Nutritive value and ensiling characteristics of maize herbage as influenced by agronomic factors

;l~tim/ FeedScienceand Technology. 38 (1992) Elsevier Science Publishers B.V.. Amsterdam

I l-24

11

Nutritive value and ensiling characteristics of maize herbage as influenced by agronomic factors J.R. Russell”, N.A. Irlbeck”, A.R. Ha:lauerb and D.R. Buxtonc “Departtnent ofAnimal Scimce, Iowa State C’niversity. Ames, IA. USA bDepnrttnent ofAgronomy, lowa Slare Universily, Ames, IA. USA ‘Fteld Crops Research Unit, US Dairy Forage Research Cluster. AgriculteralRerearch DepartmW ofAgrrc!dture. Antes. IA 50011. USA

(Received

I November

Service. US

1990; accepted 15 January 1992)

ABSTRACT Russell, J.R., Irlbeck, N.A. Hallauer, A.R. and Buxlon, D.R., 1992. Nutritive value and ensilingcharact&tics of maize herbageas influenced by agronomic factors. Anim. FeedSci. Techrzoi., 38: 24.

II-

An experiment was conducted to investigate cffccts of genotype, hybrid generation (F, vs. F2), plant density and harvest date on the composition and ensiling characteristics of maize (Zea mow L.) herbage. In Year I, three maize hybrids (A632xLH38. early maturing, B73XMol7, mediummaturing and B73xPa91, late-maturing) were evaluated in three replications at plant densities of 4.9. 6.9 and 8.9 plants m? and harvested 0, 14 and 28 days after physiological maturity. In Year 2, F,- and Frgenerations of the hybrids used in Year in Year and harvested at physiological maturity. At harvest, samples were taken for determination of herbage and grain yields, grainto-stwer ratio and for analysis as either freshly harvested herbage or silage prepared in polyethylene bags. Herbage yields at physiological maturity were lower (Px 0.01) from the early-maturing hybrid than other hybrids, from the F,.- than F,-generation of the hybrids, and from maize grown at 4.9 plants m-’ than at higher plant densities. Maize herbage yields were also lower (Px0.01 ) later harveu dates. Both grain-to-stover ratios and in vitro digestible dry matter (IVDDM) concentrations of the for-

I were grown as

I

at

ages were greater (PcO.05) from the early-maturing hybrid than from other hybrids and less (P-zO.05 lfrom the F,-veneration maize than F,-veneration maize. Later harvest increased (P
I)

Correspondence IA 50011, USA.

to: J.R. Russell, Department

0 1992 Elsevier Science

of Animal

Science, Iowa State University.

Publishers B.V. All rights reserved 0377-8401/92/$05.00

Ames.

I2

J.R. RUSSELL ET AL.

R&&s imply that agronomic factors that changegrain-to-stover ratio do not greatly influence maize digestibilityorensilingcharacteristics. Therefore, factorsoptimizingyieldsandeconomic returns should be emphasized when growing maize for silage.

