were ensiled along with their respective silages in plastic-lined, 210-1 pilot silos. Two pilot silos were used for each hybrid. The silos were stored at ambient temperature for 120-135 days prior to opening. At opening, the nylon bags were recovered for chemical analyses of samples. The pH was determined on the individual plant part samples and the surrounding silage. A sample of the plant material was diluted in ten times its weight of distilled water, mixed and allowed to equilibrate for 1.5 h prior to determining pH with an Orion Research Digital Ionalyzer 50 I. All pH samples were measured in duplicate. Samples were dried in a forced-air oven at 55 °C for 72 h and then ground in a Wiley mill to pass a l-mm screen. The IVDMD of each silage sample was determined in triplicate with a modified Tilley and Terry ( 1963 ) procedure. The modifications were the use of tared, oven-dry centrifuge tubes, deletion of the HgC1 solution and digesting samples in acid-pepsin for 40 h; 5% of each run were blanks to account aThe use of trade name products or identification of proprietary hybrids is for clarity in communication and to ensure the ability of other researchers to duplicate the study. It does not constitute an endorsement of those products and hybrids by the Kansas Agriculture Experiment Station, nor does it imply that similar products are not acceptable for a similar use.
316
J.S. WHITE ET AL.
for the microbial yield of the procedure. To determine IVDMD dynamics for sorghum hybrids having different proportions of plant parts, each silage and each plant part within a silage were combined in such a way that the samples had a specific plant part increased in 50-rag increments from the initial infield proportion (silage) to 1.0, in 50-mg increments. These samples were adjusted to weigh 500 mg ofDM + 10 mg and were digested in duplicate. The IVDMD of each silage and plant part of the respective hybrids was determined in triplicate. Using plant part ratio data, the silages of the hybrids were reconstituted using the ensiled plant parts. The reconstituted silage IVDMD was determined in triplicate. The summation IVDMD of a hybrid was calculated by multiplying the proportion of the DM per part by the IVDMD of the respective part, and then adding the four values. Data were statistically analyzed with analysis of variance procedures using the General Linear Model of the Statistical Analysis Systems (S.A.S.) (S.A.S., 1985). The regression equations were generated by S.A.S. (1985) using the stepwise procedure. DISCUSSION
Agronomic data for the five forage sorghum hybrids are shown in Table 1. The hybrids reached half-bloom 71-77 days after planting and were harvested 108-118 days after planting (data not shown). The hybrid Silomaker had the lowest grain yield and NK 300 had the lowest silage yield. There were no significant differences among the hybrids for proportion of DM as leaf or sheath. The hybrid DeKalb 25-E had the highest proportion of stalks and the highest forage to grain ratio. The plant subsamples taken for determining plant part proportions agreed well, i.e. within 5 percentage units, with the harvest data for four out of the five hybrids. It appears that the use of subsamples to TABLE 1 Dry m a t t e r yields ( M g h - ~) a n d plant parts ( g kg - t D M ) for five forage s o r g h u m h y b r i d s Hybrid
D M yield
Plant part
Grain
Silage
Grain
Leaf
Sheath
Stalk
Cargill 455 D e K a l b 25-E F u n k ' s 102F G A - T E Silomaker N K 300
5. I a 4.9 a 5.2 ~ 4.2 5.0 a
15.7 *'c 16.4 a'¢ 14.7 a'b 14.2 b 13.7
372 a'b 282 a 374 ~'b 399 ~'b 413 b
208 210 210 215 229
124 107 127 133 170
295 bx 401 d 289 b'c 253 Lb'c 195 a'b
SE
0.17
0.40
44.2
17.8
M e a n s in a c o l u m n w i t h o u t the s a m e superscript differ significantly ( P < 0.05).
19.9
23.0
PLANT PART PROPORTION AND SORGHUM SILAGE DM DISAPPEARANCE
317
determine grain proportion may overestimate the proportion of grain in the crop. All silages and plant parts were well preserved, as indicated by the terminal pH values (Table 2) and no observed spoilage or off odors. The pH values of the grain were the highest. Schake et al. ( 1982 ) ensiled sorghum plant parts and reported that volatile fatty acid production during the fermentation process was much lower for the head plant part than for leaf or stalk parts. The pH values of the plant parts are taken as evidence that the bagged plant parts did undergo a fermentation and were successfully ensiled. There were significant differences among hybrids for IVDMD of all parts (Table 3). For all hybrids, the grain component had the greatest IVDMD, whereas the sheath had the lowest. Thurman et al. (1960) reported that the leaf of Atlas forage sorghum had the highest digestibility and suggested that TABLE2 Silage a n d plant part p H values for five forage s o r g h u m h y b r i d s Hybrid
Silage
Plant part Grain
Leaf
Sheath
Stalk
Cargill 455 D e K a l b 25-E F u n k ' s 102F G A - T E Silomaker N K 300
4.06 c 3.88 ~ 4.07 c 3.98 b 4.06 c
4.32 a'b 4.42 a 4.36 a'b'~ 4.41 b'c 4.68 d
4.18 ¢ 4.04 a 4.22 d 4.28 ~ 4. l0 b
4.02 b 3.97" 4.26 d 4.16 c 4.06 b
4.10 b 3.80" 4.16 c 4.14 b'c 4.24 d
SE
0.011
0.017
0.010
0.012
0.013
M e a n s in a c o l u m n w i t h o u t t h e s a m e superscript differ significantly ( P < 0.05 ).
