Effects of slow-released nitrogen fertilizers with different application patterns on crop yields and nitrogen fertilizer use efficiency in rice-wheat rotation system

【Objectives】Rice-wheat rotation is one of the most important agricultural cultivation systems in China where large amounts of fertilizer are applied. Yield increases of rice and wheat, decrease of fertilizer application amount, and increase of fertilizer use efficiency can benefit from research on application patterns and methods of various fertilizers in such rice-wheat rotation regions. Slow-released fertilizers as nutrient-efficient and environment-friendly fertilizers have been extensively reported to function in increasing yields and fertilizer use efficiencies in various crop species. However, less attention is paid to effects of slow-released fertilizers in crop rotation system, especially rice-wheat rotation system which is the most important rotation system in southern China. 【Methods】Here, the effects of different slow-released fertilizers on the yields of rice and wheat, the use efficiency of nitrogen fertilizer, the contents of soil nutrients, and the soil nitrogen balance were studied through a two-year field plot experiment of the rice-wheat rotation. There were six experimental treatments including no nitrogen, custom fertilizer, slow-release fertilizer Ⅰ (20% common urea + 80% sulfur coated urea), slow-release fertilizer Ⅱ (20% common urea + 80% polymer coated urea), slow-release fertilizer Ⅲ (common urea + 0.8% NAM) and slow-release fertilizer Ⅳ (common urea + 0.8% NAM). Among them, the nitrogen application amounts of the slow-release fertilizer Ⅰ, slow-release fertilizer Ⅱ and slow-release fertilizer Ⅲ were reduced by 24.3%, and the nitrogen application amount of slow-release fertilizer Ⅳ was reduced by 10.8%. 【Results】Compared with the no nitrogen application, all treatments with the nitrogen application increase the yields of wheat and rice in every year. Among these treatments, the custom fertilizer shows the highest yield increases. The effects of the fertilizer are more significant on wheat than on rice and in the second year than in the first year. Compared with the accustomed fertilization application, the decreases of the N application by 24.3% or 10.8% do not decrease wheat yields in two seasons for all investigated slow-released fertilizers, and the reductions of the nitrogen application by 24.3% using polymer coated urea and by 10.8% using common urea + NAM also do not decrease rice yields in two seasons. However, when the N application of slow-released fertilizers is reduced by 24.3%, the rice yields are decreased in the second season using the common urea + NAM, and in two seasons using the sulfur coated urea. The nitrogen fertilizer use efficiencies of all investigated slow-released fertilizers are higher than those of the accustomed fertilization application, and at the same time, there is less soil remaining nitrogen in the all treatments of the slow-release fertilizers compared with the accustomed fertilization application. Among 4 slow-release fertilizers, the slow-release fertilizer Ⅲ shows higher nitrogen fertilizer use efficiency and less soil remaining nitrogen, indicating its potential in the rice-wheat rotation system for increasing nitrogen use efficiency and decreasing nitrogen loss. No obvious change patterns are found in the effects of different slow-released fertilizers on soil nutrient contents.【Conclusions】These results suggest that, in the present condition of the rice-wheat rotation system, the slow-released fertilizers exhibit better effects on wheat than on rice, as the reduction of N application amount for some slow-released fertilizers decreases rice yields. Thus, it seems necessary to research and develop the specific slow-released fertilizers suitable for rice.