Effects of seeding rate and hybrid relative maturity on yield, nutrient composition, ruminal in vitro neutral detergent fiber digestibility, and predicted milk yield of dairy cows in whole-plant corn forage in subtropical conditions

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We aimed to evaluate the effects of season (SEA), relative maturity (RM), and seeding rate (SR) on yield, nutrient composition, ruminal in vitro NDF digestibility at 30 h, and predicted milk yield in whole-plant corn forage grown in subtropical regions. During the summer of 2016 and spring of 2017, 3 hybrids varying in RM [118 (RM118); 124 (RM124); and 130 (RM130) d] were planted at 2 different SR [63,000 (63K) or 73,000 (73K) plants/ha] in a randomized complete block design with 4 blocks. Data were analyzed as a 2 (SEA) × 3 (hybrid RM) × 2 (SR) factorial using linear mixed model procedures, where hybrid RM, SR, SEA, and all their interactions were fixed effects, and block was the sole random effect. A 3-way interaction was observed for DM yield, which was greatest (18.0 Mg/ha) for RM130 planted at 63K for summer and RM130 planted at 73K (27.0 Mg/ha) for spring. Later RM hybrids had lower starch concentration and yield, but both were also influenced by season. The NDF concentration was lowest for hybrid RM118. The NDF and TDN yield were both greater for the spring season compared with the summer, but both were influenced by SR. Predicted milk yield per megagram of forage (kg/Mg) and starch yield were both lowest when planted at 63K for hybrid RM130. Greater NDF and lower undigested NDF concentrations were observed in 63K compared with 73K for SR. Seeding rate can be used to increase DM yield, but yield is also affected by hybrid RM and season. Hybrid RM can also be used to increase DM yield with later RM or improve nutrient composition with an earlier RM hybrid by increasing starch concentration and decreasing NDF concentration. Additionally, the greater starch concentration combined with the greater DM yield observed for treatments in the spring season suggest producers should focus their efforts on growing the bulk of corn silage during the spring. Last, different levels of SR and different hybrid RM combinations can be used during different seasons to maximize corn silage productivity.