TABLE 3 Plant part I V D M D (g k g - i ) for five forage s o r g h u m h y b r i d s Hybrid
P l a n t part Grain
Leaf
Sheath
Stalk
Cargill 455 D e K a l b 25-E F u n k ' s 102F GA-TE Silomaker N K 300
724 "w 775 b,w 782 b,w 773 b,w 792 b'w
566 a'y 614 c'x 565 a'b,y 601 b.c,y 540 a'y
490 a,z 542 b.y 532 a,y 572c.z 496 a'z
608 b'x 604 b'x 552 ~'y 653c.~ 622 b'x
Mean SE
769 10.3
577 10.3
527 10.3
608 10.3
a'b'CMeans in a c o l u m n w i t h o u t the s a m e superscript differ significantly ( P < 0.05). w'~'Y'ZMeans in a row w i t h o u t the s a m e superscript differ significantly ( P < 0.05).
J.S. WHITE ET AL.
318
forage sorghum silage quality could be improved by the development of leafy hybrids (Thurman et al., 1964). Our data suggest that increasing the grain proportion of forage sorghum would improve silage digestibility to a greater extent than increasing the leaf proportion in improved forage sorghum hybrids. Increasing the proportion of a plant part in silage samples gave an IVDMD response (shown in Figs. 1-4). For all silagcs, plotting IVDMD against increasing proportions of grain produced a positive response (Fig. 1 ), whereas plotting IVDMD against the proportion of sheath gave a negative response (Fig. 2). Plots of IVDMD against proportion of leaf (Fig. 3 ) and stalk (Fig. 4 ) produced less variation than did plots of IVDMD against grain or sheath. Silage chemical composition differed (Table 4). The hybrids had similar
. . . . ..... - ---
800 -
....
25 E 102 F 455 - SILOMAKER
J"
NK,~o
..-"
700
--"
. ~. ~':-~"
. --.5~
,'~~ ./:'.." ...... ... /.:,.-"
600
500 I 100
I 200
I 300
I 400
[ 500
I 600
I 700
I 800
I 900
I 1000
g grain kg-1 sample
Fig. 1. Effect on IVDMD of increasing the proportion of grain in the silage samples.
800
"
. . . . .... .... . . . .
25 E 102F 455 SILOMAKER NK300
c•70O 2_ ol
a
:E 600
......
~ - - - f -" "_ - . ~ - ~ " -
S00 I 100
I 200
I 300
I 400
I S00
I S00
I 700
I 800
i 900
I 1000
g l e a f k g - 1 sample
Fig. 2. Effect on IVDMD of increasing the proportion of leaf in the silage samples.
PLANT PART PROPORTION AND SORGHUM SILAGE DM DISAPPEARANCE
800 -
319
25 E 102 F 455 SILOMAKER NK300
. . . . ..... .... . . . .
5700 oi
c~ :E
~ 60o S00 I
I
I
I
I
I
I
I
I
I
100 20o 3oo 4oo 5oo 6oo 7oo 800 90o lOOO g sheath kg-1 sample
Fig. 3. Effect on IVDMD of increasing the proportion of sheath in the silage samples.
800
L .... ..... .... . . . .
25 E 102 F 455 $1LOMAKER NK300
57oo
L :E
._.
L
:__. _. --- -_-.-_----
;--..
500
I 100
20l) 31~0 440 soo ' s~o 7~0 s~o 90o ' 10100 g stalk kg-1 sample
Fig. 4. Effect on IVDMD of increasing the proportion of stalk in the silage samples.
crude protein and ash contents. Significant differences were observed for neutral detergent fiber (NDF), ether extract, acid detergent fiber (ADF) and permanganate lignin. Non-structural carbohydrates (NSC) were calculated after Noeek and Russell ( 1988 ). Higher NSC values did not consistently give higher IVDMD. Wilkinson and Phipps (1979) found only small differences among silage in vitro digestibilities of three similar corn varieties. Likewise, we observed small differences among the silage IVDMD, but significant differences among plant part IVDMD. Cummins (1981 ) compared four forage sorghum hybrids and showed greater IVDMD for the stalk than for the leaf plant part. These data indicate that the IVDMD of the forage sorghum silage is not the
J.S. WHITE ET AL.
