214. Effect of Planting Density and Cutting Height on Dry Matter Yield and Forage Quality of Corn and Sorghum Silages.

Abstract Corn and forage sorghum are widely used as silage crops in dairy and beef production systems due to their high biomass yields and favorable fermentation characteristics. Management practices such as planting density and cutting height have been shown to independently influence forage production and nutritive value; however, few studies have evaluated their combined interaction. The objective of this study was to evaluate the effects of cutting height, using two conventional (Conv) and two brown-midrib (BMR) corn and sorghum hybrids, and planting population on forage dry-matter (DM) yield, silage quality, and in-situ fiber digestibility. Forages were planted in two fields (64 plots per field) with contrasting yield potential at two theoretical planting densities (low: 59,000 and 124,000 seeds per hectare for corn and sorghum, respectively; high: 120,0000 and 247,000 seeds per hectare for corn and sorghum, respectively). Corn and sorghum plots were harvested at either a low cutting height (178 mm) or a high cutting height (483 mm). No interaction between planting density and cutting height was observed for the reported variables. Planting density had no effect on DM yield (P = 0.08), neutral detergent fiber (NDF; P = 0.06), or acid detergent lignin (ADL; P = 0.22); however, there was a reduction in stem width when forages were planted at a higher density (14.9 vs. 17.2 mm; P < 0.01). Conventional hybrids yielded more than BMR hybrids (22,105 vs. 18,419 kg DM/ha; P < 0.01), though the magnitude of this difference varied across the two planting densities. Cutting height had a significant effect on DM yield, with higher yields observed at lower cutting heights (21,670 vs.18,854; P < 0.01), largely driven by forage sorghum. Forage NDF (44.24 vs. 45.55; P = 0.01) and ADL (3.32 vs. 3.44; P = 0.02) were lower when plants were cut at a higher height. Furthermore, cutting height had a significant effect on in-situ indigestible NDF (uNDF), with lower cutting height forages having greater uNDF (14.4 vs. 13.3% DM; P = 0.01). In addition, the yield of potentially degradable NDF was 14% higher at low cutting heights than at higher cutting heights (6,696 vs. 5,747 kg/ha, respectively). In conclusion, increasing cutting height decreased forage yield and affected the nutritional composition and fiber digestibility of corn and sorghum silage, but was minimally affected by planting population.