Long-term impact of gypsum and nitrogen levels on soil chemical properties and maize forage and grain yield under no-tillage in a subtropical region

Gypsum has been used in tropical and subtropical clayey soils under no-till to manage subsurface acidity, but its interaction with nitrogen (N) fertilization in maize (Zea mays L.) is still underexplored. The objectives of this study were to evaluate topdressing N rates (0, 100, and 200 kg N ha−1 named N0, N100, and N200, respectively) applied to maize over the 2016/2017 and 2017/2018 crop seasons in a gypsum experiment (0, 3, 6, 9, and 12 Mg ha−1) that started in 2009. Soil chemical attributes, forage yield at the milky grain stage, forage bromatological quality, nutrient content, apparent N recovery efficiency (RE), and grain yield were evaluated. Residual effects of gypsum were found through higher Ca2+ and S-SO42− levels and lower Mg2+ levels in deeper soil layers. Topdressing N increased the mineral N levels at depth. Forage biomass increased by 18% and 32% on average with N100 and N200, respectively. N rates increased the forage nutrient content of all evaluated elements (N, P, K, Ca, Mg, and S). Forage digestibility and protein content were improved by N rates. The rate of N100 presented higher RE, whereas forage and grain yield with N100 were equivalent to those with N200. Grain yield increased with the residual effect of gypsum in the absence of N fertilization in one growing season. The residual effect of gypsum associated with N fertilization on maize presented no synergistic effect on forage or grain yield, while topdressing N rates improved maize attributes.