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Production Papers

Timing Corn Forage Harvest for Bunker Silos

Department of Crop and Soil Sciences, 609 Bradfield Hall, Cornell Univ., Ithaca, NY 14853

^* Corresponding author (wjc3{at}cornell.edu)

Received for publication April 28, 2004.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Dairy producers with large operations have switched from upright to bunker silos so they begin corn (Zea mays L.) forage harvest at 300 g kg^–1 instead of 350 g kg^–1 dry matter (DM) content. Three hybrids were harvested at average DM contents of 295, 310, and 350 g kg^–1 to compare DM yield and forage quality of corn forage typical of bunker and upright silos. Hybrid and DM content did not have interactions for DM yield and forage quality characteristics. The DM content at harvest did not affect DM yield (14.6, 15.0, and 15.1 Mg ha^–1 at 295, 310, and 350 g kg^–1, respectively). As DM content increased, neutral detergent fiber (NDF) declined (469, 447, and 417 g kg^–1, respectively), but NDF digestibility (657, 632, and 631 g kg^–1) and crude protein (78, 73, and 72 g kg^–1) declined only from 295 to 310 g kg^–1. As DM content increased, milk per megagram, a forage quality index, increased (1622, 1699, and 1764 kg Mg^–1 respectively), but in vitro true digestibility (IVTD) increased (839, 835, and 847 g kg^–1), only from 310 to 350 g kg^–1. Calculated milk yields differed at DM contents of 295 (24380 kg ha^–1) vs. 350 g kg^–1 (26947 kg ha^–1) but not at 310 g kg^–1 (25727 kg ha^–1). Results from this study indicate that dairy producers with bunker silos do not compromise DM and calculated milk yields, despite somewhat lower forage quality, if they begin harvest at 310 g kg^–1 DM content.

Abbreviations: CP, crude protein • DM, dry matter • GDD, growing degree days • IVTD, in vitro true digestibility • NDF, neutral detergent fiber • RM, relative maturity

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
A HORIZONTAL OR BUNKER SILO is the most economical silage storage system on a cost per silage unit basis (McGilliard et al., 1987). As dairy operations increased in size in the late 1980s and 1990s, dairy farmers built bunker silos to meet the additional silage requirement for the increased cow (Bos sp.) numbers. The bunker silo is now the main method for storing silage on large farms (Savoie and Jofriet, 2003). Dairy producers with bunker silos typically begin corn silage harvest at DM contents at about 300 g kg^–1, about 50 g kg^–1 wetter than when they filled upright silos, because silage effluent production from bunker silos is minimal at DM contents of 300 g kg^–1 (Bastiman and Altman, 1985). Dairy farmers who use bunker storage systems question if DM yield and forage quality are compromised when harvesting corn silage at 300 instead of 350 g kg^–1 DM content.

Hunt et al. (1989) reported that corn DM yield and quality were greater at 315 vs. 390 g kg^–1 DM content in an irrigated California study. Wiersma et al. (1993) reported that DM yields and in vitro dry matter digestibility of corn forage were greater at 330 vs. 260 g kg^–1 DM content in a Wisconsin study. In another Wisconsin study, Darby and Lauer (2002) reported that optimum DM yield of corn occurred at about 420 g kg^–1 DM content. In the same study, optimum forage quality, as measured by milk per megagram (Schwab and Shaver, 2001), and calculated milk yields (Schwab and Shaver, 2001) occurred at DM contents of 330 and 370 g kg^–1, respectively. Based on these studies, dairy producers may sacrifice yield and quality by filling bunker silos at DM contents of 300 instead of 350 g kg^–1. Darby and Lauer (2002), however, concluded that DM yield, quality, and milk yields will remain at 95% of optimum between DM contents of 300 and 400 g kg^–1. Lewis et al. (2004) also reported that calculated milk yields did not vary between 280 and 420 g kg^–1 DM content because the decline in corn forage quality was offset by an increase in DM yield as DM content increased.

