小麦-玉米轮作体系多年定位试验中作物氮肥利用率计算方法探讨

近年来,国内学者针对氮肥利用率的概念、内涵和计算方法进行了深入的思考与探讨,在提出质疑的同时也给出了一些改进的计算方法.本文结合5年试验数据,以小麦-玉米轮作体系多年定位试验为研究对象,初步探讨了这些改进方法在农田氮肥利用状况评价中的适用性.结果表明: 利用常规差减法分两季作物分别计算当季氮肥利用率时存在小区土壤肥力不均一的弊端,且计算值逐年增大,已不能很好地反映田间实际情况;将小麦 玉米轮作体系作为整体计算体系累计氮肥利用率,可以确保计算建立在小区土壤肥力均一的基础上,且计算值较低,变异较小;基于比值法计算的体系氮肥利用率较累计计算法数值偏大,年际间变异最小,数值最稳定;土壤氮素平衡法计算体系氮肥利用率时,考虑了土壤养分在作物种植前后的盈亏和环境养分的输入,计算值最大,年际间变异也最大.

Discussion on the calculation method of nitrogen use efficiency (NUE) in long-term field experiments under wheat and maize rotation systems.

In recent years, some scholars from China have deeply discussed about the concept, connotation and calculating method of nitrogen use efficiency (NUE), and have raised questions and also put forward some improved methods for NUE calculation in cultivated lands. In this paper, we compared advantages and disadvantages of these improved NUE calculation methods by using the data from a 5-year positioning field experiment under a wheat maize rotation system. The results indicated that it made mistakes when the traditional subtraction method was used to calculate NUE for wheat season and maize season separately, since the soil fertility level of experimental plots had differed significantly from each other after several seasons or years of different fertilization managements. Additionally, the calculated NUE increased markedly with the cropping season going, thus making it difficult to mirror the actual situation of N utilization in cultivated lands. For the wheat maize rotation system, the cumulative NUE calculation method considered wheat season and maize season as a whole part, and skillfully avoided mistakes which could be caused by inhomogeneity of soil fertility levels between experimental plots. Moreover, the calculated NUE were comparably smaller, with smaller coefficient variations (CVs), in contrast with the traditional subtraction method. The NUE calculated by using the ratio method were bigger, with the smallest CVs, than that computed by using the cumulative calculation method. The soil N balance method took a thoughtful consideration about the budgets and losses of soil nutrients before and after crop growth, but obtained the largest values of NUE and CVs within these methods.