基于土壤氮素平衡的氮肥推荐方法——以水稻为例

SOIL NITROGEN BALANCE BASED RECOMMENDATION OF NITROGEN FERTILIZATION: A CASE STUDY OF RICE

基于土壤氮素平衡提出了一种新的氮肥推荐方法——氮素归还指数法,并以水稻为例介绍了其实施过程。经江苏省太湖地区和里下河地区45个水稻田块的举例推荐,用肥料效应函数法推荐的最佳经济施氮量(OENR)、氮素归还指数法推荐的氮素归还施氮量(RNR)和理论施氮量法推荐的理论施氮量(TNR)分别平均为N 246.8±42.5、216.9±27.3和176.9±22.3 kg hm-2。氮素归还指数法可不经过田间试验实现以目标产量为唯一变量的氮肥推荐,但在区域氮素净损失率能否保持相对稳定、长期实施氮素归还施氮量能否使土壤不致产生氮素盈余等方面仍需进一步研究。

Based on nitrogen （N） balance in soil system, a new N fertilization recommendation method, i.e. ＂ N return index （NRI）＂ method, was introduced. The NRI concept was brought forth by the Nutrient Return Doctrines, and means how much N must be returned to soil in order to maintain soil N balance when one kilogram N is taken off by crop harvesting. On the assumption that other than N fertilization, the N inflow via atmosphere deposition, irrigation and seeding （ N biofixation and N in straw incorporation exclusive） and the N outflow via erosion, runoff, leaching, volatilization, and nitrification-denitrification, are constant, an equation for calculation of NRI （ NRI = 1 - △E/FN ） was deduced, where AE stands for increase in N output from soil to environment induced by N application; FN for N input with fertilizer applied, and △E/FN is net N loss. With the target yield （ Y, ） of the fields most farmers are familiar with set as the only vari- able to distinguish fields different in soil fertility, an equation for NRI-based recommendation of N fertilization was worked out, i.e. RNR = RNRI × N100 × Y1/100＂ , where RNR stands for recycled N rate, RNRI for the regional NRI, which is a relatively stable constant in a specific farming area, N100 for N uptake by one hundred kilogram grains, which is in a significant linear relationship with crop yield. By taking into account the actual production practices, the equation was finally amended as ＂ RNR = RNRI × N100× Y1/100 - WN＂ , where WN stands for N input via biofixation and straw incorporation. To verily effectiveness of NRI, two regions in Lixiahe Plain and Taihu Lake Basin in Jiangsu Province were selected as for the study. Based on the soil N budgeting data of the study areas during the rice growing season, RNRI was worked out to be 1.52, based on traits of rice cultivars, N100Was 8.67 × 10^-5Y1 ＋ 1. 161 （r =0. 828 0＊＊ ） and based on N biofization and straw incorporation, WN was N 52.3 kg hm^-2, then the equation of ＂RNR = 1.32 ×10^-6Y1 ＋ 1.76 ×10^- 2Y1- 52.3＂ for recommendation of N fertilization for rice in the study areas was figured out. Based on the data of the fertilization experiment on 45 cuhivars of japonica rice in recent years, comparison was performed between N fertilization recom- mendations using different methods, the fertilizer effective function （FEF） , NRI and theoretical N rate （TNR） in effec- tiveness. Results show that the optimal economic N application rate （OENR） recommended by FEF, the N-recycling N application rate （RNR） by NRI and the theoretic N application rate （TNR） by TNR was N 246.8 ± 42.5 kg hm^-2, 216.9 ±27.3 kg hm 2and 176.9 ±22.3 kg hm^-2 respectively. Compared with OENR, RNR was 2.4% less in rice grain yield and 500 yuan hm 2 in economic benefits, but saved N 29.9 kg hm^-2and 10.3 kg hm^-2, respectively, from N application and soil-N net loss and moreover kept soil-N in a rough balance. The new method can be used to make recommendation for N fertilization with target yield being the only variable and without the need to go through field experiment, however, further study is still required to see whether RNRI will remain relatively stable for long, and whether long-term use of the method would lead to soil-N surplus or not.