Dairy producers who harvest more than 200 ha of corn silage typically have bunker silos as a storage system and begin harvest at DM contents just above or even just below 300 g kg^–1. We evaluated DM yield, forage quality, and calculated milk yields of three corn hybrids at DM contents of about 295, 310, and 350 g kg^–1. The objective of the study was to determine if DM yield and forage quality are compromised when beginning corn silage harvest at DM contents typical for bunker vs. upright silo storage systems.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments were conducted in 2002 and 2003 on a Honeoye silt loam soil (fine-loamy, mixed, mesic Glossoboric Hapludalfs) at a Cornell University research farm near Aurora, NY (42°26' N lat, 76°26' W long). The experimental site is tile-drained, and soil test values indicated a pH of 7.8 and high concentrations of P and K in each year. The experimental site, which was plowed and harrow-cultipacked in April of each year, has been in a corn–soybean [Glycine max (L.) Merr.] rotation since 1990, so corn followed soybean in each year. The experimental site received about 90 kg ha^–1 of broadcast K (0–0–62) in April before plowing. Also, 90 kg ha^–1 of liquid starter fertilizer, 40–61–0, was banded at planting. Atrazine (2-chloro-4 ethylamino-6-isopropylamino-1,3,5-triazin) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were applied immediately following planting for weed control. Escapes were controlled by hand weeding. At the fifth leaf stage, 150 kg N ha^–1 was side-dressed (injected 0.1 m deep between every other row) as a 32% (wt./vol.) N solution of urea [(NH₂)₂CO] and ammonium nitrate (NH₄NO₃).

Three hybrids were planted in late April of both years with a four row planter at 0.76 m row spacing at 86000 kernels ha^–1. Plots were thinned, if necessary, to a final plant density of 79000 plants ha^–1. The hybrids included Pioneer Brand ‘34B23" (dual-purpose), 108-d RM; Mycogen Brand ‘TMF108’ (leafy), 108-d RM; and Cargill Brand ‘F757’ (brown midrib), 114-d RM. The experimental design was a randomized complete block with four replications in a split-plot arrangement with hybrids as main plots (30.3 by 3.1 m), and DM contents at harvest as subplots (10.1 by 3.1 m). The center two rows of each hybrid were harvested by hand at three DM contents to determine DM yield. Each hybrid was sampled for DM content (oven-drying) a couple of days before harvest to ensure that each hybrid approximated the intended DM contents of about 295, 310, and 350 g kg^–1 34B23 and TMF108 were harvested on the same dates in 2002 (23, 26, and 30 August) and F757 was harvested on 30 August, and 4 and 8 September. In 2003, TMF108 (29 August, and 5 and 11 September), 34B23 (2, 6, and 13 September), and F757 (5, 11, and 18 September) were harvested on separate dates. The average DM content of 34B23 (294, 306, and 350 g kg^–1), TMF108 (311, 322, and 355 g kg^–1), and F757 (282, 303, and 339 g kg^–1), when averaged across years, was very close to the intended DM contents. The DM content of individual hybrids, however, varied by as much as ±15 g kg^–1 in each year because of the difficulty in timing a harvest to a specific DM content.

Five plants were randomly selected at harvest from each subplot to estimate DM content and forage quality characteristics. The five plant sample was ground through a chipper-shredder in the field and an approximate 1-kg subsample was taken from the shredded material and dried at 60°C in a forced-air dryer to constant moisture. The subsample was then further ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) fitted with a 1-mm screen.

Subsamples (0.5 g each) were analyzed by wet chemistry for NDF, using the ANKOM system (ANKOM Technology, Fairport, NY) according to procedures by Van Soest et al. (1991), and for total N using a Leco FP528 N analyzer (LECO Corp., St. Joseph, MI) with Dumas combustion (Tate, 1994; Wiles et al., 1998). The crude protein (CP) concentration was calculated by multiplying N by 6.25. Subsamples (0.25 g each) were also analyzed for IVTD according to Stage 1 of the procedure described by Marten and Barnes (1980), using a 48-h incubation period at 39°C in 5 mL of buffered rumen fluid containing 20 mL of the Kansas State buffer supplemented with 0.5 g L^–1 urea. In vitro fiber digestibility was determined according to Cherney et al. (1997), using the rumen buffer described by Marten and Barnes (1980) and using the Daisy II^200/220 in vitro incubator (ANKOM Technology, Fairport, NY) and the ANKOM^200/220 fiber analyzer. The buffer contained urea. Ruminal fluid inoculum was obtained from a nonlactating, rumen-fistulated Holstein cow, offered a medium quality orchardgrass (Dactylis glomerata L.) hay diet for ad libitum intake. Digestibiity samples (0.25 g) were incubated in duplicate for 48 h at 39°C, and undigested residues were treated with neutral detergent solution.