INTRODUCTION

The proportion of grain or ear in the dry matter (DM) of maize (Zeu muys L.) herbages may be influenced by many factors, including genotype (Hemken et al., 1971; Phipps and Weller, 1979; Fisher and Fairey, 1982), plant density (Cummins and Dobson, 1973; McAllan and Phipps, 1977; DeLoughery and Crookston, 1979; Phipps and Weller, 1979) and harvest date (McAllan and Phipps, 1977; Wilkinson et al., 1978; Phipps and Weller, 1979; Russell, 1986). Agronomic management systems recommended for producing maize herbage for silage have emphasized practices that maximize the proportion of grain in the plant DM ( Andrieu and Demarquilly, 1974; Phipps et al., 1979; Fisher and Fairey, 1982). The basis of this recommendation is the greater quantity of starch and, therefore, digestible DM in maize grain than in maize stover ( Andrieu and Demarquilly, 1974). Nonstructural carbohydrate concentration in maize stover, howe&, is inversely related to the proportion of grain in maize herbage (Bunting. 1976; McAllan and Phipps, 1977; Phipps and Weller, 1979; R&eh, 1986)ITherefore, digestibility of freshly harvested maize herbage has not been influenced by proportion of grain in the forage (Bunting, 1976; McAllan and Phipps, 1977; Phipps and Weller, 1979). Because most non-structural carbohydrates in maize stover are water soluble, a large proportion of non-structural carbohydrates in maize herbage containing a low proportion of grain is metabolized during silage fermentation (McAllan and Phipps, 1977; Phipps and Weller, 1979). Losses of water-soluble carbohydrates during silage fermentation and their effects on silage nutritive value are inconsistent. Maize silages produced from plants containing a low proportion of grain have contained greater concentrations of acid detergent fiber (ADF) and acid detergent lignin (ADL), and lesser concentrations of digestible organic matter (McAllan and Phipps, 1977), causing less milk production when given to dairy cows (Phipps et al., 1979; Fisher and Fairey, 1982). Other studies have found little effect of the proportion of grain in maize herbage on composition and digestibility of maize silage (Hemken et al.. 1971: Wilkinson and Phinas. 1979). or on the milk production of cows fed on this silage (Hemken et.& l97i ). The effects of grain proportion on maize nutritive value and ensiling characteristics need to be further evaluated to develop management systems that either reduce economic inputs or maximize yields without adversely influencing silage nutritive value. Economic inputs of purchasing maize seed may be reduced by planting the

MAC&

HERBAGE:

N”TR,T,YE

VALUE AND ENSlLlNO

PROPERTIES

13

seed of the Fz-generation of maize hybrids for production of herbage. The FT generation has lower grain yields than the Fr-generation of specific hybrids (Lopez-Perez, 1977). The effects of hybrid generation on the nutritive value and ensiling characteristics of maize herbage, however, have not been studied. The objective of these experiments was to evaluate the effects of altering the grain-to-stover ratio by use of different genotypes and generations of maize hybrid, plant densities and harvest dates on the nutritive value and ensiling characteristics of maize forage. MATERIALS AND METHODS

Maize hybrids were planted in replicated plots at a site having primarily Clarion (tine-loamy, mixed, mesic Typic Hapludolls) and Webster (tineloamy mixed, mesic Typic Haplaquolls) soils near .4mes, IA, for 2 years. Fertilization for each year consisted of 40.8 ka ha-’ of P and K aodied in the preceding fall and 9 1.6 kg ha-’ of N in the form of urea applied in the spring. Precipitation over the growing season was 466 mm and 593 mm in Years 1 and 2, respectively, these values being 26 mm and 166 mm above the IO-year average for the site. Average temperatures were 20.2”C and 21.6% in Years 1 and 2, respectively, which are 0.4”C below and 0.9”C above the lo-year average for the site. Year 1

Three maize hybrids, A632 x LH38 (early-maturing), B73 x Mo17 (medium-maturing) and B73 x Pa9 I (late-maturing), were planted on 23 April in nine 5.5 mx 5.5 m plots, distributed in three replications in a randomized complete-block design. After emergence, plots were thinned to plant densities of 4.9, 6.9 and 8.9 plants m-* in each replication. Silking of the early-, medium- and late-maturing hybrids occurred 83,89 and 92 days after planting and was not influenced by density. Two samples of ten maize plants were harvested from each plot at physiological maturity of the plants, determined as 50 days post-silking, and 14 and 28 days after physiological maturity. One sample of the freshly harvested herbage was weighed, coarsely chopped through a wood chipper and more finely chopped to a particle length of approximately 6.4 mm with a salad chopper. Silages were prepared by placing I kg of chopped herbage in 25.4 cmx 50.8 cm polyethylene bags. The bags were evacuated, sealed and incubated at 37°C for 60 days. To determine the grain-to-stover ratio, ears were removed from the remaining ten-plant sample, and the grain was shelled and weighed. Cobs and husks were returned to the leaves and stalks, and the resulting stover was weighed. Three weeks after physiological maturity, grain was harvested from two rows

14

IX. R”SSELl. HAL.

of plants in each plot, and yield was determined. Herbage yields were calculated from grain-to-stover ratios at each harvest date, and grain yields were determined 3 weeks after physiological maturity.