320 TABLE 4 Silage chemical composition (g kg- t DM) of the five forage sorghum hybrids Hybrid
Crude protein
NDF
Ether extract
Ash
NSC*
ADF
Lignin
Cargill 455 DeKalb 25-E Funk's 102F GA-TE Silomaker NK 300
78 73 74 73 77
558 d 531 c 496 a'b 518 b'c 476"
30 b 24 a 27 a'b 32 b 31 b
67 63 61 61 69
307 a 349 b 379 c'd 353 b'c 388"
347 ~'b 366 b 339 ~'b 320" 333"
45 a'b 57 ~ 45 ~'b 40" 52 b'c
Mean SE
75.0 5.0
515.8 12.2
28.8 2.5
64.2 4.0
355 12.6
341.0 9.8
47.8 6.3
Means in a column without the same superscript differ significantly ( P < 0.05).
TABLE 5 Disappearance of silage, reconstituted silage, and sum of plant parts for five forage sorghum hybrids (gkg -~ ) Hybrid
IVDMD
Cargill 455 DeKaib 25-E Funk's 102F GA-TE Silomaker NK 300 SE
Silage
Reconstituted silage
Sum of parts
584 b'y 582 b'y 588 b'y 615 a'y 617 a'y
633 b,z 664 a,~ 634 b,~ 677 ~'z 639 b'~
628 a,z 648 b.... 638 ~'a'z 679 a'~ 656 b'~
2.38
6.62
5.10
a,bMeans in a column without the same superscript differ significantly ( P < 0.05 ). Y'ZMeans in a row without the same superscript differ significantly ( P < 0.05).
TABLE 6 Regression equations for predicting silage IVDMD for five forage sorghum hybrids Hybrid
Cargill455 DeKalb 25-E Funk's 102F GA-TE Silomaker NK 300
Intercept
549 552 509 532 508
Slope Grain
Leaf
Sheath
Stalk
145 191 272 201 304
24 37 -
-78 -40 -19
16 2 11 93
SE
R2
4.9 10.3 7.7 14.0 10.4
0.97 0.89 0.95 0.77 0.95
PLANTPARTPROPORTIONANDSORGHUMSILAGEDM DISAPPEARANCE
321
sum of the plant part IVDMDs. However, given the large variation in plant part proportion between plants, within plots and between plots, there is great potential for sampling error. Van Soest (1982) suggested another potential reason for the observed non-additivity: "Rumen bacteria are partially digestible and the comparability of in vivo to in vitro digestibility value rests on the fact that ruminant feces are composed of roughly equivalent amounts of undigested cell wall and bacteria remnants similar to those obtained in the in vitro situation". Van Soest also indicates that the difference between apparent and true digestibility in vitro is on the order of 11.5 units of digestibility, whereas in vivo the difference is 13.9 units of digestibility. In our study, the reconstituted silage IVDMD was statistically equivalent to the sum of the plant part IVDMDs (Table 5 ). There seemed to be some associative effect, i.e. a non-linear IVDMD response, when plant parts were blended to reconstitute a silage. The proportion of grain in the ideal forage sorghum hybrid for silage is limited by such associative effects. Hart (1987) demonstrated that 15-30% grain in a sorghum grain and silage-based diet improved the digestibility and dry matter intake of cattle, but higher proportions of grain (45-60%) did not result in further increases in vivo. Regression equations were generated for predicting the influence of plant parts on the IVDMD of each hybrid (Table 6). In all cases, the grain entered the model first, providing additional evidence that the proportion of grain in forage sorghum hybrids has the greatest influence on the subsequent IVDMD of forage sorghum silage. CONCLUSIONS
Forage sorghum silage IVDMD dynamics are most influenced by the proportion of grain in the silage. As grain increases silage IVDMD while sheath reduces silage IVDMD, it appears that to improve the IVDMD of forage sorghum silage one should select for increased grain yield rather than leaf yield. However, the sum of the IVDMDs of the ensiled plant parts did not equal the IVDMD of the silage. Further research is needed to determine the cause of the difference in IVDMD between silage and a blend of ensiled plant parts representing silage. It may not be possible to select superior forage sorghums for silage based on the IVDMD of a single plant part, perhaps due to plant part IVDMD interactions, or different effects of fermentation on separate plant parts compared to silage. REFERENCES Beadle, C.L., Stevenson, K.R., Newman, H.H., Thurtell, C.W. and King, K.M., 1973. Diffusive resistance, transpiration, and photosynthesis in single leaves of corn and sorghum in relation to leaf water potential. Can. J. Plant Sci., 53: 537.
