Impact of water-nitrogen coupling on grain yield, water and nitrogen usage in zeolite-amended paddy field under alternate wetting and drying irrigation

Abstract: Increasing demand for maintaining yield with reducing environmental and resource costs challenges conventional rice production. Water inputs can be reduced by the use of alternate wetting and drying (AWD) irrigation. And clinoptilolite zeolite (CZ) benefits farmers through decreasing water inputs and N usages in non-irrigated farmland, however, its performance is rarely reported in paddy field, especially under AWD irrigation. In order to clarify the application potential of CZ under AWD irrigation, an experiment was conducted under automatic canopy lysimeters to determine the effects of CZ on rice grain yield and water and nitrogen usage efficiency under different nitrogen application rates and irrigation regimes using the split-split-split plot design. The experimental site was located at the Donggang Experimental Station of New Irrigation Technology, Dandong, China in 2012 and 2013. A japonica rice, Oryza sativa L. cv. Gangyu 6 was cultivated on a silty loam soil. Years after zeolite application were main plots. Two irrigation regimes, continuous flooding and AWD irrigations, were subplots. N application rates (0, 52.5, 105 and 157.5 kg/hm2 N applied as urea) were sub-subplots and CZ application rates (0, 5, 10 and 15 t/hm2 CZ) were sub-sub-sub plots. The experiment was repeated in 2013 but no additional CZ was received, and the plots in 2013 experiment were same as 2012 experiment. Dynamics of soil moisture characteristic curves under different rates of zeolite application were also observed through mixing surface soil samples attained from the experimental site with 0, 5, 10 and 15 t/hm2 in the laboratory. Results indicated that paddy field amended with increasing rates of CZ application significantly increased soil water holding capacity, and improved paddy soil moisture status, when the soil moisture status of paddy surface soil was controlled within the range of -35-0 kPa. At the soil matrix potential of -20 kPa, soil application of 5-15 t/hm2 rates of CZ resulted in 3.0%-6.1% higher volumetric soil water content than zero CZ treatment. The increasing of soil water holding capacity resulted in enhanced water productivity in both continuous flooding and AWD irrigations, while the latter was more obvious. Increasing rate of CZ application significantly improved soil cation exchange capacity and nutrient preserving capability, In particular, the application rate of 105 kg/hm2 nitrogen fertilizer application mixed with 10-15 t/hm2 CZ could significantly improve nitrogen utilization efficiency by 76.8%-87.0% while maintaining normal rice yield. Increasing CZ application also increased grain yield by 4.7%-16.8%, and overcome a slight reduction in grain yield under AWD irrigations at the highest nitrogen rate, as compared to continuous flooding irrigation with the same nitrogen rate. In general, AWD irrigation in combination with 10 t/hm2 CZ and105 kg/hm2 nitrogen fertilizer application was recommended. This rice production system could benefit farmers through reducing 27.8% irrigation water, 33.3% nitrogen application, while increasing 10.6% rice yield, 89.2% nitrogen use efficiency and 52.5% water productivity and these positive effects could last at least 2 years. The proposed production system was also expected to be an available strategy for ecological agriculture for arid and semi-arid area which maintains yield with lower environmental and resource costs by enhancing soil water holding capacity and improving nutrient preserving capability in paddy field due to CZ application.