Year 2 The F,- and Fs-generations of the same hybrids used in Year 1 were planted on 26 April in nine 1.5 m x 5.3 m plots distributed randomly in three rephcations. After emergence, plots were thinned as in Year 1. Silking occurred at 86, 89 days; 92, 95 days: and 94, 95 days post-planting in the F,- and F2generations of the early-, medium- and late-maturing hybrids. Two samples of 50 plants were harvested from each plot at physiological maturity, as determined by the loss of the ‘milkline’ (Crookston and Afuakwa, 1983), and the development of the ‘black layer’ in the translocation zone of the kernels. The Ft- and Fz-generations of the early- and mediummaturing hybrids were harvested at 137,137 and 143,144 days post-planting. Because a killing frost occurred, all plots of the F,-generation and six plots of the F,-generation of the late-maturing hybrid were harvested 15 1 days postplanting, which was before physiological maturity according to the measurements used. Maize herbage was coarsely chopped with a wood chipper and more finely ground through a 1.3-cm screen. Silages from the ground forages were prepared as in Year I. Ears were removed from the remaining sample, and the grain-to-stover ratios were determined as in Year 1. Grain yield was determined 4 weeks after physiological maturity. Herbage yields were calculated from grain-to-stover ratios determined at physiological maturity, and grain yields were determined 4 weeks after physiological maturity.

Chemical analyses Dry-matter concentration of the silages was determined by toluene distillation (Association of Offtcial Analytical Chemists, 1980). Dry-matter concentrations of freshly harvested herbage, stover and grain were determined and subsamples of the silages prepared for analysis by drying at 60°C for 48 h. Dried samples were ground through a l-mm screen and analyzed for neutral detergent fiber (NDF; Van Soest and Robertson, 1980), ADF, ADL, (Goering and Van Soest, 1970)) total non-structural carbohydrates (TNC; Smith, 198 1) and in vitro digestible DM (IVDDM) by the method of Tilley and Terry ( 1963) as modified by Marten and Barnes ( 1980). Subsamples of silages were prepared for analysis of N by freeze-grinding (Danley and Vetter, 197 1) _Nitrogen was determined in dried freshly harvested herbage and freezeground silage by the Kjeldahl procedure (Association of Offtcial Analytical

MAlZE

HERBAGE:

N”TRrrI”E”AL”E

AND ENSlLlNC

PROPElmES

IS

Chemists, 1980 ), except that a copper catalyst (Kjeltabs, Tecator, Verndon, VA) was used during digestion. Total and individual volatile fatty acids (VFA) and lactic acid were determined on water extracts. Total VFA were determined by steam distillation ( Kromman et al., I967 ) . In Year 1,individual WA were determined by gasliquid chromatography (Supelco, 1975) ’ and lactic acid by the calorimetric method of Barker and Summerson ( 1941). In Year 2, samples were butylated, and individual VFA and lactic acid were quantified by gas-liquid chromatography (Salanitro and Muirhead, 1975). Statistical