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Cummins, D.G., 1981. Yield and quality changes with maturity of silage type sorghum fodder. Agron. J., 73: 988. Hart, S.P., 1987. Associative effects of sorghum silage and sorghum grain diets. J. Anita. Sci., 64:1779. Kirch, B., Hamma, S., Bolscn, K., Ilg, H. and Hoover, J., 1987. Whole plant forage and grain sorghum silages for growing cattle. Agric. Exp. Stn. Rcp. Prog. 514, Kansas State University, Manhattan, KS, p. 129. Kirch, B., Hamma, S., Bolscn, K., Riley, J. and Hoover, J., 1988. Whole plant forage and grain sorghum and corn silages for growing cattle. Agric. Exp. Stn. Rep. Prog. 539, Kansas State University, Manhattan, KS, p. 167. Marten, G.C., Goodrich, R.D., Schmid, A.R., Meiskc, J.C., Jordan, R.M. and Linn, J.G., 1975. Evaluation of laboratory methods for determining quality of corn and sorghum silages. II. Chemical methods for predicting in vivo digestibility. Agron. J., 67: 247. Nocek, J.E. and Russell, J.B., 1988. Protein and energy as an integrated system. Relationship of ruminal protein and carbohydrate availability to microbial synthesis and milk production. J. Dairy Sci., 71: 2070. Pedcrsen, J.F., Gorz, H.J., Haskins, F.A. and Ross, W.M., 1982. Variability for quality and agronomic traits in forage sorghum hybrids. Crop Sci., 22: 853. Rupp, R.A., Lane, G.T. and Leighton, R.F., 1975. Relative digestibility of two types of sorghums fed as silage. J. Dairy Sci., 58: 761. Sanchez-Diaz, M.F. and Kramer, P.J., 1971. Behavior of corn and sorghum under water stress and during recovery. Plant Physiol., 48:613. Schake, L.M., Ellis, W.C., Suarez, W.A. and Rigs, J.K., 1982. Preservation of sorghum plant portions harvested, processed, and ensiled at ten stages of maturity. Anita. Feed Sci. Technol., 7: 257. Statistical Analysis Systems, 1985. SAS User's Guide: Statistics. SAS Institute Inc., Cary, NC. Stout, D.G. and Simpson, G.M., 1978. Drought resistance of Sorghum bicolor 1. drought avoidance mechanisms related to leaf water status. Can. J. Plant Sci., 58:213. Thurman, R.L., Stalleup, O.T. and Reames, C.E., 1960. Quality factors of sorgo as a silage crop. Agric. Exp. Stn. Bull. 632, University of Arkansas, Fayetteville, AR. Thurman, R.L., Stallcup, O.T. and Siler, A.R., 1964. Leafage in sorgos for silage. Agric. Exp. Stn. Bull. 685, University of Arkansas, Fayetteville, AR. Tilley, J.M. and Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc., 18: 104. Vanderlip, R.L. and Reeves, H.E., 1972. Growth stages of sorghum (Sorghum bicolor (L.) Moench.). Agron. J., 64:13. Van Soest, P.J., 1982. Nutritional Ecology of the Ruminant. O and B Books, Corvallis, OR, 92 PP. Wanapat, M.R., Sundstol, F. and Hall, I.M.R., 1986. A comparison of alkali treatment methods used to improve the nutritive value of straw. II. In sacco and in vitro degradation relative to in vivo digestibility. Anita. Feed Sci. Technol., 14:215. White, J., Bolsen, K. and Kirch, B., 1988a. Relationship between agronomic and silage quality traits of forage sorghum cultivars. Agric. Exp. Stn. Rep. Prog. 539, Kansas State University, Manhattan, KS, p. 172. White, J., Bolsen, K., Kirch, B. and Pfaff, L., 1988b. Selecting forage sorghum cultivars for silage. Agric. Exp. Stn. Rep. Prog. 539, Kansas State University, Manhattan, KS, p. 177. Wilkinson, J.M. and Phipps, R.H., 1979. The development of plant components and their effects on the composition of fresh and ensilcd forage maize. 2. The effect of genotype, plant density, and date of harvest on the composition of maize silage. J. Agric. Sci., 92: 485.