Effects Of Irrigation, Nitrogen And Zeolite Management On Grain Yield, Water And Nitrogen Utilization In Paddy Field In Coastal China

Water shortages, over-fertilization and nitrogen non-point source pollution are now seriously threatening the sustainability of conventionally flooded rice production and food security. To reduce water resources and fertilizer consumption, and ensure food security with minimal associated environmental costs is the main task facing humanity today and a huge challenge for all scientists. Energy controlled irrigation and zeolite amendment were applied into rice production system for reducing water resources through energy controlled irrigation, and for improving soil water condition and fertilizer preservation within paddy subsurface soil through zeolite amendment, which optimized water-nitrogen coupling, and took advantages of incentive mechanism and synergy in water-fertilizer-soil system. ensuring low water and nitrogen consumptions, low nitrogen non-point source pollution and high yield. A field experiment using split-split plot design was conducted firstly in this study to determine the effects of nitrogen managements and zeolite amendment on soil physicochemical properties, rice growth, dry matter accumulation, nitrogen uptake, grain yield, and nitrogen utilization; develop simple nitrogen-zeolite rice production model; and clarify zeolite regulation mechanism about increasing grain yield, nitrogen absorption and nitrogen utilization. Meanwhile, a non-weighting lysimeter hierarchical experiment using a split-split-split plot design was conducted in 2012 and 2013 to study the effects of year, irrigation, nitrogen management, and zeolite amendment and their interactions on rice production, soil residual nitrogen, water and nitrogen utilization and use efficiencies, as well as incentive mechanism and synergy in water-fertilizer-soil system in response to zeolite amendment. Thereafter, the optimal rice production systems were determined through cost-benefit analysis from the perspective of resource consumption and the rice quality performance and the feasibility under the suggested rice production systems was evaluated including milling, appearance, cooking, nutritional and eating quality traits. It was concluded that:a) Zeolite addition to conventional paddy rice field significantly enhanced the cation exchange capacity ?CEC? of the upper 30 cm soil.Compared with paddy field without Z amendment,20.6-70.0% higher potential post-harvest residual soil mineral nitrogen and 9.7-30.7% higher exchangeable potassium was increased when the upper 30 cm profile soil amended with 5-15 t ha^-1 Z. Similarly, the total dry matter accumulation, total nitrogen extraction, and nitrogen fertilizer apparent recovery utilization ?NRE? and agronomic efficiencies ?NAE? were all significantly increased. However, the effects on organic matter and total nitrogen of the soil were not significant. The cause of zeolite amendment to increase yield is that zeolite significantly increases effective panicle number and the increased effective panicle number is due to increasing rate of zeolite amendment slow down the decline process of rice tiller dynamic curve, hence, reducing the ineffective tillers. Nitrogen application technology in combination with zeolite amendment can be equivalent to slow-release fertilizer, prolonging fertilizer availability and significantly increasing NRE and NAE.b) Zeolite addition to conventional paddy rice field significantly increased soil water content, water holding capacity and water retention capacity of the soil. At the soil matrix potential of -20 kPa, soil application of 5-15 t ha^-1 rate of Z resulted in 3.0%-6.1% higher volumetric soil water content than zero Z treatment. Addition rate of 5,10 and 15 t Z ha^-1 in paddy field reduced total irrigation water use by 4.3%,8.7% and 9.7%, and water use efficiency ?WUE? increased by 8.5%,23.9% and 29.6%. Considerable potential of water saving of zeolite is that increasing rate of Z amendment increased water holding capacity of soil, thus, improved paddy soil moisture status in the paddy field.c) Application of energy controlled irrigation to paddy fields reduced irrigation water by 28.4%, increased WUE by 56.6% and rice production by 11.5%. The water saving potential of energy controlled irrigation was mainly reflected in the tillering stage, booting stage and milking stage. Compared with conventional continuous flooding irrigation, rice evapotranspiration decreased by 64.8%,26.2% and 15.4% respectively. Energy controlled irrigation had a significant effect on increasing yield under three low nitrogen levels, but it was not obvious under the highest rate. In addition, higher nitrogen application resulted in a large reduction in NRE.d) Energy controlled irrigation amended with zeolite, not only inherited the advantages of saving water and increasing yield, but also buffered stress damage to crops, and further enhanced WUE based on energy controlled irrigation. Addition rate of 5,10 and 15 t Z ha^-1 in paddy field achieved 4.3%-20.1% higher NUE under CF irrigation and a much higher NUE ?12.9%-36.9%? under EC irrigation. The significant improvement of WUE is that the addition of zeolite increases the soil water holding capacity, reduces the water stress, providing a better nutritional environment for rice growth, and consequently increases NUE.e) N application in combination with energy controlled irrigation and zeolite amendment prevented decreases in grain yield and available N in plowing layer at higher N application rates under energy controlled irrigation. Cost-benefit analysis indicated the treatment of I_ECN₁₀₅Z₁₀ (105 kg·ha^-1 N application in combination with 10 t Z ha^-1 zeolite and energy controlled irrigation) achieved the highest profit,30,764 RMB ha^-1. The I_ECN₁₀₅Z₁₀ treatment reduced water and nitrogen use by 27.8% and 33.3%, respectively, and increased grain yield ?10.6%?, grain nitrogen accumulation ?3.5%?, residual nitrogen in the upper 30 cms of soil ?46.2%?, WUE ?52.5%?, NAE ?89.2%? and NRE ?54.5%?. Moreover, the positive effects of Z application last for at least two years, with one reference stating the effect lasts 7-20 years. If implementation of energy-controlled irrigation is prevented by the concomitant increase in labor costs required for its use, conventional flood irrigation can be used with 105 kg N and 5t Z ha^-1, thereby reducing nitrogen use by 33% while maintaining normal yields.f) Recommended treatement did not significantly affect quality traits. Energy controlled irrigation slightly decreased whole grain milling yield and reduced chalky rice percentage but did not significantly affect the large majority of rice nutritional, eating, and cooking quality traits. Zeolite use did not affect rice milling and appearance traits or cooking quality. However, zeolite increased protein concentration and slightly decreased eating score. Growing rice using energy-controlled irrigation integrated with nitrogen and zeolite management system (I_ECN₁₀₅Z₁₀) did not significantly impact any grain traits. The results suggest energy controlled irrigation combined with a reduced rate of nitrogen and an intermediate level of zeolite, benefits farmers through decreasing water and nitrogen fertilizer use, and increasing yield with only minor or no effect upon most grain milling, appearance, nutrition, eating and cooking traits.