Assessing yield and nutritive value of corn varieties for silage production carrying the brachytic2 mutation harvested at different stages of maturity

The aim of this study was to evaluate the forage feeding value of short-stature corn (SSC) genotype characterized by a brachytic2 (i.e., br2) mutation in comparison to tall-stature corn genotype (TSC) harvested at 5 different harvest moments (HM; i.e., 114, 119, 125, 135, and 149 d). In particular, 5 corn varieties selected for whole-plant silage were grown in an experimental field and harvested at 5 different HM. The field was divided into 15 experimental plots (30 m long × 4 rows × 0.75 m spacing between rows, with 1 row empty as a buffer zone); each variety was randomly seeded in 3 plots of experimental field. Notably, 2 corn varieties of TSC genotype (i.e., DKC7023 and DKC6731, respectively) were grown at a density rate of 9 plants/m2, whereas 3 corn varieties of SSC genotype (i.e., DKC6648SC, DKC6646SC, and DKC7236SC, respectively) were grown at a density rate of 13 plants/m2. The HM were based on the accumulated growing degree days values of 1,096, 1,172, 1,246, 1,398, and 1,596 (°C) using a 10°C base temperature. Data were analyzed as a split-plot in a randomized complete block design with 3 blocks (i.e., replicates) and 5 treatments (TRT). The whole-plot was TRT (i.e., 3 SSC and 2 TSC) and the subplot was maturity (HM; i.e., 114, 119, 125, 135, and 149 d after planting). An a priori contrast comparing SSC (3 varieties) and TSC (2 varieties) was run to evaluate the overall effect of genotype. Specific orthogonal contrasts were applied to evaluate linear and quadratic trends across HM. Interaction between HM and TRT showed significant effect on fresh yield and DM yield. Fresh yield decreased with the advance of maturity stage; however, DM yield increased among the HM. Fibrous fractions decreased with the advance of maturity. On average, SSC varieties had lower NDF, ADF, and ADL concentrations in comparison to TSC. Starch concentration increased with the advance of maturity stage, peaking at 149 d (i.e., 39.1% DM). Starch content was higher for SSC by 12.7% in comparison to TSC. The estimated energy content (i.e., kg milk/t DM) was different among genotypes, with SSC being characterized by higher value than TSC. A quadratic effect for in vitro NDF digestibility at 12 and 24 h after incubation was observed within the HM. In contrast, NDF digestibility linearly decreased after 30 h incubation with increasing HM. Varieties characterized by SSC genotype had higher NDF digestibility at 30, 48, and 120 h after incubation in comparison to TSC. The in situ starch disappearance (isSD) linearly decreased with increasing HM. The SSC had higher isSD compared with TSC. Concluding, cropping SSC may be a feasible strategy, in terms of agronomic response and nutritional composition, to maximize silage nutritional quality through greater starch concentration, lower fiber concentration, and improved starch and NDF digestibility, while maintaining similar DM yield with respect to TSC. Further studies are warranted to elucidate the agronomical advantages of these new corn hybrids.