Black oat (Avena strigosa) forage yield and quality under nitrogen fertilisation and long-term gypsum

Context The effect of long-term gypsum on nitrogen (N) responsiveness in black oat (Avena strigosa Schreb.) forage lacks information.Aims and methods This study evaluated interactions between different rates of N (0, 50 and 100kgNha−1) and gypsum (0, 3, 6, 9 and 12Mgha−1) on the yield, nutrition and bromatology of forage black oats in a long-term experiment using a no-till system (NTS) in a Ferralsol in southern Brazil.Key results There was an interaction between residual gypsum and N rate on biomass forage yield in 2015, but not for the 2016 growing season. In 2015, the rate of 100kgNha−1 increased yield by 10% in the absence of gypsum and by 30% at low-medium rates of residual-gypsum (3 and 6Mgha−1), but there was no response to high N rate under high gypsum rates (9 and 12Mgha−1). In 2016, a poor-growing season, a gypsum rate of 6Mgha−1 and N rate of 100kgha−1 independently improved forage yield by 5%. Gypsum application produced higher forage contents of N, P, K, Ca and S, and decreased Mg content. N-fertilisation increased the N, K, Ca, and Mg contents, but decreased P content and S concentration. Gypsum had no effect on forage bromatological quality, and even with equivalent forage yield between 50 and 100kgNha−1, only the high N rate improved some of the forage quality attributes in both years.Conclusions and implications Neither gypsum nor topdressing of N altered N use by black oat forage.