Subsamples (1.0 g) were also analyzed for ash content by combustion at 510°C for 4 h. Subsamples (0.1 g) were analyzed for starch by Dairy One (DHI Forage Testing Lab, Ithaca, NY). The subsamples were pre-extracted for sugars, then a glucoamylase enzyme was used to hydrolyze starch to dextrose. The subsamples were then injected into a YSI 2700 SELECT Biochemistry Analyzer, where dextrose is oxidized to hydrogen peroxide and lactose. Hydrogen peroxide is detected by an electrode, and current at the electrode is directly proportional to hydrogen peroxide concentration, which is directly related to dextrose and starch concentrations.

Potential milk yield indices were then estimated from the spreadsheet, Milk 2000 (Schwab and Shaver, 2001). Milk Mg^–1 (kg milk Mg^–1 corn forage), a forage quality index, was calculated from NDF, NDF digestibility, CP, ash, and starch concentrations. Milk yield (kg milk ha^–1 corn forage) was calculated as the product of milk Mg^–1 and DM yields.

Hybrid, and DM content at harvest were considered fixed, and replications and years were considered random effects in the analysis of variance. Combined analyses across years and separate analyses within a year were conducted for DM yield, forage quality characteristics, milk Mg^–1, and milk yield using General Linear Model (GLM) procedures of the SAS statistical package, version 7.0 software (SAS Inst., 1998). The Bartlett test for homogeneity of variances was conducted on all variables as outlined by procedures in Anderson and McLean (1974). All variables had homogenous variances, when tested at = 0.05. Consequently, we will present the combined analyses. All effects in the combined analyses were considered significant at = 0.05. Fisher's protected LSD (P = 0.05) was used to separate means when main effects tested significant.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
A wet May and June with normal temperatures followed by a very dry July and August with warm temperatures characterized the 2002 growing season (Table 1). Visible leaf wilting was observed from late July through harvest in 2002. A cool May and June with normal precipitation followed by a cool July with very wet conditions and a warm August with dry conditions characterized the 2003 growing season. Visible leaf wilting was observed during the last week of August in 2003. The experimental site received 31 mm of precipitation on 1 September, which relieved the dry conditions. The dry warm conditions in August resulted in premature stover senescence in both years. Consequently, the 108 to 114 d RM hybrids were harvested about 3 wk earlier than normal in 2002 and about 1 wk earlier than normal in 2003. Weather conditions also contributed to below-average DM yields in 2002 (11.0 Mg ha^–1) and above-average DM yields in 2003 (18.9 Mg ha^–1).

When averaged across hybrids, starch concentrations increased almost 100 g kg^–1 as DM contents increased from 295 to 350 g kg^–1 (Table 3), which is consistent with the results of Bal et al. (1997). Starch concentrations in this study averaged less than normal because the dry July and August conditions resulted in poor kernel set and low starch concentrations in 2002 (170 g kg^–1) vs. 2003 (283 g kg^–1). The F757 hybrid had 40 to 50 g kg^–1 lower starch concentrations compared with the other hybrids in this study, in part because it silked 1 wk later so was more susceptible to poor kernel set and less grain-filling in the dry August conditions. Unlike NDF, starch digestibility does not change between DM contents of 300 and 350 g kg^–1 (Bal et al., 1997; Johnson et al., 2002). Consequently, lower starch concentration at 295 g kg^–1 DM content can reduce energy density of corn silage and milk production of cows.

