Nitrogen sufficiency index for estimating nitrogen fertilizer requirement of irrigated rice

ABSTRACT The proper nitrogen management is required to achieve high irrigated rice yield. This study aimed to determine the rice response to nitrogen topdressing doses and calibrate the chlorophyll meter reading. Three experiments were conducted in a randomized block design. In the first experiment, five N rates (0, 30, 60, 90, and 120 kg ha-1) were evaluated as the first, and 30 kg ha-1 N as the second topdressing, which were combined with the application of 30 kg ha-1 N as the first and five N rates, as the second topdressing. The other experiments assessed the application of 30 kg ha-1 of N, as the first, and four N rates (0, 40, 80, and 120 kg ha-1), as the second topdressing. There was a response to N application, with maximum technical efficiency reaching 33 kg ha-1 in the first and between 40 and 50 kg ha-1 in the second topdressing. The chlorophyll meter was sensitive to estimate the amount of N to be applied in topdressing, using the nitrogen sufficiency index (NSI). To each percent unit of NSI below 95%, one should apply 10 kg ha-1 of N as the first and 2-3 kg ha-1 of N as the second topdressing.

摘要：要实现灌溉水稻的高产，需实施合理的氮肥管理措施。本研究旨在明确水稻对氮肥追肥用量的响应规律，并校准叶绿素仪读数。本研究采用随机区组设计开展3组田间试验。第一组试验设置两种氮肥追肥组合：其一为以5个施氮梯度（0、30、60、90和120 kg·ha⁻¹）作为第一次追肥、30 kg·ha⁻¹作为第二次追肥；其二为以30 kg·ha⁻¹作为第一次追肥、5个施氮梯度作为第二次追肥。其余两组试验统一设置为以30 kg·ha⁻¹作为第一次追肥，4个施氮梯度（0、40、80和120 kg·ha⁻¹）作为第二次追肥。试验结果表明，施氮可显著提升水稻产量，第一次追肥达到最大技术效率的最优施氮量为33 kg·ha⁻¹，第二次追肥的最优施氮量区间为40~50 kg·ha⁻¹。本研究采用氮素充足指数（nitrogen sufficiency index, NSI），证实叶绿素仪可灵敏估算追肥所需的氮肥用量：当氮素充足指数每低于1个百分点（即低于95%）时，第一次追肥需施加10 kg·ha⁻¹氮肥，第二次追肥则需施加2~3 kg·ha⁻¹氮肥。