Effects of planting population, genotype, and nitrogen fertilization on dry matter yield, nutrient composition, in vitro ruminal neutral detergent fiber disappearance, and nitrogen and phosphorus removal of corn for silage

The objective of this study was to evaluate the effects of corn planting population with different fertilization rates on forage dry matter (DM) yield, silage quality and digestibility, and nutrient removal from the soil in a commercial dairy farm. The study was performed in 2 fields during the springs of 2017 and 2018 at a 425-cow commercial dairy farm located in Crockett, Virginia (USA). Conventional (CONV) and brown midrib (BMR) corn genotypes were planted at a theoretical planting population of 60,000, 75,000, and 90,000 seeds/ha (60 K, 75 K, and 90 K, respectively). Four plots were planted for each planting population and genotype in each field during each year. In addition to pre-planting (200 kg N/ha) and planting (55 kg N/ha) fertilization, plots were fertilized with 50 or 100 kg N/ha when the crop showed 6 visible leaves (V6). Resulting populations were 63,200, 72,600, and 86,300 plants/ha for 60 K, 75 K, and 90 K, respectively. Planting corn at 90 K resulted in the greatest DM yield (21.4 Mg/ha), whereas DM yield was similar for 75 K and 60 K (20.3 Mg/ha). An interaction between planting population and year existed for DM yield. Doubling the dosage of N fertilizer at V6 increased biomass yield only by 3.1 %. Even though the number of kernels per plant increased with double N fertilization, an interaction did not exist between corn planting population and N fertilization. The CONV corn yielded 19.2 % more than the BMR corn (22.5 vs. 18.9 Mg/ha, respectively). Planting population affected the concentrations of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and phosphorus (P), although the magnitudes of these changes have minor nutritional or productive implications. Also, planting population did not affect the concentrations of ash, starch, and sugars. Planting corn at 60 K resulted in the greatest concentration of P (2,661 mg P/kg DM), whereas the concentration of P was similar for 75 K and 90 K (2,566 and 2,552 mg P/kg, respectively). Neither corn planting population or N fertilization affected in vitro dry matter digestibility (IVDMD) or in vitro neutral detergent fiber digestibility (IVNDFD). In conclusion, increasing corn planting population and N fertilization had minimal or no effects on corn silage composition and digestibility. Future studies should directly evaluate the interaction between corn planting population and crop maturity on DM yield and on nutrient composition and digestibility of corn for silage.