When averaged across hybrids, CP declined 5 g kg^–1 as DM content increased from 295 to 310 g kg^–1 but declined no further at 350 g kg (Table 3). Wiersma et al. (1993) and Darby and Lauer (2002) reported a linear decline in CP as DM contents increased from about 250 to 400 g kg^–1, mainly because DM yields increased, which diluted the N concentration of the silage. The F757 hybrid had greater CP concentrations when compared with 34B23 and TMF108, which is consistent with a previous study in which brown midrib hybrids had greater CP concentrations when compared with other hybrids (Cox and Cherney, 2001). High CP concentrations in corn silage, however, does not consistently result in improved animal performance (Oba and Allen, 2000; Greenfield et al., 2001).

When averaged across hybrids, ash concentrations decreased 5 g kg^–1 as DM content increased from 295 to 350 g kg^–1 (Table 3). All three hybrids differed in ash concentrations with 34B23 averaging 6 g kg^–1 less than TMF108. It is assumed that corn hybrids have similar ash concentrations of about 45 g kg^–1 (Schwab and Shaver, 2001). It is not clear why ash concentrations averaged 29 g kg^–1 (32 g kg^–1 in 2002 and 26 g kg^–1in 2003) and why 34B23 averaged 6 g kg^–1 less when compared with the other hybrids in this study.

Milk Mg^–1, a forage quality index, increased about 70 kg Mg^–1 with each increase in DM content (Table 4). The increase in starch concentration and decrease in NDF and ash concentrations offset the decline or lack of change in NDF digestibility and CP concentrations resulting in maximum milk Mg^–1 at 350 g kg^–1 DM content. The results from this study indicate that forage quality can be lower in bunker vs. upright silos if corn is harvested at typical DM contents for each storage system. Darby and Lauer (2002), however, reported optimum milk Mg^–1 at 300 g kg^–1 DM content, and Lewis et al. (2004) reported no difference in milk Mg^–1 at DM contents of 280 and 350 g kg^–1. As expected, F757, the brown midrib hybrid, had the greatest milk Mg^–1 because of much greater NDF digestibility and CP concentrations.

When averaged across hybrids, DM yields did not differ across DM contents at harvest (Table 5). Generally, DM yields increase from about 300 to 400 g kg^–1 DM content (Hunt et al., 1989; Ganoe and Roth, 1992; Darby and Lauer, 2002; Lewis et al., 2004), but Wiersma et al. (1993) reported maximum DM yields at 330 g kg^–1 DM content and Lewis et al. (2004) reported no DM yield differences at 280 and 350 g kg^–1 DM content. The F757 hybrid yielded about 12% less than the other two hybrids, which is less than the 20% yield difference between brown midrib and other hybrid types of similar maturity reported by Cox and Cherney (2001). The F757 hybrid is 6 to 8 d longer in RM compared with 34B23 and TMF108, which increases its yield potential and probably contributed to only a 12% instead of the 20% yield penalty previously reported for brown midrib hybrids.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The results from this study indicate that dairy producers do not compromise DM yield or calculated milk yields when switching from bunker to upright silo storage systems if they begin harvest at 310 g kg^–1 DM content. Forage quality, however, may be somewhat less at 310 vs. 350 g kg^–1 DM content because of lower starch and greater NDF concentrations, especially when NDF digestibility does not differ between these DM contents. Some dairy producers in the Northeast, who harvest 500 ha of corn silage, begin harvest at DM contents just below 300 g kg^–1 to help avoid soil compaction with the heavy truckloads of silage during September, the wettest month in the Northeast. Nevertheless, we recommend that dairy producers in the Northeast USA begin corn silage harvest at 310 instead of 295 g kg^–1 DM content, even if it means a 7-d delay in harvest during the potentially wet September, because of the lower calculated milk yields at 295 g kg^–1 DM content.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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This Article Abstract Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Cox, W. J. Articles by Cherney, J. H. Search for Related Content PubMed Articles by Cox, W. J. Articles by Cherney, J. H. Agricola Articles by Cox, W. J. Articles by Cherney, J. H. Related Collections Crop Growth and Development Maize Production Agriculture Maize Management