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

ABSTRACT 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-1). 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-1 of N in early spring sowing and 300 kg ha-1 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-1 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.摘要：在生育期较长的亚热带环境中推迟玉米播种期，会改变玉米杂交品种对氮肥（nitrogen, N）施肥的产量响应。本研究评估了不同生育周期的玉米杂交品种的播种时间与氮肥追施速率对其产量及氮素利用效率（N-use efficiency）的影响。研究于巴西南部亚热带环境中开展了两场田间试验，考察的因素包括：玉米杂交品种（AG9025，超级早熟品种；P30F53，早熟品种）、播种时间（早春与晚春）以及氮肥追施速率（0、150、300与450 kg·ha⁻¹）。将播种期从早春推迟到晚春，可使每穗粒数减少10%，进而降低籽粒产量。晚春播种的玉米产量潜力较早春播种降低24%，且籽粒产量随氮肥施用量提升的响应幅度更小。早春播种时，玉米最高产量对应的氮肥施用量为360 kg·ha⁻¹；晚春播种时则为300 kg·ha⁻¹。在晚春播种条件下，早熟杂交品种相较于超级早熟杂交品种具有更高的产量稳定性与氮素利用效率。晚春播种的氮素农学利用率较早春播种降低47%。无论播种时间如何，每增加1 kg·ha⁻¹的氮肥施用量，氮素利用效率均下降0.08。本研究表明，在巴西南部地区将玉米播种期推迟至晚春时，氮肥追施速率至少应降低20%，以减少氮素损失并降低生产成本。