Assessment of planting soil temperature and GDD impacts on silage corn (Zea mays L.) biomass

The annual forage crop production system, enclosing silage corn (<italic>Zea mays</italic> L.) and following cool-season annual forage, can enhance forage production efficiency where available land is limited for pasture production. In this forage production system, successful silage corn cultivation has a significant value due to the great yield of highly digestible forage. However, some untimely planting or harvesting of corn due to changing weather often reduces biomass and feeding values. Therefore, a study was conducted to quantify the corn silage biomass reductions by the deviations from optimum planting soil temperature and optimum growing degree day. The approximations of maximum corn production were estimated based on field trial data conducted between 1978 and 2018 with early, medium, and late-maturity corn groups. Based on weather data, the recorded planting dates and harvest dates were converted into the corresponding trials’ soil temperatures at planting (STP) and the growing degree days (GDD). The silage corn biomass data were regressed against STP and GDD using a quadratic function. The maximum biomass point was modeled in a convex upward quadratic yield curve and the optimum STP and GDD were defined as those values at the maximum biomass for each maturity group. Optimized STP was at 16.6, 16.2, and 15.6°C for early, medium, and late maturity corn groups, respectively, while optimized GDD at harvest was at 1424, 1363, and 1542 °C. The biomass reductions demonstrated quadratic functions by the departures of STP or GDD. The 5% reductions were anticipated when STP departed from the optimum temperature by 2.2, 2.4, and 1.4°C for early, medium, and late maturity corns, respectively; the same degree of reductions were estimated when the GDD departed by 200, 180, and 130°C in the same order of the maturity groups. This result indicates that biomass reductions of late-maturity corn were more sensitive to the departures of STP or GDD than the early-maturity corn. Therefore, early maturing cultivars are more stable in biomass production in a silage corn–winter annual forage crop production system to enhance forage-based livestock production efficiency.