Effect Of Clinoptilolite Application On Rice Growth,Nitrogen And Phosphorus Utilization In Paddy Field Under Energy-controlled Irrigation

With the increasing severity of water shortage and environmental risk induced by overfertilization,studying the efficient paddy field management strategy to reduce water and fertilizer resources consumption and environment cost under the premise of achieving high rice yield is of great importance to ensure food security and agricultural sustainable development.The energy-controlled irrigation（EC）which developed based on alternate wetting and drying irrigation（AWD）could achieve the dual goal of saving irrigation water and maintaining or even increasing rice grain yield.However,it may result in large amounts of nitrogen losses,reduce nitrogen and phosphorus use efficiency,and cause serious environmental pollution.Therefore,clinoptilolite—a naturally occurred inorganic material which characterized by preserving nitrogen,increasing phosphorus availability and water holding capacity in soil—was applied to water-saving paddy field,with the EC regime saving irrigation water and maintaining rice grain yield and clinoptilolite improving phosphorus and nitrogen utilization through its intensive affinity for NH₄⁺,which will decrease nitrogen leaching and alleviate groundwater nitrate contamination,and further improve rice grain yield.In present study,a split plot experimental design was conducted with lysimeters to investigate the effects of different irrigation regimes and zeolite applications on morpho-physiological characteristics,grain yield,and grain quality of rice,inorganic nitrogen content in leachate and soil,and water use,and elucidate the nitrogen-preserving and yield-increasing mechanisms by zeolite.The laboratory experiment was carried out to investigate the effect of different zeolite rates on soil water holding capacity,so as to clarify the water-saving mechanism by zeolite.Furthermore,a split-split plot experimental design was conducted to investigate the effect of clinoptilolite on soil available phosphorus,aboveground phosphorus uptake,shoot biomass,grain yield,and water use in rice under different irrigation and phosphorus managements,and clarify the yield-increasing by zeolite through improving phosphorus utilization.The main results are as follows:（1）Zeolite applied to paddy field with rate of 15 t·ha^–1 significantly increased tiller number,leaf area index,leaf SPAD value,and photosynthetic rate of rice.Also,aboveground dry weight,harvest index,grain yield,effective panicles,and spikelets per panicle of rice were remarkably increased with zeolite application.Zeolite treatment increased rice grain yield by 7.5%,relative to the unamended control.In terms of yield components,the increased yield induced by zeolite could be attributed to the increase of effective panicles and spikelets per panicle.Regression analysis showed that grain yield was positively correlated with leaf photosynthetic rate,and leaf photosynthetic rate was positively correlated with leaf SPAD value,which indicated that zeolite could increase grain yield through improving these morpho-physiological traits.Compared with conventional flooding irrigation（CF）,AWD significantly decreased tiller number,leaf area index,leaf SPAD value,and photosynthetic rate,while EC maintained these traits.Compared with CF,AWD decreased grain yield by 15.3%.However,EC obtained similar grain yield with CF,suggesting that EC could not only save irrigation water use,but also sustain high rice yield.（2）Compared with the CF regime,EC and AWD regimes improved milling quality by increasing milled rice rate and head rice rate,improved appearance quality through reducing chalkiness and chalky rice rate,and improved part of the starch viscosity properties,suggesting that suitable AWD regime could improve rice grain quality.Moreover,zeolite increased head rice rate and improved appearance quality,but had no significant effect on starch viscosity properties.（3）During the rice growing season,the EC and AWD regimes both decreased NH₄⁺-N concentration and increased NO₃^–-N concentration in the leaching,relative to the CF regime,which suggests that water-saving irrigation strengthened nitrate leaching in the paddy field.Zeolite significantly increased soil cation exchange capacity and aboveground N uptake in rice.Zeolite reduced NH₄⁺-N and NO₃^–-N concentration of the leaching averagely by 6.5%and14.7%,respectively.At harvest,zeolite increased NH₄⁺-N content of both surface（0³0 cm）and deep（30⁶0 cm）soil layer,and the increase was more evident in surface soil layer.Zeolite increased NH₄⁺-N content in surface layer and decreased NO₃^–-N content in deep layer,suggesting that zeolite retained more NO₃^–-N in surface layer and prevented it from migrating into deeper layer.All of these indicated that zeolite applied into paddy field could improve inorganic nitrogen retention in soil and N uptake and utilization by rice plant,reduce nitrogen losses in paddy field,and alleviate groundwater nitrate pollution.（4）Water holding capacity of soil increased with zeolite rates.And the water retention effect by zeolite enhanced with water stress intensity,indicating that zeolite could effectively alleviate the adverse impact of water stress on rice plant.Within the soil water potential（SWP）threshold of EC and AWD regimes,i.e.,when SWP was–5,–10,–15,–20,–25,and–35 kPa,soil water content with zeolite application(15 t·ha^–1)was increased by 2.9%,5.4%,7.8%,10.1%,12.1%,and 15.5%,respectively,relative to the unamended control.Zeolite slightly decreased total water use and increased water use efficiency by 9.2%.Compared with the CF treatment,EC and AWD treatments reduced total water use by 14.8%and 25.4%,respectively,and increased water use efficiency by 15.5%and 13.3%,respectively.The EC regime in combination with zeolite rate of 15 t·ha^–1(I_ECZ₁₅ treatment)obtained the highest water use efficiency.（5）Zeolite significantly increased soil available P and aboveground P uptake in rice.Rice grain yield showed a quadratic relationship with aboveground P uptake,and increased with aboveground P uptake,suggesting that zeolite increased rice grain yield through improving aboveground P uptake.Furthermore,the increase of soil available P by zeolite was more evident under EC than under CF,indicating that zeolite could effectively relieve the limitation of water stress on availability of soil P.In conclusion,conventional phosphorus application rate(60 kg·ha^–1)in combination with zeolite rate of 15 t·ha^–1 under energy-controlled irrigation(I_ECP₆₀Z₁₅ treatment)could not only save irrigation water use,increase rice grain yield,and improve rice grain quality,but also alleviate groundwater contamination caused by NO₃^–-N leaching in water-saving paddy field.Therefore,it could provide theoretical foundation for the realization of comprehensive paddy field management which aims to save irrigation water,produce high rice yield,have good rice quality,and protect environment.