Nitrogen use efficiency and grain yield of corn hybrids as affected by nitrogen rates and sowing dates in subtropical environment

Delay of sowing date in subtropical environments with long growing seasons can modify the yield response of corn hybrids to nitrogen (N) fertilization. This study evaluated the effects of the sowing time, and N top-dress rate on corn hybrids’ yield and N-use efficiency with different cycles. Two field experiments were carried out in subtropical environment of southern Brazil. The following factors were investigated: corn hybrids (AG9025, super early cycle and P30F53, early cycle), sowing times (early and late spring), and N top-dress rates (0, 150, 300 and 450 kg ha). The delay of sowing date from early to late spring reduced 10 % the number of kernels per ear, decreasing grain yield. Corn presented lower yield potential in late sowings (-24 %), associated with a smaller response of grain yield to the N rate increase. The maximum corn yield was achieved at a rate of 360 kg ha of N in early spring sowing and 300 kg ha in late spring. The hybrid with early cycle presented greater yield stability and higher N use efficiency than the super early cycle hybrid in the late sowing. The N agronomic efficiency use is 47 % lower in late spring sowing than in early spring sowing. Regardless of the sowing date, the N use efficiency decreased 0.08 for each kg ha N rate increase. This study suggests a reduction of at least 20 % in the N top-dress rate when the sowing date of corn is delayed to late spring in southern Brazil to decrease N losses and production costs.