analyses

Analyses of variance of the data were conducted using the General Linear Models procedure of the Statistical Analysis System (Barr et zL, 1979).The concentrations of DM, IVDDM, NDF, ADF, ADL, TNC and CP were analyzed as split-plot models with main effects of year, genotype, plant density and preservation method (unensiled or ensiled) for herbages from the F,hybrid harvested at physiological maturity in both years; genotype, plant density, harvest date and preservation method for herbages produced from the three harvest dates in Year 1; and genotype, generation of hybrid, plant density and preservation method for herbages from both generations harvested in Year 2. Because no interactions between preservation method and the other treatments were observed, DM, IVDDM, NDF, ADF, ADL, TNC and CP are reported as the combined means of the herbages and silages. The grain-tostover ratios, VFA and lactic acid concentrations of the silages were analyzed by split-plot models similar to those just described, except that preservation method was not a factor. Herbage and grain yields were analyzed as split-plot models with main effects of year, genotype and plant density for the F, hybrid in both years and genotype, generation of hybrid and plant density in Year 2. To quantify the effect of composition of the herbages and silages on their IVDDM concentrations, stepwise regressions were calculated by a forward selection procedure (Barr et al., 1979) using the grain-to-stover ratio and the concentrations of DM, NDF, ADF, ADL, TNC and CP as independent variables. To quantify the effect of composition of the freshly harvested herbages on the lactic acid concentrations of their respective silages, stepwise regressions were calculated by a forward selection process using the grain-to-stover ratio and the concentrations of DM, IVDDM, NDF, ADF, ADL, TNC and CP of the freshly harvested herbages as independent variables. ‘Mentionof a trade name or proprietaryproduct does not constitute a guarantee or warranty of the product by Iowa State University or USDA, nor imply its approval to the exclusion of other products that may be suitable.

16 RESULTS

AND

DISCUSSION

Hybrid andplant densityeffects Over the 2 years of the experiment, mean herbage and grain yields increased (PC 0.0 I), and grain-to-stover ratios decreased (PC 0.0 1) , as the relative maturity rating of the maize hybrids increased (Table I ). Maize grown at 4.9 plants m-* had lower (PcO.01) herbage yields than when grown at greater plant densities. Plant density, however, had no significant effects or interactions with maize hybrid on grain yields or grain-to-stover ratios. Mean DM (PcO.01) and IVDDM (P=O.O4) concentrations of the herbage and silage, like the grain-to-stover ratio, were higher for early-maturing maize than for either of the other hybrids (Table 2). However, the concentrations of NDF (ILO.01) and ADF (P=O.O3) were higher and that of CP lower (P=O.Ol) in the medium-maturing hybrid than either the early- or latematuring hybrid. TABLE

I

Effect of maize hybrid and plant density on the total and grain yields and grain-to-stover ratios of herbage. Values are means of three replications of the F,-generation of each hybrid in 2 years. In this and following tables, early-, medium- and late-maturing hybrids are A632xLH36, B73xMol7 and B73xPaVl Relative maturity of hybrid

Plant density (plants m-‘)

Herbage yield1 (kgDMha-‘)

Early

4.9 6.9 a.9

9818 12270 10363

5136 5978 5318

1.10 0.98 1.13

Medium

4.9 6.9 8.9

12991 14945 14748

6628 6721 6469

1.03 0.86 0.83

Late

4.9 6.9 8.9

14354 16282 19034

6843 7722 8800

0.91 0.90 0.85

~

Grain yield2 (kgDMha-‘)

SEM

788.9

411.4

Significance Hybrid (h) Plant density (d) hxd

co.01 10.01 0.08

co.01 0.13 0.11

‘Values calculated by using the grain yields and the grain-to-stow ratios. ‘Measured 3 and 4 weeks after physiological maturity in Years I and 2. ‘Measured at physiological maturity. SEM, standard error of the mean.

