Study On Nitrogen Release Characteristic And Biological Effect Of Modified Starch-coating-urea

Chemical fertilizers plays an important role in agricultural production, it is the biggest material investment in the agricultural, accounts for approximately 50% of all its productive spending. At present, utilization rate in current season of fertilizer in China is lower, the utilization rate in current season of nitrogen is 30%-35%, what of phosphorus is 10%-20%, what of potassium is 30%-35%. And the loss of nitrogen is very serious, it not only caused the direct economic losses, but also caused environmental pollution of part of areas because of incorrect fertilizing method. According to the study of statistics, in China, 45% of nitrogenous fertilizer has lost, and in some areas, the number can reach to 80-90%. How to play fully role of chemical fertilizer is one of the most prominent problems which will be solved by the modern agricultural sustainable development.Slow/controlled release fertilizer is made by a certain physical method, in this way, the fertilizer is wrapped by special materials, during the growth period or a cycle of the crop, the slow/controlled release fertilizer is applied only one time, then it can play fertilizer effect so gradually that the release of nutrient can be in accordance with crops, so as to improve yield, to enhance the quality, to reduce the loss of fertilizer and environmental pollution, and protect the environment.At present, what occupied the most of the coating materials of slow/controlled release fertilizer at home and abroad is composite organic polymer, its characteristics are that the thickness of the coating material is controllable and they are nearly not impacted by the soil condition, and the diffusion rate of nutrient can be controlled by the chemical character of polymer, so the controlled release can be realized. But, the price of this kind of material is very high, and it decomposes in the soil very slowly and can bring environmental pollution. What is more, the release of nutrient of this fertilizer coated by organic polymer can be impacted by the soil water, and it can meet the requirement of crop in the dry season. In our planting process, urea is the common fertilizer, the study adopted modified starch made by the method of socket skill copolymerization as the slow-release agent(the main material were corn flour, bentonite, lightweight magnesium carbonate), urea was wrapped by the different amount of slow release agent, and the modified starch-coating- slow-release-urea (FCU) was made, the nitrogen release characteristics and biological effect of FCU was studied through the simulation test and field test to provide theoretical basis and technical support for nutrient management of winter wheat and summer corn and for application of technology of slow release fertilizer.The water dissolution rate method and soil column leaching were used to study the nitrogen release; the pot experiment was used to study the biological effect and the impact on the absorption of nitrogen under the condition of drought stress, normal and excessive water, and the correlation analysis was used to identify the suitable evaluation method. The field application effect and environmental effect were also studied to identify the biological effectiveness and environmental friendly character. The main results are as follows:(1) The results from the water dissolution rate method and soil column leaching showed that compared with urea, the nitrogen release rate of the FCU was lower, it made a certain slow release performance. But, the releasing curve of the nitrogen had many differences with resin-coating-urea, this showed that the coating material had some effect on the nitrogen release. And, compared with resin, the water stability of the starch was not good, so it was not good to adopt the water dissolution rate method to evaluate FCU.(2) The results from the corn pot experiment at the seedling stage showed that under the condition of normal and excessive water, FCU made good slow-release performance whose chlorophyll content, dry matter weight, nitrogen uptake and NO₃- of the soil were all higher than the urea treat. Under the condition of drought stress, compared with resin-coating urea, it showed good drought-resistant and slow-release effect. So, FCU had not only the slow-release effect, but also some drought-resistant and moist-locking characteristics, it can be applied in the arid and semi-arid agricultural area widely.(3) Through the correlation analysis of the results of FCU from the soil column leaching method and pot experiment, we can see that the two methods had a significant correlation: under the condition of drought stress, the level of N1: Y_pot=13.481Y_soil-787.98,R²=0.9926; the level of N2: Y_pot=14.151Ysoi l-802.6,R²=0.9872. (Y_pot represented Nitrogen accumulation, mg/pot, Y_soil represented the releasing rate of Nitrogen accumulation, %). Soil column leaching method had the same condition with the pot experiment, and the results from the two methods tended to be consistent, so the soil column leaching method can be used to evaluate the characteristics of the coating fertilizer. Using soil column leaching method together with pot experiment can better reflect the actual slow-release characteristics of slow/controlled release fertilizer.(4) In the application of winter wheat, FCU can increase the effective tiller of winter wheat during the green returned stage, it can also improve the dry matter weight and root vigor, compared with urea, under the N150 level, the root vigor of FCU1 and FCU2 improved 7.04%-16.66%, under the N250 level, the increases were 4.9% and 16.29%.During the heading period of winter wheat, it improved the water use efficiency of flag leaf, the increases of the treats of N150 and N250 were 13.72%-25.17% and 8.63%-16.91%.It improved the dry matter weight and economic coefficient at the harvest stage.It improved the grain yield of winter wheat. During 2008-2009, the production of N150 treat and N250 treat increased 0.67%-25.51% and 14.7%-16.5%. during 2009-2010, N150 treat, the increase of yield of FCU1 was 1.94%; N250 treat, the increases of FCU1 and FCU2 were 2.81% and 0.28%.It improved the NO₃- content of 0 to 40cm soil during the green returned stage, this was helpful for later growth of plant. And, at the harvest-time, it can maintain much more NO₃- content in 0-40cm soil, and lower content in 40-100cm soil. This can not only ensure the fully fertilizer in the soil, but also can reduce the risk of nitrogen leaching loss, this can meet the characteristics of nutrient release of slow release fertilizer.It promoted the absorption of N, P, K, improved the nitrogen utilization of fertilizer. During 2008-2009, the increases of nitrogen utilizations of N150 treat and N250 treat were 25.48%-33.05% and 5.42%-22.22%. During 2009-2010, the increases were 10.57%- 16.32% and 1.19%-7.68%.(5) In the application of summer corn, under N150 level, it improved the dry matter weight at the harvest stage; under N250 level, it improved the economic coefficient.Under N150 level, the increase of yield of FCU2 was 0.16%; under N250 level, the increases of FCU1 and FCU2 were 10.76% and 7.72%.At the harvest stage, under N150 level, the NO₃- contents in 0-20cm soil of FCU1 and FCU2 were higher, and in 20-40cm, 40-70cm, 70-100cm soil, the NO₃- contents were lower; under N250 level, in 0-20cm soil, the NO₃- content of FCU2 was highest. In 20-40cm soil, the NO₃- contents of both FCU1 and FCU2 were higher than urea. In 40-70cm and 70-100cm soil, NO₃- contents of FCU1 and FCU2 were lower than urea.It promoted the absorption of N, P, K, improved the nitrogen utilization of fertilizer. the increase of nitrogen utilization of N150 treat was 12.46%; and the increases of FCU1 and FCU2 of N250 treat were 18.03% and 7.23%.Compared with urea, the nutrient of modified starch-coating-urea released smoothly, and the releasing period was longer, in previous it can controlled the release of nutrient effectively, this can avoid the loss caused by lower absorption in the previous and can solve the top dressing because of application of urea, and at the key period which needed lots of nutrient, it can maintain quick and stable release and can meet the demand of nutrient at the later stage, this can make sure of higher yield. But the yield of modified starch-coating-urea treat under the 150 kg N/hm² was not significantly different with what under the 250 kg N/hm² level, and under the 250 kg N/hm² level, the nitrogen utilization was lower, so, looking comprehensively, under this experiment condition, 250 kg N/hm² was advisable.