Abstract: Nowadays, the major issues facing crop husbandry in the arid oasis irrigation region are the sustainability of long-term continuous cropping of wheat and maize, the long period of fallow after the wheat harvest, and a comparatively low nitrogen (N) fertilizer use efficiency. Therefore, investigation of the effects of different green manure retention practices on nitrogen absorption and utilization of subsequent maize crops is of significant importance, and a field experiment was conducted in the Shiyang river basin to determine the effects of different green manure retention practices on nitrogen use characteristics of subsequent maize crops in a wheat-green manure-maize rotation system. Green manure retention practices evaluated were: i) Tillage with the total green manure crop incorporated into the soil, ii) No-tillage with the total green manure crop mulched on the soil surface, iii) Tillage with green manure crop roots incorporated in the soil and with above ground herbage removed; iv) No-tillage with above ground green manure crop herbage removed, and vi) Conventional tillage without green manure. It was found that before maize sowing, the treatments with the total green manure crop incorporated into the soil or mulched on the soil surface increased the soil mineral nitrogen content by 11.7% and 10.0%, respectively, and improved the microbial biomass nitrogen content by 14.3% and 16.2%, respectively, compared with conventional tillage without green manure. At the tasseling and silking stages, the two treatments increased soil mineral nitrogen content by 17.0% and 13.7%, respectively, and improved microbial biomass nitrogen content by 8.7% and 10.7%, respectively, in the 0-30 cm soil layer, which allowed efficient use of nitrogen by the maize. These two treatments also significantly increased above-ground nitrogen accumulation both in leaves and stems, and in the grain. As a result, the N use efficiency of these two treatments increased by 20.1% and 25.8%, respectively, and the N partial productivity by 17.3% and 22.2%, respectively, compared to conventional tillage without green manure. Furthermore, the N fertilizer use efficiency and nitrogen use efficiency of the two treatments were significantly higher than those for the treatment with green manure roots retuned only. In summary, in the arid oasis irrigation area, the practices of incorporating the total green manure crop into the soil or mulching the total crop on the soil surface using no-tillage, can increase soil nitrogen content while at the same time facilitating increased nitrogen use efficiency in maize.

Key words: green manure, retention practices, maize, nitrogen absorption and utilization