Grain-to-stow

0.06

cO.OI 0.13 0.25

I

ratio’

MAlZE

HERBAGE:

N”TR,T,“E”AL”E

AND ENSILING

PROPERTIES

17

TABLE 2 Effect of maize hybrid and plant density on the composition Values we means of three replications of the F,-generalion herbagc at physiological Relative maturity of hybrid

of freshly harvested and ensiled herbage. of freshly harvested and ensiled maize

maturily Plant density (plantsm-“)

DM (gkg-‘1

Proportion

of DM (g kg-‘)

IVDDM

NDF

ADF

AD1

TNC

CP

Early

4.9 6.9 8.9

467 457 430

750 748 761

455 455 457

236 241 234

36 37 35

340 367 346

69 70 74

Medium

4.9 6.9 8.9

381 388 373

750 721 739

459 503 466

237 274 245

36 45 38

358 314 332

66 64 61

Late

4.9 6.9 8.9

407 377 400

736 735 720

431 452 465

227 245 252

36 38 38

356 376 331

71 73 66

SEM

Significance Hybrid(h) Plant density hxd

(d)

14.5

9.7

9.8

co.01 0.35 0.40

0.04 0.40 0.32

0.01 0.04 0.09

6.3

1.9

0.03
0.09 0.04 0.20

14.5

0.22 0.37 0.12

2.1

co.01 0.45 0. I2

DM, dry matter; IVDDM, in vitro digestible dry matter; NDF, neutral detergent fiber; ADF, acid detergent titer, ADL, acid detergent lignin; TNC, total nonstructural carbohydrates; CP, crude protein.

Although plant density did not significantly affect grain-to-stover ratios, maize forages grown at a density of 6.9 plants m-2 had higher concentrations of NDF (P=O.O4), ADF (P-=0.01 ) and ADL (P=O.O4) than maize grown at densities of either 4.9 or 8.9 plants m-‘. The increase in mean ADF concentration at the intermediate plant density primarily resulted from the effect of plant density on the medium-maturing hybrid (hybrid x density, PK 0.04). Concentrations of lactic (P=O.O2) and acetic (P=O.O4) acids of silages produced from the early-maturing hybrid were lower than those made from the medium- or late-maturing hybrid (Table 3). Plant density had no effect on the concentrations of lactic, acetic or butyric acids. Harvest date effects In Year 1, harvest 14 and 28 days after physiological maturity resulted in a lower (P-C0.01) herbage yield, higher (PC 0.0 1) grain-to-stover ratio, higher concentrationsofDM (P
J.R. RUSSELLET AL.

18 TABLE 3

Effect of maize hybrid and plantdensity on concentration of lactic, acetic and butyric acids in silage. Values are means of three replications of the F,.generation of ensiled maize herbage harvested at physiological manwily

kg-‘)

Relative maturity of hybrid

Plant density (plantsm-*)

Proportion of DM (g Lactic acid

Acetic acid

Butyric acid

Early

4.9 6.9 8.9

31

11.3 12.7 13.1

0.37 0.23 0.25

4.9 6.9 8.9

50 50 46

14.1 14.3

IS.0

0.33 0.00 0.00

4.9

50 47 42

14.5 II.8 15.0

0.00 0.72 0.00

Medium

Late

6.9 8.9

Significance Hybrid (h ) Plant density(d) hxd

38 44

3.4

0.97

0.296

0.02 0.89 0.31

0.04 0.22 0.34

0.76 0.66 0.45

lower concentrations of ADF (PcO.01) and TNC (P=O.O2) in the herbages and silages than harvest at physiological maturity (Table 4). Later harvest also resulted in iower concentrations of lactic (P< 0.0 I ) and acetic (P=O.O I ) acid in the silages. Harvest date also had interactions with hybrids for herbage yield (P=O.O2) and the concentrations of DM (P=O.O4), IVDDM (P-eO.01) and acetic acid (P< 0.0 1) . Herbage yields of the early-, medium- and late-maturing hybrids decreased by 6.9,8. I and 20.2% during the 4 weeks after physiological maturity. Reductions in DM concentration of the forages and silages over the 28day sampling period were greater for medium-maturing hybrid (204 g DM kg-‘) than for either early-maturing ( 145 g DM kg-‘) or late-maturing ( 146 g DM kg-‘) hybrid. The IVDDM concentrations in silages decreased from physiological maturity to 1Cday post-physiological maturity and increased thereafter for the early- and medium-maturing hybrids. In contrast, concentrations of IVDDM and acetic acid increased from physiological maturity to 14-day post-physiological maturity and decreased thereafter for the late-maturing hybrid.

