【Objective】 The aim of this paper was to study the mechanisms of interspecific nitrogen facilitation and transfer in the relay-planting systems of wheat/maize/soybean and wheat/maize/sweet potato.

A root barrier pot experiment was employed to investigate the nitrogen uptake and utilization and interspecies reciprocity of "wheat/maize/soybean" and "wheat/maize/sweet potato".

By adopting the double optimal value method,the annual optimal amount of nitrogen fertilizer and the ratio of nitrogen fertilizer distributed among crops in the relay-planting system of "wheat/maize/soybean" were studied.

Effect of wheat/maize intercropping and nitrogen fertilizer on water use;

Effect of wheat/maize intercropping on plant nitrogen uptake and soil nitrate nitrogen concentration;

Effects of nitrogen fertilizer application and irrigationlevel on soil nitrate nitrogen accumulation and water and nitrogen use efficiency for wheat/maize intercropping

Intercropping advantage and contribution of above-ground and under-ground interactions in wheat-maize intercropping;

Methods We employed a micro-plot experiment and root barriers in a wheat-maize intercropping system with or without maize plastic sheet mulching.

hm~(-2)), wheat-maize intercropping soil NO3--N content and distribution with the increase in nitrogen application rate increased, and in different growth stages of different crops in different soil depth and bring a certain degree of regularity there.