Zhou Jianbin 1,2, Liang Bin 1,2, Zhao Wei 1,2, Yang Xueyun 1,2
1 .College of Resources and Environmental Sciences, Northwest A&F University;
2. Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China,
 Ministry of Agriculture

As an essential nutrient, nitrogen (N) is generally of limiting availability to plants in terrestrial ecosystems. And N fertilizer is the wide used fertilizer in the world. It has contributed a lot to food security in the world, and also caused a series of problems, including eutrophication, greenhouse gas emission, and biodiversity diminishing. Better management of N in soil and plant system to synchronize N supply and crop demand is key to optimize the tradeoffs amongst yield, profit, and environmental protection. We hypothesized that the soil with high organic matter and microbial activities due to the long-term application of manure and chemical fertilizers could improve the synchrony between N supply and crop demand.
Micro-plot (PVC cylinders 24.5 cm in diameter and 63 cm long) experiment was settled in three long-term fertilized soils (Control, no fertilizer; NPK, added inorganic fertilizers including N, P, and K; and MNPK, combined application of manure and inorganic NPK fertilizer) of a 19-year field trial located in Yangling, Shaanxi to investigate the effects of incorporation of 15N fertilizer on changes of different forms of N in soil, wheat yields, N use efficiency, and N leaching in the different fertilized soils.
The control soil with very low fertility had the highest N leaching after crop harvest due to the less N uptake by crop and immobilization by soil microbes; and the use efficiency of the added N in this soil was only 20%, more than 30% of the added N was leached into 20-60 cm soil layer after harvesting wheat. Balancing fertilization (NPK and MNPK soils) increased the N uptake by crop and immobilized by microbes in soil, and significantly decrease the leaching of N fertilizer after wheat harvesting. The use efficiency of added N in these soils was as high as 60% to 65%. The MNPK soil immobilized higher proportion of the added N (14.1%) than NPK soil (12.6%) in the early growth stage of wheat; and 82% of the immobilized N in this soil was released from shooting to flowering stage. Our findings highlight that the important role of long-term application of manure plus NPK fertilizers in modulating N retention and supply in soil to increase N use efficiency and grain yield while minimizing N loss from soil.
Acknowledgements Project (No. 40773057, 40571087) supported by the National Natural Science Foundation of China.