Study On Nitrogen Release Characteristics And The Utilization Efficiency Of Rice Controlled Release Fertilizers In Paddy Fields

A large amount of nitrogen fertilizer was used in rice-growing areas of southern China. Because nitrogen recovery of nitrogen fertilizer was very low, The crop output per unit nitrogen application decreased and the environment was polluted seriously. Water culture experiments in laboratory, field experiments and laboratory model tests were carried out to study nitrogen release characteristics of the rice controlled release fertilizer under the conditions of field and water culture; its nitrogen fate in agro-ecosystem; synchronization between N release rates from rice controlled release fertilizer and N uptake rate by rice in different growth stages; effect of different application rate of controlled release fertilizer on nitrogen utilization and rice yield; yield increase efficiency and nutrient utilization of rice controlled release nitrogen fertilizer in different soil fertility level. The main results were showed as following:1. In water of 25℃, it takes 50 and 70 days after applying them that 80% of N was released from early rice controlled release fertilizer and late rice controlled release fertilizer, respectively. The N absorption patterns of early rice controlled release fertilizer from early rice and of late rice from late rice controlled release fertilizer both were expressed by exponential equation and described as a function of temperature. Its formula was N=N0[1梕xp (-kt) ]. In water at 15?5℃,the rate of nitrogen release from rice controlled fertilizer was increased as temperature increased. When the temperature increased by 10"C, the rate of nitrogen release from rice controlled fertilizer was increased by 1.8 ?2.0 times. In field condition on taking the days after fertilizer application and cumulative soil temperature as the variable, CNR can be described by the formulas CNR=a+bD+cD2 and CNR=a+b (CST)+c (CST) 2 , respectively.2. The results of I5N labeling experiment showed that NH3 volatilization losses of urea and rice controlled release nitrogen fertilizer in 11 days after fertilizer application accounted for 1.81% and 0. 69% of applied N, respectively. The amount of NH, volatilization loss reached a maximum valuein the five days after nitrogen application, thereafter, it was decreased gradually. Leaching losses of nitrogen from urea and rice controlled release fertilizer only amounted to 1.02 % and 0.95% of applied N, respectively. The leaching loss of N from rice controlled release fertilizer changed smoothly during the whole growth period of rice plant, and only increased a little until 40 days after fertilizer application, thereafter, it decreased slowly again. Nitrification-denitrification loss of rice controlled release fertilizer was 3.46%, but that of urea was as high as 37.75%. Residual fertilizer nitrogen mainly remained in the soil layer of 0-35cm depths and reached 91.4%-91.5%. There was only trace amount of residual nitrogen under the soil layer of 35cm depth. The total residual nitrogen of rice controlled release fertilizer in soils was slightly more than that of urea. Nitrogen recovery of rice controlled release fertilizer treatment was 73.8% and was higher 34.9% than that of urea. The high N recovery of rice controlled release nitrogen fertilizer may be explained by the following reasons: (l)nitrogen release in its granulated fertilizer was controlled; (2) there was lower leaching nitrogen and lower Nlla volatilization, especially smaller nitrification-denitrification loss.3. Controlled-release fertilizers are more desirable if release characteristics are synchronized to plant uptake. This study was conducted to determine the relationship between N release from controlled release fertilizer and N uptake by rice plants under paddy field. N release rate of controlled release fertilizer was high at the early growth stages, but gradually decreased with time. The cumulative N release reached about 80% of the total N content of fertilizer at around 70 day after application or when cumulative air temperature had reached about 2000癈. Nitrogen uptake from the fertil...