Study Of Simulation And Mechanisms For High Use Efficiency Of Water-Nitrogen In A Corn Field Under Biodegradable Film Mulching

Plastic film mulching technology has been widely applied worldwide due to its great advantages,such as saving water,improving the soil temperature,increasing crop yield,and controlling soil salinity,especially in the region with a cold and arid climate.However,the traditional plastic film is mainly made of non-degradable polyethylene or polyvinyl-chloride.Long-term use of plastic film would be leaded to an accumulation of plastic-residues in soil,which caused a series of negative effects on agricultural ecosystem environment and human health.Biodegradable film made of cellulose and starch has been regarded as the important material to overcome"white pollution".Although the effects of biodegradable film mulching on soil water,temperature,nitrogen,salt,corn growth,and water consumption have been fully studied in the previous literature,the research in terms of the mechanism of high use efficiency for water-nitrogen in a corn field under biodegradable film mulching is little.Meanwhile,the impacts of disintegration area on soil water,temperature,nitrogen,and salt have not been considered in the existed models.Therefore,a three-year experiment during 2018-2020 was carried out in the Jiuzhuang comprehensive water-saving experiment site,Hetao irrigation district,Inner Mongolia,to set different strategies of irrigation,N-fertilizer application,and mulching.An expression model considering matter transformation in the soil-plant system under biodegradable film mulching was deduced,and it was used to reveal the dynamics of soil water,heat,nitrogen,salt,enzyme,microbial biomass,water consumption,and corn growth.The optimal strategies of irrigation and nitrogen application were determined,which provided the effective supports of theory and technology for agricultural production under biodegradable film mulching in a cold and arid region.Main contents and conclusions were as follows:1.Spatial-temporal dynamics of soil water,nitrogen,temperature,and salt in a corn field under biodegradable film mulching were quantified.Meanwhile,a multi-factor transport model considering soil water,temperature,nitrogen,and salt under biodegradable film mulching was built based on HYDRUS（2D/3D）model.The responses of soil water,temperature,nitrogen,and salt against to disintegration rate variation were explored.The result showed that the model has the high simulation accuracy with mean relative error of6.5%-14.6%,and the model can precisely capture the dynamics of soil water,heat,nitrogen,and salt under biodegradable film mulching.In the early crop growth stage,the effect of disintegration area of biodegradable film on the transport and transformation of soil solute is little.However,in the middle and late crop growth stages,soil water content and soil temperature decreased by 2.5%and 0.5°C in response to an increasing 20%of disintegration rate of biodegradable film,while soil nitrate and salt increased by 4.0%and11.6%,respectively.2.Differences of soil microbial biomass carbon and nitrogen,and enzymatic activity under biodegradable film mulching with different irrigation and fertilizer application amounts were revealed.The rate of soil microbial death and the turnover time were quantified using the first-order dynamic model.A positive linear correction between soil microbial biomass,soil enzyme activity,and N-fertilizer application amount was found,while soil microbial biomass and soil enzyme activity nonlinearly increased against to an increase of irrigation quota.In general,the highest soil microbial biomass occurred in 22.5mm of irrigation quota and 280 kg ha^-1of N-fertilizer application amount under the irrigation and N-fertilizer coupling application conditions,with soil microbial biomass carbon of 78.5 mg kg^-1,soil microbial biomass nitrogen of 3.2 mg kg^-1,catalase of 2.33glucose g^-1h^-1,sucrase of 0.45 m L 0.1 N KMn O₄g^-1h^-1,urease of 0.026 mg NH+4-N g^-1h^-1,carbon dioxide release rate of 9.7 mg kg^-1d^-1,death rate of 0.12 mg kg^-1d^-1,and the turnover time of 11 d.3.Water consumption characteristics of corn under biodegradable film mulching under different irrigation quotas were investigated.Moreover,an evapotranspiration（ET）model（BSW）under biodegradable film mulching considering the effect of disintegration processes on water consumption was deduced by inducing the disintegration rate.It can be well used to express the ET characteristics under different disintegration rate conditions.The result showed that the accuracy of ET and evaporation（E）estimated by BSW model were great by comparison with measured data from 2018-2019,with the average relative error of 11.4%-15.7%and 6.6%-15.2%for ET and E,respectively.This study further found that the water consumption characteristics of corn was closely related to the variation of leaf area index（LAI）under biodegradable film mulching.When 0<LAI≤2,the ineffective water consumption index（E/ET）decreased in response to an increase of LAI under different irrigation quotas,and the largest E/ET occurred in the 30 mm of irrigation quota.However,there is a parabolic increase trend between E/ET and LAI when 2<LAI≤4.In general,E/ET decreased against in an increase of LAI under different irrigation quotas.The size order of decreasing ratio for E/ET under different irrigation quotas is 30 mm>22.5mm>15 mm.Additionally,E/ET increased by 14.6%in responses to an increase of 20%for the disintegration rate.4.The effects of biodegradable film mulching on the corn growth rate and growth index at daytime and nighttime periods were studied.A growth model for corn under biodegradable film mulching（FCM）was built by inducing the mulching degree,disintegration rate,effectively accumulative surface soil temperature,and the stress coefficient of water,nitrogen,temperature,and salt based on the crop growth model（CM）and the accumulated temperature compensation method.The simulation accuracy of FCM model was apparently higher than that of CM model,in which the normalized root mean square error of LAI,above-ground biomass（AB）,and crop yield（CY）simulated by FCM was 76.9%,1.3%,and 66.6%lower than that of CM,respectively.Meanwhile,the increase ratio of corn growth rate at daytime period was 20.9%higher than that at nighttime period.Additionally,corn yield under biodegradable film mulching decreased by 14.5%and 1.7%in responses to an increase of 25%for disintegration rate and salinity of irrigation water,respectively,while it increased by 41.6%and 36.2%in responses to an increase of 25%for irrigation quota and N-fertilizer application level.However,corn yield decreased by 13.7%against in an increase of N-fertilizer application amount when N-fertilizer application amount exceeds by 280 kg ha^-1.5.The comprehensive benefit evaluation model for corn was provided by combining with different economic and environmental indicators.The optimal strategies of irrigation,N-fertilizer application,and mulching in a cold and arid region were determined through a comprehensive evaluation for agricultural production benefits using the comprehensive evaluation model.Under the same irrigation quota,the comprehensive score increased with an increase of N-fertilizer application amount,while it increased firstly and then decreased in response to an increase of irrigation quota.Under irrigation and N-fertilizer coupling application strategies,the highest comprehensive score occurred in 22.5 mm of irrigation quota and 280 kg ha^-1of N-fertilizer application amount,with comprehensive score of6797.1.Therefore,this study recommends that the most optimal irrigation and N-fertilizer application strategy is 22.5 mm of irrigation quota（the irrigation time is 7-10）and 280 kg ha^-1of N-fertilizer application amount（3-4 application）.