Effect Of Clinoptilolite Zeolite On Ammonia Volatilization And N Leaching Loss Under AWD In Paddy Rice

The shortage of water resources and agricultural non-point source pollution by N loss have become an important limitation to the sustainable development of rice production systems.Therefore,it is important to study how to reduce resource and environmental costs,while ensuring the safety of rice production.As an effective water-saving irrigation method,alternate wetting and drying irrigation（AWD）has been widely adopted,however,the alternate aerobic and anaerobic condition under AWD may change the pattern of N loss in paddy fields.Clinoptilolite zeolite（Z）characterized by water holding and preserving N capacity in soil,can reduce nitrogen loss by ammonia（NH3）volatilization,N leaching,N runoff and other pathways,improve plant N accumulation and crop yield.Significant effects have been achieved in many incubation experiments and studies of upland crops.To date,no work has been done to evaluate the effects of Z amendment on N loss in paddy fields,especially under AWD.Therefore,Z was applied to AWD rice production system,with the AWD saving water consumption,and Z reducing N loss and improving grain yield,which will further achieve high production,efficiency and eco-friendly cultivation of rice.A field experiment with lysimeter was carried out in a split plot design with two irrigation regimes（CF and AWD）and three Z amendment rates（0 t·ha-1,5 t·ha-1 and 10 t·ha-1）in Donggang,Liaoning Province in 2016 and 2017.The change characteristics of N concentration in floodwater,NH3 volatilization,N leaching,plant N accumulation,distribution and translocation,inorganic N content in soil,morphophysiological characteristics,rice grain yield,water usage and grain quality characteristics were studied.The following were the main results:（1）The peak value of NH₄⁺-N concentration appeared within 3 days after each fertilization.During the basal fertilization and the first topdressing stages,the NH₄⁺-N concentration in AWD was higher than that in CF;During the second topdressing stage,the NH₄⁺-N concentration in AWD was significantly lower than that in CF.Under the two irrigation regimes,NH₄⁺-N concentration in floodwater decreased significantly with increasing rates of Z addition.NH3 volatilization fluxes generally peaked 3⁵ days after each split N fertilization,and most of the NH3 volatilization occurred within 7¹0 days after fertilization.AWD significantly increased NH3 volatilization during the basal fertilization stage,reduced it during the second topdressing stage,and finally reduced total NH3 volatilization loss,but the reduction was small（<2 kg ha-1）.The NH₄⁺-N concentration in the floodwater for each fertilization period was significantly positively correlated with the NH3 volatilization.Z addition significantly reduced the NH3 volatilization during each fertilization stage by reducing the NH₄⁺-N concentration in floodwater.Total NH3 volatilization of ICFZ10 and IAWDZ10 treatments were lowest,about 35.1%³6.5% and 38.5%⁴0.6% less than ICFZ0 treatment,respectively for the 2 years.（2）During most of the rice-growing period,NH₄⁺-N and NO3--N concentrations in leachate in AWD were greater than those in CF.However,NH₄⁺-N and NO3--N concentrations decreased significantly with the increasing rates of Z addition under the two irrigation regimes,and finally,the total NH₄⁺-N and NO3--N leaching were reduced.Total NO3--N leaching were higher than NH₄⁺-N.In all treatments,the statistically highest value of N leaching was noticed in IAWDZ0 treatment;however,the difference between IAWDZ10 and ICFZ0 treatments was not significant,even IAWDZ10 was significantly lower than ICFZ0 treatment for NH₄⁺-N leaching in 2017.These suggest that the increased N leaching caused by AWD is well counteracted by Z amendment,especially at the higher rate.（3）Compared with CF,AWD reduced the aboveground N accumulation except for tillering stage.At maturity stage,compared with CF,AWD increased the root N accumulation and distribution,didn’t have significant effect on plant total N accumulation,and reduced N translocation in 2017.Z application increased N accumulation in each tissue after panicleinitiation stage.The application of 5 t Z ha-1 and 10 t Z ha-1 improved plant total N accumulation by 12.2% and 16.7%¹8.0% in two years,and also N translocation.（4）During most of the rice-growing period,the NH₄⁺-N and NO3--N content in 0-30 cm soil depth for AWD was higher than in CF.The inorganic N content in 0-30 cm soil depth was also increased by Z amendment,the application of 5 t Z ha-1 and 10 t Z ha-1 increased the mean value of NH₄⁺-N content by 27.4% and 41.5%,and the mean value of NO3--N by 15.1% and 24.7%,respectively.At maturity stage,AWD significantly increased the inorganic N content in soil at the depths of 0-30 cm and 30-60 cm.Compared with the control（no zeolite addition）,the application of 5 t Z ha-1 and 10 t Z ha-1 increased the inorganic N content in 0-30 cm soil depth by 12.1%¹2.5% and 18.7%²0.9%;reduced it in 30-60 cm soil depth by 17.6%²0.2% and 29.3%³1.5% in two years.（5）Compared with CF,AWD reduced the plant height,tiller number,LAI,root bleeding intensity and leaf SPAD value,aboveground dry matter accumulation（DMA）after panicleinitiation stage,and improved dry matter translocation（DMT）in 2016,but not in 2017.The addition of Z increased the plant height,tiller number,LAI,root bleeding intensity and leaf SPAD value,DMA after panicle-initiation stage,also increased DMT.（6）Compared with CF,AWD significantly reduced water usage and increased water productivity;but did not affect rice grain yield in 2016 and reduced it in 2017 without Z amendment.Z application significantly increased panicles per m2,and then grain yield,which in turn improved water productivity（WP）.Rice grain yield and WP for AWD was lower than CF at an application rate of 5 t Z ha-1,but the difference between them was not significant when10 t Z ha-1 was applied.These suggest that higher rate of Z should be applied to increase grain yield and WP under AWD.Compared with CF,AWD significantly reduced head rice rate,but also reduced chalky rice rate and chalkiness;and increased the breakdown and reducing the setback,and then improved the taste value.Z application significantly improved protein content,reduced breakdown and setback,but increased chalky rice rate and chalkiness.（7）Integration of AWD with 10 t Z ha-1 significantly improved available N in shallow soil,which reduced the NH3 volatilization loss（38.5%⁴0.6%）without increasing the N leaching,promoted the N accumulation and plant growth,and then increased the rice grain yield（6.2%⁸.3%）and WP（19.4%²1.3%）,as compared to conventional management（CF without Z application）.The research results provide a new way to reduce rice production water consumption,N resource consumption and environmental costs while achieving higher or similar rice grain yield.