| Xinjiang is short of freshwater and rich in brackish water resources.The combination of brackish water irrigation and drip irrigation under mulch can not only satisfied the water demand of crops,but also alleviate the problem of water resources short.However,long-term brackish water irrigation soil resulted in secondary salinization.In order to explore the characteristics of soil water,fertilizer and salt distribution,nitrogen balance in soil-crop system and suitable irrigation and fertilization system for cotton growth under drip irrigation under mulch,the space-time variability and distribution characteristics of soil bulk density,grain composition,physical parameters,water content,salinity and nutrient content were studied by combining regional investigation with field experiments and geographic information system(GIS)with geostatistics in Baotou Lake area of Kuerle,Xinjiang.Soil nitrogen balance model and cotton growth model were established and validated to determine soil water and nitrogen use efficiency,stress coefficient and irrigation amount.The main conclusions were as follows:(1)In the study area of 0-60 cm soil layer was showed that the soil particle composition was moderately variable,soil bulk density and other physical property parameters were moderately weak variability.The fractal dimension of soil volume was logarithmically related to clay,positively related to silt and negatively related to sand.(2)The water,fertilizer and salt submitted to normal distribution,showed moderate variability and could be fitted by Gaussian model(0?20 cm and 60?80 cm ammonium nitrogen could be fitted by Exponential model)in root zone.These have strong and medium spatial correlation and the range is between 1 and 1.5km,while ammonium nitrogen range is much larger than 1.5 km.The soil water content and nutrient content increased first and then decreased with the growth period.while salt content increased gradually,which showed moderate variability.The semi-variogram of water content,nutrient content and salt content expressed Gaussian model(ammonium nitrogen content expressed Index model),which have strong spatial correlation.The water consumption of cotton in root zone increased first and then decreased,the maximum was reached at boll stage.The soil content of water,fertilizer and salt were affected by structural factors in depth,climate and human activities in time,and their spatial distribution was mostly massive.(3)A combined soil water-nitrogen transport and crop growth model was established and validated based on the field date.The results showed that the simulated values of soil-crop nitrogen balance model was well fit with the observed values,but the model slightly underestimated soil nitrogen content.The determination coeff-icient R2 was 0.565,root-mean-square erro RMSE was 9.67,coincidence D was 0.82,residual aggregation coefficient CRM was 0.17 and the average relative error Re was-14.3%.Water and nitrogen use efficiency were 1.579 kg/m3 and 44.898 kg/kg,respectively,and the growth of cotton was not affected by water and nitrogen stress.(4)The change of cotton plant height,leaf area index and aboveground biomass can be better described by Logsitic model and modified Logistic model over effective accumulated temperature(time).The cotton growth model with drip irrigation under brackish water film was established based on AquaCrop model,which can better simulate the change of canopy coverage,biomass and yield(R2>0.546,RMSE<6.209,D<0.832,CRM<0.166).But the simulated yield and biomass were lower than observed.The appropriate brackish water irrigation amounts for cotton growth was determined in silty loam and sandy loam which was 300-400 m3/mu,according to different scenario simulations. |
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