Abstract #79

# 79
Influence of plant population, hybrid relative maturity, and cutting height on yield, nutrient content, and digestibility in whole-plant corn forage.
L. F. Ferraretto*1, R. D. Shaver2, J. G. Lauer2, L. H. Brown3, J. P. Kennicker3, D. M. Taysom4, 1University of Florida, Gainesville, FL, 2University of Wisconsin-Madison, Madison, WI, 3Monsanto, St. Louis, MO, 4Dairyland Laboratories Inc, Arcadia, WI.

The objective of this study was to evaluate the effect of plant population, hybrid relative maturity, and cutting height on yield, nutrient composition and ruminal in vitro starch (ivSD; 7 h incubations on dried and 4 mm ground samples) and NDF (ivNDFD; 30 h incubations on dried and 1 mm ground samples) digestibility in whole-plant corn forage. Eight hybrids (4 early [ER; 94–99 d] and 4 late [LT; 105–108 d] maturity) were each planted at 4 different plant populations (64,000 [64K], 79,000 [79K], 94,000 [94K] or 109,000 [109K] plants/ha), in triplicate, and harvested at 2 cutting heights (15 [LO] or 60 [HI] cm). Data were analyzed as a split-plot design using Proc Mixed of SAS with the fixed effects of maturity, plant population, cutting height and their 2- and 3-way interactions. Hybrid and plant population × maturity × hybrid interaction were random effects. Except for greatest CP content for 64K and lowest for 109K (P = 0.001) or a trend (P = 0.09) for 1.3%-units greater ivNDFD for 94K than 64K, no effects of plant population on nutritive value were observed (P > 0.10). Yield of DM (t/ha) was (P = 0.001) greatest for 109K and 94K, and lowest for 64K. Milk production was reduced (P = 0.001) by 2248 kg/ha, on average, for 64K than other treatments. Hybrid maturity did not affect (P > 0.10) any parameter. Reduced (P = 0.001) ADF (21.4 vs. 24.6%), NDF (33.8 vs. 37.7%) lignin (3.2 vs. 3.7%) and undigested NDF after 240 h of incubation (10.5 vs. 12.4%) concentrations and corresponding increased ivNDFD (52.7 vs. 49.6% of NDF) were observed for HI. Furthermore, HI had greater starch content (P = 0.001; 41.7 vs. 37.5%) but not digestibility (P = 0.13). A hybrid maturity × cutting height interaction was observed (P < 0.05) for DM yield/ha and milk production/ha. Although HI had lower DM yield than LO for both maturities, the magnitude of the difference was exacerbated in LT hybrids (2.56 vs. 1.54 t of DM/ha). This led to a reduction of 1203 kg of milk/ha for HI in LT but not ER hybrids. Plant population affected yield but not quality of whole-plant corn forage. In addition, cutting height increased nutritive value but at the expense of reduced yield.

Key Words: corn silage, plant population, cutting height