协调水稻产量和品质的植株临界氮浓度的确定

根据植株氮营养状况指导优质米生产具有重要意义。试验以五优稻4号为供试材料，以密度为主区（密度分别为每平方米18穴和25穴），氮量为副区（氮量分别为0、75、105、135 kg hm?2），测定水稻植株全氮、籽粒无机氮含量、水稻产量和品质等指标，以期为实现水稻丰产优质提供理论依据。结果表明:施氮量和水稻产量呈2次曲线关系，最高产量施氮量为113 ~ 119 kg hm?2，经济合理施氮量为110 ~ 116 kg hm?2；随着施氮量增加，各个时期水稻植株含氮量，收获期籽粒铵态氮和硝态氮含量显著提高，N105处理与N0处理间上述指标差异均显著（P < 0.05），而 N105和N135处理间只有籽粒无机氮含量差异显著；施氮后籽粒蛋白质含量有增加趋势，随着施氮量增加稻米食味值下降，N135处理食味降低超过10%（P < 0.05），其他处理间差异不显著。密度增加，水稻氮素积累量增加，产量提高了11.4%；稀植有利于提高地上部含氮量、籽粒铵态氮和硝态氮含量；稀植出米率提高了4.77个百分点（P < 0.05），食味值有降低趋势。根据肥料效应函数以及施氮量和植株含氮量关系函数，拔节期和抽穗期，D1密度下植株临界氮浓度分别为15.26 ~ 16.18 g kg?1和22.65 ~ 25.98 g kg?1，D2密度下对应值分别为11.71 ~ 12.94 g kg?1和20.73 ~ 23.24 g kg?1。上述结果表明，合理密植有利于水稻高产，氮量过高不利于水稻高产和优质。在水稻丰产和优质的情况下，氮肥用量在91 ~ 105 kg hm?2比较合适，抽穗期叶片含氮量24.82 ~ 25.98 g kg?1（D1）和22.18 ~ 23.24 g kg?1（D2）可以作为协同实现水稻丰产优质的诊断指标。

Determination of Critical Nitrogen Concentration for Coordinating Yield and Quality of Rice

It is important for the production of rice with high yield and good quality according to plant nitrogen (N) content. In this experiment, transplanting density was set as the main plot (transplanting density of D1 and D2 was 18 and 25 hills m?2, respectively), and N rates were set as the sub plots (N amounts of N0, N75, N105 and N135 were 0, 75, 105 and 135 kg hm?2, respectively). The contents of total N and grain inorganic N, yield and quality of rice (Wuyoudao 4) were determined. The results showed that there was quadratic curve relationship between N fertilizer dosage and rice yield. The N application rate with highest yield was 113-119 kg hm?2, the N application rate with maximum profit was 110-116 kg hm?2. The N content of rice plants at each period, the contents of ammonium N and nitrate N of grain at the harvest period were increased significantly with the increase of N application amounts and were significantly different between N105 and N0 treatments (P < 0.05).The inorganic N content was significantly different between N105 and N135 treatments. There was an increased trend of grain protein content after N application, but their difference was not clear between treatments. The rice taste value was decreased with the increase of N dosage, and was decreased by more than 10% in N135 treatment (P < 0.05). Compared to low density, the yield of high density was increased by 11.4%. However, low density increased the concentrations of plant N, ammonium N and nitrate N of grain. The milled rice rate of low density was increased by 4.77 percentage point (P < 0.05) compared to high density, while the taste value was decreased. According to the fertilizer response function and the relationship between N rate and plant N content, the critical N concentration at jointing and heading stages was 15.26-16.18 g kg?1 and 22.65-25.98 g kg?1 in D1 treatment, and was 11.71-12.94 g kg?1 and 20.73-23.24 g kg?1 in D2 treatment, respectively. Increasing transplanting density was beneficial for high yield of rice, but excessive N was not. The optimal N rate was 91-105 kg ha?1, and the suitable leaf N concentration was 24.82-25.98 g kg?1 in D1 treatment and 22.18-23.24 g kg?1 in D2 treatment at heading stage, which could be used as a diagnostic index for high yield and quality of rice.