华中区域直播冬油菜临界氮浓度稀释曲线的建立与应用

【目的】明确华中区域直播冬油菜的氮素稀释曲线模型及其适用性,探讨以氮素营养指数评价油菜氮素营养状况的可行性。【方法】通过2015—2016和2016—2017两个年度设置的不同氮肥用量（2015—2016年度氮肥用量为0、60、120、180和240 kg N·hm ^-2,2016—2017年度氮肥用量为0、60、120、180、240、300和360 kg N·hm ^-2）的田间试验,研究不同氮肥用量下从苗期到花期油菜各生育时期地上部生物量和植株氮素含量变化,建立直播冬油菜地上部临界氮素浓度稀释曲线模型。并利用该模型和植株氮素含量计算氮素营养指数,明确氮肥用量对油菜植株各个时期氮素营养指数的影响,探究油菜产量和氮素营养指数的关系,确定各时期适宜的氮素营养指数。 【结果】氮肥施用显著增加油菜地上部生物量和氮素含量,不同氮肥处理间差异显著。直播冬油菜地上部临界氮素浓度和地上部生物量符合幂指数的关系（Ncnc=3.49DM ^-0.26）。该模型可以将独立的两个试验的氮限制和非氮限制组数据区分开,模型拟合的氮素浓度和植株实际氮素浓度线性相关,RMSE和n-RMSE分别为0.37和13%,模型具有较好的稳定性。在试验氮肥用量范围内,各点不同时期氮素营养指数随氮肥用量的增加而增加,且氮素营养指数对氮肥用量的响应与产量相似。氮肥施用显著增加油菜产量,尽管不同试验点直播冬油菜产量对氮肥用量的响应存在差异,但各点相对产量和不同时期的氮素营养指数均呈一元二次曲线关系,各生育时期氮素营养指数可以准确地反映油菜氮素营养状况。直播冬油菜相对产量为1时,越冬期、薹期和花期的氮素营养指数分别为1.35、1.26和1.03。 【结论】油菜氮素稀释曲线模型Ncnc=3.49DM ^-0.26和氮营养指数能够评价华中区域直播冬油菜氮素营养状况,用于植株氮素诊断。

Determination and Application of a Critical Nitrogen Dilution Curve for Direct-Sowing Winter Oilseed Rape in Central China

【Objective】This study was conducted to determine the critical nitrogen (N) dilution curve for direct-sowing winter oilseed rape in Central China and its applicability, and the feasibility of N nutrition index (NNI) in evaluating N nutrition status of oilseed rape plant. 【Method】 Field experiments during 2015-2016 and 2016-2017 were conducted with different N application rates, including 0, 60, 120, 180 and 240 kg N·hm ^-2 during 2015-2016, and 0, 60, 120, 180, 240, 300 and 360 kg N·hm ^-2 during 2016-2017. The shoot dry matter and N concentration from seedling to flowering were studied. The model of the critical N concentration dilution curve of the shoot dry matter of direct-sowing winter oilseed rape was established. The NNI was calculated by using the model and plant shoot N concentration. The effects of N application rates on NNI at various stages were determined. The relationship between oilseed rape yield and NNI was investigated to determine the appropriate NNI in each period.【Result】Results showed that the N application significantly increased shoot dry matter and N concentration, and the difference between different N treatments was remarkable. The relationship between the shoot critical N concentration and shoot dry matter could be described by a power equation (N_cnc=3.49DM ^-0.26). This model could distinguish between N-limited and non-N limited group data from two independent experiments. The simulated N concentration was linearly correlated with the shoot actual N concentration, with the RMSE and n-RMSE of 0.37% and 13%, respectively, showing better stability of the model. The NNI increased as the N application rate increased within the range of the application rates in the study, and the response of NNI to N application rate was similar to the yield. The N application increased the seed yield significantly. Although there were differences in the response of N fertilizers to seed yield at varying experimental sites, the relative yield was closely related with the NNI of each experimental site. The NNI with the relative yield of 1 at the over-wintering, stem elongation and flowering stage were 1.35, 1.26 and 1.03, respectively. 【Conclusion】 The critical N concentration dilution curve N_cnc=3.49DM ^-0.26 was established, and the NNI could be used to evaluate plant N status and diagnose the N status of direct-sowing winter oilseed rape in Central China.