Year I: effect of hawesi date on the yield and wmposition of freshly harvested and en&d maize herbage. Values are the means of three replications of three hybrids grown at three plant densities. DM. IVDDM, NDF, ADF, ADL, TNC and CP values are the combined means of freshly harvested and ensiled herbages. Lactic, acetic and butyric acid values are the values for ensiled herbages Item

Harvest

date (days

50 Herbage

yield

Grain-to-stover

(he ha-‘)

post-silking)

0.97

937 I 1.10

DM(gkg-‘) Proportion IVDDM NDF ADF ADL TNC CP

Significance

492.9

co.01

78

64

10688

ratio

SEM

1.26

0.107


514

22.3

co.01

731 425 247 37 327 76

14.4 14.6 11.7 2.7 14.0 4.6

0.16 0.14 co.01 co.01 0.02 0.02

of DM (g kg-‘)

Lactic acid Acetic acid Butyric acid

721 439 268 32 343 69 49 16 0.2

719 433 257 37 326 70 33 I3 0.1

24 I2 0.0

4.1 2.6 0.29


Hybrid generation effects In Year 2, the F2-generation of main hybrids had lower (PcO.01) herbage yields, grain yields and grain-to-stover ratios than the F,-generation (Table 5 ). Herbages and silages produced from the F2-generation had lower concentrations of IVDDM (P~0.01) and TNC (P~0.01) and higher concentrationsofNDF(P~0.0I),ADF(P~0.01),ADL(P=0.05)andCP(P=0.03) than those produced from the F,-generation. Similarly, acetic acid concentration of silages produced from the F,-generation maize was lower (PiO.01) than those produced from the F,-generation. The difference in silage acetic acid concentration between the F,- and F2-generations was greater (hybridxgeneration, P=O.O2) for the early-maturing hybrid than for the medium-maturing or late-maturing hybrid. Interactions between plant density and hybrid generation for IVDDM (P=O.O3) and ADF (P=O.O3) concentrations demonstrate that the F,-generation was less density-tolerant than the F,-generation of the hybrids (Fig. I ). This response may be related to the TNC concentration (densityxgeneration, P=O.OS), the pattern of which followed. that of IVDDM. Inasmuch as there were no interactions between hybrid generation and plant

J.R. RUSSELL ETAL.

20 TABLE

5

Year 2: effect of generation of hybrid on the total and grain yields, grain-io-stover ratios and composition of freshly harvested and ensiled maize herbage. Data show mean of three replications of three plant densilies. DM, IVDDM, NDF, ADF, ADL, TNC and CP are combined means of freshly harvested and ensiled herbages. Lactic, acetic and butyric acid are means of silages km

Yields (kg DM ha-‘) Herbage Grain

Grain-to-stovet

ratio

Hybrid generatian

Relative (h)

(g)

Early

Medium

Late

FI FZ F, FZ

14257 11724 7055 5370

I5811 14855 7118 5762

21140 14715 10296 6560

F, F2

DM (gkg-‘)

