| In recent years, the rice grain yield has increasing with the large input of chemical fertilizers. However, many negative problems appeared, such as low fertilizer use efficiency, agricultural non-point source pollution, soil fertility unbalance, planting cost increase and benefit decrease. How to avoid or reduce the bad consquneces mentioned above, meanwhile remain the current rice yield level, is always the focus of current research. Paddy fertilization is region-specific, so the information obtained from one site could not be used to provide guidance for the farming in other site. Central Zhejiang area is a very important rice production area, and understanding the circumstance of fertilization of this area will benefit the rice farming.Excessive nitrogen fertilizer application is common in China. Although many studies on N fertilizer optimization have been conducted in other rice production regions, relevant studies were seldom done in central Zhejiang area.There are many studies concerning the effects of fertilization on rice yield, nutrient use efficiency, rice quality and soil fertility. However, most studies have been conducted within a short period of time and can provide only preliminary fertilizer recommendations, which need further calibration through multi-year field experiments. Long-term field experiments (LTFEs), which are records of the past and may serve as early warning systems for the future, are crucially important for understanding changes in crop yields, estimating nutrient dynamics and balances and assessing system sustainability that cannot be revealed in short-term studies. Some LTFEs are carried out to monitor the effects of fertilization on soil quality, fertility, and productivity under various types of soil and cropping systems. However, little detailed information is available on rice yield response to long-term fertilization and soil fertility changes in single rice cropping system in central Zhejiang area and other places of China.In this paper, we studied the effects of various nitrogen rates on rice(Oryza sativa L.) yield, nitrogen use efficiency and quality of paddy field water; the effects of different nitrogen, phosphorus and potassium treatments on rice yield, nutrient absorption-utilization and economic benefit; the effects of different nitrogen, phosphorus and potassium treatments on soil fertility and rice quality; study and demonstration of slow-controlled release compound fertilizer in paddy field. The main results are summarized as follows:1. Results of the effects of various N rates on rice (Oryza sativa L.) yield, N use efficiency (NUE) and quality of paddy field water showed that no significant yield differences were observed under N rates from 180 to 315 kg/hm2. Nitrogen use efficiency (REN, AEN and PFPN) could be improved by reducing N application rates without significantly decreasing yield. NH4+-N is the main form in surface water, and 5-7 days after N application was a critical stage for reducing N pollution. NO3--N is the main form in percolation water, and there is little adverse impact on the underground water due to its low concentration. Deduced from the "lineage+platform" equation, the N rate for the highest yield was 176 kg/hm2 accounting for 65% of the conventional N rate (270 kg/hm2).2. Results of the effects of different nitrogen (N), phosphorus (P) and potassium (K) treatments on rice yield, nutrient absorption-utilization and economic benefit (2008-2013) confirmed that N, P and K fertilization significantly increased rice grain yield, and the effect of combination of these three fertilizers on grain yield was better than any of two fertilizers combination; the yield-increasing effect was in the order N>K>P. The highest yield appeared in N3P2K2 treatment, which was 8900 kg/hm2. The rice total nutrient (N, P2O5, K2O) accumulation and nutrient absorption rates per 100 kg seed increased with the increase of applied fertilizer rates, while the nutrient recovery efficiency and agronomic efficiency decreased with the increase of applied fertilizer rates. The recovery efficiency for N, P and K were 25.2%,38.3% and 36.0%, respectively. The economic benefits significantly increased by 21.1%,20.3%,20.3% and 22.4% for N2P2K2, N2P3K2, N2P2K1 and N3P2K2 treatments, respectively, compared with N0P0K0 treatment. Deduced from the fertilizer effect equations, the P2O5 and K2O application rates for the highest grain yield were 39.3 kg/hm2 and 100.8 kg/hm2, respectively.3. Results of the effects of different nitrogen (N), phosphorus (P) and potassium (K) treatments on soil fertility and rice quality (2008-2013) showed that fertilization had no impact on soil pH. Soil fallow was benefitial for the increase of soil organic matter content. Averagely, soil organic matter content for all treatments increased by 14% compared with the initial value. Soil total nitrogen content increased by 9.6% averagely compared with the initial value. Soil available phosphorus and potassium contents decreased significantly under current P and K application rates, so the "2" level should be increased considering the maintenance of soil fertility. N fertilization improved gel consistency (GC), protein content (PC) and total amino acid content, meanwhile reduced alkali spreading value (ASV); P fertilization improved PC; K fertilization improved GC, ASV and PC.4. For slow-controlled release compound fertilizer 100% treatment (SCRCF100%), rice yield increased by 6.2%, rice chalkness degree and alkali spreading value decreased by 8.6% and 2.4%, and economic benefit increased by 7.5%, compared with the traditional compound fertilizer treatment (TCF). When the rate of SCRCF was reduced by 20% (SCRCF80%), the yield showed a decrease trend, but there was no significant difference in yield between SCRCF80% and TCF. Result confirmed that SCRCF 100% made the best performance among all treatments, namely, when the application rate is 775 kg/hm2 for slow-controlled release compound fertilizer (20-10-18), the optimum benefit will be obtained.5. Using the data and experience from the "3414" experiment, we popularized and demonstrated two kinds of slow-controlled release compound fertilizer (20-10-18) and (23-11-12) in paddy field. Results showed that the grain yield increased by 5%, economic income increased by 1050 yuan/hm2, and labor cost saved by 150 yuan/hm2. |
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