N And S Transformation Characteristics Of US In Soils And Its Crop Effect

Urea, as a nitrogen fertilizer, has been applied widely in agricultural product, but its drawbacks, such as the short fertilizer-efficiency, the low utilization-rate and as a sequence resulting to enviornmental pollution have attracted much more attention. Sulphur is one of the essential elements for plant growth, however, its decreasing application, and even not, to agriculture has led to unbalance between nitrogen and sulphur nutrition, and even to deficiency of sulphur in some areas, which almost up to 30% cultivate lands in China. US is a new type of fertilizer which both N and S essential elements, and made up by coating sulphur onto urea with advanced processing skills.The paper focuses on the study of N and S transformation process of US in soils and in crops by the experiments of ammonia volatilization, soil column leaching, pot-leaching with pakchoi, soil incubation and plant pot-cultivating experiment. The main results are as following:1. US could decrease the volatilization rate of ammonia and thus reduce the volatilization amounts. The peak period was later than common urea treatment. It indicated that US has good function of slowing release.2. The soil column leaching experiment showed that application of US could reduce leaching of NO3--N, U-N and P, enhance transformation of U-N to NH4+-N, and increase recovery of U-N, soil N as well, compared to urea at the same N level.3. Pot-leaching with pakchoi experiment showed that applying US resulted in more significant reduction of N-leaching and P-leaching than those of other treatments during the whole leaching period. US also increased efficiency of N compared to urea.4. The transformation of urea in soil depended on soil pH, urease activity and the nitrification effect. Applying US reduced soli pH. Elemental sulphur would produce urease and nitrification inhibitors when oxidation in soil. This would increase NH4+-N, U-N and reduce NO3--N content.5. Soil pH is an important factor influencing the transform of elemental sulfur. The pH value would become higher when application of US to soil than that of elemental sulphur. Thus application of US was helpful to oxidation sulphur and to increase of available S in soil. 6. Simultaneous application of N and S was useful for plant growth. The soil treated with US could promote the growth of pakchoi and peanut, and thus enhanced their yield.7. Application of US could significantly increase pakchoi and peanut plants uptake to nitrogen and sulphur at various growth stages, and enhance nitrogen and sulphur content, decrease the ratio of nitrogen to sulphur.8. Application of US increased the Vc content in pakchoi, the protein and rough fat content in peanut. The US reduced pakchoi nitrate content compared with urea.9. Application of US increased efficieney of N. N efficiency rate in pakchoi was 30.3%, 30.2% respectively, while in peanut was 59.6%, 62.0% respectively. Both treatments were higher than that with the urea significantly.10. Application of US decreased volatilization rate of ammoina and leaching loss of N and P, as well as increased fertilizer efficiency. That indicated US has a great environmental effect.