Proponion IVDDM NDF ADF ADL TNC

F, F1

FI F, F, F, F, F2 F, F2 FI F, FZ

Lactic acid Acelic acid Butyric

acid

of hybrid

0.85 0.66

SEM

0.96 0.85

Significance

h

g

1543.3

co.01


0.02

838.1

co.01


0.04

~0.01


0.70


0.22

0.47

0.096

bxg

520 482

419 424

470 451

29.7

763 717 485 586 221 252

739 741 504 554 234 236 46 44 321 319 62 73

777 734 454 532 205 229 40 4s 386 308 66 67

20. I

0.31

co.01

0.09

22.9

0.01


0.17

13.5

0.03


0.18

4.3

0.02

0.05

0.16

31.1

0.11


0.08

3.9

‘zo.01

0.03

0.08

4.6

0.14

0.12

0.06

I.2

0.24

0.19

0.62

of DM (g kg-‘)

h CP

0.99 0.86

maturity

F, F2 FI F, F, F2

45 54 345 273 73 74 35 46 II 17 0. I 0.0

47 44 I2 13 0.2 0.0

42 44 I2 14 0.0 0.3

co.01 0.48

0.02 0.49

density for herbage yield, grain yield or grain-to-stover ratio, the interactions between hybrid generation and plant density on herbage composition were unrelated to TNC translocation to the grain. There was also an interaction between plant density and generation for the lactic acid concentrations (P
21

Fig. I. In vitro digestible dry matter and acid detergent fiber concentrations of F,- and Fz-generaiions of hybrids grown at three plant densities.

TABLE 6 Significant (P
Intercept @kg-’ DM)

Slope Variable

Coeflicient

Significance

r’

Fresh1.vhoi-vessrcd I

969.9

ADF

-0.94


0.65

2

987.5

ADF ADL

-0.86 - 1.02


0.69

3

908.0

ADF ADL TNC

-0.73 -0.86 I.21


0.71

1004.5

ADF

-1.09


0.45

893.7

ADF NDF

-1.06 0.23


0.49

Emled I

2

J.R. R”SSEt.t. ET AL.

22 TABLE

7

Significant (P
r’

-0.063

P
0.28

-0.046 -0.055

P
0.36

SlOPC

Model

I

70.6

2

104.4

Variable

Coeffkient

DM DM IVDDM

and 8.9 plants m-* were 4.6 g kg-’ DM lower, 0.7 g kg-’ DM lower, and 14.4 kg- I DM greater than those produced from the F,-generations of the hybrids. Regressions predicting IVDDM and lactic acid concentrations

In freshly harvested herbage, concentrations of ADF, ADL and TNC were selected (PO.16). Dry matter and IVDDM concentrations of freshly harvested herbages were selected (PC 0.10) by stepwise regression to predict the lactic acid concentration of the resulting silages (P~0.36; Table 7). CONCLUSIONS

Results of this experiment imply that grain-to-stover ratios of maize herbage from 0.66 to 1.26 do not greatly influence the digestibility of freshly harvested or ensiled maize herbage. Therefore, management practices that increase herbage yield, such as using late-maturing hybrids, planting at densities as high as 8.9 plants m-’ or harvesting at physiological maturity, will not greatly decrease maize silage digestibility, even though they may alter the grain-to-stover ratio. Similarly, utilizing the F,-generation of the maize hybrids decreased the grain-to-stover ratio of the forage while having only small

MAlZE

HERBAGE:

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“.ALUE AND ENSlLlNG

YROPERTlES

23

particularly when grown at plant densities of 6.9 plants m-2 or less. The low digestibility and high ADF concentration of Frgeneration maize grown at high plant density, however, indicated reduced density tolerance, a trait that would need to be considered ifthe F,-generation were used as seed for corn silage production. The higher lactic acid concentrations in maize silage from late-maturing hybrids and earlier harvest dates would seem advantageous for silage preservation. Intake of maize silage by cattle (Huber et al., 1965) and sheep (Marten et al., 1976), however, has been reported to be positively correlated with silage DM concentration; thus, reduced animal performance may resu!t from ?he low DM concentrations of these silages. effects on its digestibility,

ACKNOWLEDGMENTS

The authors gratefully acknowledge the assistance of W.R. Akin, ES. Gregory, B.A. Kuehl and Dr. D.F. Cox in the conduct and analysis of this experiment. This is journal paper No. J-14270 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, Project No. 2373.

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