The Effect Of Irrigation Patterns And Nitrogen Levels On Rice Nitrogen Use Efficiency And On Nitrogen Supply Capability And Leaching Risk In Paddy Soil

Water and nitrogen are the most important and active soil fertility factors on rice growth and the most adjustable and controllable environmental factors in paddy ecosystem. It is true that the nitrogen fertilizer recovery efficiency coulde be increased and the rice production cost and nitrogen lossing risk coulde be reduced if the synergy interation between the nutritional factors and the environmental factors coulde be brought into played. For this reason, a two-year pot experiment with rice-wheat rotation system was conducted to investigate the effects of irrigation patterns and nitrogen (N) fertilizer levels on the N use efficiency of rice, the N supply capability and N leaching risk in paddy soil. The experiment was designed with four N fertilizer rates of NO, N1, N2, and N3 (i.e.,0 N kg·hm-2,126 N kg-hm-2,157.5 N kg·hm-2, and 210 N kg-hm"2, respectively) and two irrigation patterns of FW (continuous water-logging irrigation) and CW (water-controlled irrigation). The rice varietyⅡYou 838 and alluvial soils from Hubei province were used in this experiment. The results are showed as follows.(1) The grain yield, aerial part biomass, N accumulation and N use efficiency of rice were significantly affected by water management patterns and the N fertilizer levels.While the higher effects were observed in N fertilizer levels compared with water management patterns. Although the aerial part biomass and N accumulationof rice were increased as N fertilizer level enhanced, the nitrogen agronomic efficiency, nitrogen recovery efficiency, partial factor productivity and nitrogen physiological efficiency were decreased as N fertilizer level increased. There were no significant differences revealed between the two higher N fertilizer levels of N2 and N3.(2) The dynamic trends of the soil NO3--N and NH4+-N contents extracted by ion exchange resin were studied under different irrigation patterns and nitrogen levels during rice growing season. Results showed that the contents of resin extractable NO3--N and NH4+-N decreased as the rice growing period passed. Which implied that amount of available N in soil for rice root uptaking was sharply decreased at late growing stages. More than 50% of resin extractable N in soil were NO3--N under each experimental treatment, during every rice growth period except to the fourth week after transplanting, which indicated that the primary formation of N supplied by soil was NO3--N. The contents of resin extractable NO3--N and NH4+-N in soil were noticeably affected by nitrogen fertilizer level during 2 weeks after N fertilizer applied. Higher NO3--N contents were detected under water-controlled irrigation mode in comparison with continuous water-logging irrigation.(3) The concentration of total N (TN) in soil leachate decreased gradually as the rice growing season passed. N leaching loss risk mainly appeared within 40 days after rice transplanting.The primary forms of N in soil leachate were NO3--N and soluble organic nitrogen (SON). The content of NH4+-N in soil leachate was relatively lower compared to NO3--N and SON. The concentration of NO3--N in soil leachate reached the highest level from the 20th day to the 30th day after rice transplanting and were significantly increased as the N level enhanced during this period. In contrast to N3 (local recommendation N dosage), the N2 treatment (75% of N3) appeared higher nitrogen use efficiency (NUE) and lower N loss risk under the both two irrigation patterns。...