农田水氮关系及其协同管理

作物施氮反应及其氮肥利用率不仅取决于氮肥管理，还与水资源管理有关，并且受到地区气候因素的影响。针对中国灌溉农区氮肥环境污染问题日益突出，协调农田水氮管理，如通过改善水资源管理，发挥水氮协同效应，以提高水分利用效率来改善氮肥利用率，实现水氮利用率双赢，是当前农业水氮管理中亟待探讨和回答的问题。通过对农田水氮协同相关研究文献资料的综述，以华北平原集约种植体系水氮管理为例，根据历年统计数据，分析了该区年水热条件下粮食产量与水、氮及水氮利用效率之间的关系。研究表明，水和氮与作物产量在一定范围表现为水氮的协同效应。水分利用效率一般随灌溉水量减少及氮肥用量增加而提高；氮肥利用效率随氮用量增加而下降。适量节水和减氮分别有助水分利用效率和氮肥利用效率的改善。在气候变暖、变干条件下，适量施氮成为改善水氮利用效率的关键对策。

Opinions on water-nitrogen relations and their synergic management

Crop response to nitrogen (N) fertilization and N use efficiency (NUE) depend not only on N management, but also on water resource management and local climate. To the increasing environmental pollution induced by over-use of N in the irrigated areas, regulation of water-N management for achieving a win-win situation that will improve water use efficiency (WUE) and NUE has been still very concerned. Through literature reviews concerning water-N relations and their synergic management, as well as statistic data analysis with emphasis on an intensive wheat-maize cropping system in the North China Plain, the relationships between grain yields, water and N, as well as their use efficiencies under the regional climate conditions have been discussed. In the last 20 years, the research on water-N management in China has been involved in rainfed farming areas, and further in water-saving irrigated farming areas. The recent research focused mainly and continuously on the improvement of crop yields and WUE in dryland farming, and also on N-related environmental problems associated with N over-use in the irrigated areas. Currently, in the intensive double-crop (wheat and maize) rotation systems in the North China Plain, a large amount of N surplus in soils and low response of crop yields to N fertilization in the most crop fields have been continuously exposed with annually over-N fertilizer inputs (as reported above 500-600 kg?hm-2?a-1). The low response of crop yields to irrigation water in some crop fields has been also observed due to over-irrigation. This implies that there is still a big scope for improvement of WUE and NUE by using water-saving and N-reducing practices in the irrigated areas. For instance, with recommended fertilization practices the NUE by wheat and maize could be up to 50% and 34%, respectively, as compared those with conventional practices (14% and 20%, respectively). According to China statistics (1988-2007) in the regions of North China Plain, the changes in grain yields per ha showed significantly positive correlations with the mean air temperature annually, but little with the variations in rainfall. With the trend of declining annual rainfall and increasing annual air temperature, the Precipitation use efficiency (PUE) increased but NUE decreased significantly. Based on many previous studies on water-N relation, the synergic relations between water, nitrogen, and crop yields were found in a given range. The WUE generally increased with decreasing irrigation water or increasing N fertilizer amount, while NUE declined with increasing the amount of N fertilizer. The WUE and NUE can be improved by using water-saving and N-reducing practices, respectively. Limited irrigation combined with the proper amount of N fertilizer will be a viable alternative to the condition of climate warming, and drying. As reviewed on water-N research progress abroad, some disparities between China and advanced counties exist, thus, further researches especially in the aspects of field or regional simulations, predictions, real-time monitoring and plant diagnosis related to crop water-N synergic management are still needed.