Availability Of Phosphorus Of Controlled-Release Fertilizers In Calcareous Soil And Their Effects On Growth Of Soybean

Studies showed that nutrients of controlled release fertilizers (CRFS) were in accordance with the absorption of plants, thus increasing the fertilizer use efficiency, promoting the burgeoning and growth of plants, and enhancing the yields of fruits. Most studies concentrated on the research of nitrogen (N), in contrast, less researches were done on the phosphorous (P) in CRFS. However, despite the slow release rate of P in CRFS, the feasibility of whether the P in CRFS can satisfy the demand of plants for nutrients needing further researching. The CRFS utilized in the experiments in contrast with the common P fertilizers were produced in Shandong agricultural university. This research was conducted to study release rate of P in CRFS in soil and the effects of dynamic changes of nutrients on the growth of plants. Besides, the capacity of adsorption and separation in typical calcareous soil was also researched. All the experiments were intended to provide the theoretical support for the exploration and improvement of new type of CRFS. And the main results were as follows:1. Effects of CRDA on the growth of soybeans: with the same amount of N and K, the diameters of stalks, content of chlorophyll, and the content of total P in leaves and stems with treatment CRDA2 were superior to that of common compound fertilizers. In addition, the application of CRDA can significantly promote the yields of soybeans, and the outputs of soybeans treatment CRDA2 increased by 30.45%and 13.15%comparing with control and treatment CDA2 respectively.2. Effects of P released in aftereffect experiments of CRFS on the growth of Coles: with the same amount of fertilizers, the number of leaves in the treatments CRF1 and CRF2 were 1.2 and 0.9 times than that of treatment CCF; and content of chlorophyll and leaf areas in treatment CRF2 were significantly greater than that of treatment CCF2.The nutrients in the soil solutes can give a precise and timely indication of nutrient characteristics of soil. In the initial period of growth, treatment CRF1 and CRF2 had greater content of P in soil solutes than that of CCF. With the application of same amount of fertilizers, the dry weight of both stem and leaves increased by 139% and 204% comparing with treatment CCF and control respectively. The results showed that the aftereffect experiments of CRFS was significantly better than CCF, and can promote the growth and dry weight of both stems and leaves.3. Effects of coated CRFS on the available P: the dynamic change of available P in soil can reflect the release rate of CRFS. Comparing with CCF, the P in CRFS can release slowly and reach the summit during legumes periods, in good consistency with the demand of nutrient, which can promote the growth of soybeans and increase the nutrient use efficiency.4.Effects of P in CRFS on the appreciation index and yields of soybeans: with the same amount of fertilizers, the number of leaves,content of chlorophyll and number of legumes in the treatments CRF was significantly greater than that of treatment CCF.With the same amount of fertilizers, the yields of beans in the treatments CRF1,CRF2 and CRF3 increased by 50.45%,32.68% and 25.06% respectively comparing with that of treatment CCF. With the application of same amount of P and K, the outputs of beans with treatment CCFS was on the steady increase. In comparison, the outputs reach its maximum with the treatment CRF1. Comparing with CCF3 (with highest P content),the legumes, numbers of soybeans and outputs with the treatment CRF1(with lowest P content) increased by 14.77%,26.41% and 25.86%.In conclusion, with the one third amount of CCF, the CRFS received higher yields. Not only can application of CRDA save much P resources, but can receive economical benefits. 5. Effects of different grads of concentrations on adsorption and desorption isotherm of the P at the same temperature in the soil in farmland, orchard soil and vegetable soil. With the same grads of low P concentration, the farmland soil obtained the maximum amount adsorbed. At the P concentration of 400mg/L, orchard soil received maximum amount adsorbed and the capacity of adsorption is: soil in farmland >orchard soil>garden soil. K value in some sense indicated the capacity of P adsorption, and farmland soil had the largest K value, thus possessing the greatest capacity of adsorption. Besides, the order of MBC value is: soil in farmland > orchard soil> garden soil.While the grads of P concentration were less than 200mgP/L, the difference of separation amount was not significant. And at the P concentration of 400 mg P/L and 800 mg P/L, the amount desorbed of garden soil is significantly higher than that of soil in farmland and orchard soil.