| This study in the loess plateau hilly gully region at the same time to mountain apple orchards and conservation agriculture ecological system as the object,the surrounding soil moisture dynamic process and carbon sequestration,water productivity,evapotranspiration,on the basis of field investigation and fixed-point monitoring,with the aid of EPIC?0810?model for the agricultural production system,evaporation,soil moisture,and soil carbon has carried on the quantitative simulation.Based on the meteorological data over the years,the effects of each meteorological factor on evapotranspiration water consumption and carbon storage in farmland orchards were quantitatively analyzed and compared,and the characteristics of evapotranspiration law and dynamic changes of soil organic carbon storage in various systems under different agricultural land use types were analyzed.The main conclusions of this study are as follows;?1?based on field survey and fixed-point monitoring data,we carried out sensitivity analysis and model correction for the EPIC model;For alfalfa,the most sensitive parameters were PHU,DLAI,WA,PARM?42?,PARM?3??0.384,0.294,0.224,0.223,0.210?,and HI?0.634,0.429,and 0.507?.The simulation accuracy of each simulation value of EPIC is from high to low.Yield>Evapotranspiration>Soil moisture>Transpiration.Although the simulation performance of EPIC for the yield and water consumption of four crop systems has been able to meet the requirements of the test,there are still some problems in the simulation of perennial crops.The physiological parameters of perennials were only determined according to the maturity of crops.Therefore,to some extent,the model will overestimate the yield and evapotranspiration consumption in the young and declining stages.Therefore,in the simulation of perennial crops,this paper suggests that the duration should not be too long,and only the physiological period corresponding to parameters should be simulated to ensure the accuracy of simulation values.At the same time,the accuracy of the model for soil water is low,and the reasons need to be further studied and simulated.In order to improve the simulation accuracy,this paper suggests that the unit thickness of soil layer should not be less than 50cm.?2?Based on EPIC,the influence factors of water productivity and soil water dynamics of mature apple forests in different regions of Shaanxi from 1981 to 2016 were compared.The results showed that during the study period,the average annual yield of mature apple forests in the hilly and gully areas of northern Shaanxi?NS?,the Weibei?WB?tableland and the Guanzhong?GZ?plain areas were 16.94,22.62 and 25.70 t·hm-2,the average annual evapotranspiration was 511.2,614.9 and 889.88mm,and the water productivity was 3.81,3.82 and 3.24 kg·m-3,respectively.In NS and WB regions,forest land water stress was the most serious,with the average annual stress days being 54.89 and 28.38 d,respectively.In GZ region,N element stress was more severe,with the average annual stress days being25.87 d.During the simulation,woodland area,area of WB river and the GZ area of Shaanxi apple of total water consumption were 1152.17,1342.95,and 1372.42 mm,2?15m soil reduced rate of the available soil water content were 63.44,57.08,51.41 mm·a-1,deep soil dry layer appear time 8,13 and 17 years respectively,dry layer stability to 11 m deep time of 18,21 and 26 years,respectively.The management focus of different areas should be determined by referring to the leading factor of water productivity.?3?Returning farmland to forest,grassland and conservation agriculture?CA?is an important method to increase vegetation coverage in semi-arid areas of the loess plateau in China to solve desertification and soil erosion.In this study,we simulated the crop water productivity?CWP?,transpiration water consumption ratio?T/ET?and soil water?SWC?of apple forestland,alfalfa,and corn soybean and potato soybean rotation systems by using the comprehensive climate model of environmental policy?EPIC?from the perspectives of productivity stability,water use efficiency and soil desiccation.We conducted parallel experiments from 2013 to 2017,and measured Yield,SWC and ET of each system by neutron tube method,liquid flow method and evapotranspiration apparatus.The results of this study show that;Alfalfa has relatively high WUE,CWP and T/ET up to 4.06kg·m-3 and0.78,respectively,but its productivity stability is poor and stress is serious in the later stage.The biggest advantage of potato soybean rotation system is its relatively low water consumption,which is an important planting method for soil desiccation recovery.It can be seen from the monthly average evapotranspiration change that the overconsumption and water stress of soil water mainly occur in 4-6 month of spring.Uneven distribution of seasonal rainfall is an important reason to limit water use in this area.The historical weather and EPIC weather generator were used to predict the SWC and soil dry layer?DSL?for2018-2030,in which the desiccation of the alfalfa system was the most severe,with permanent dry layer that could not be recovered in a short time.The dry layers of other systems are unstable and will recover in heavy rainfall years.?4?EPIC model was used to evaluate the soil organic carbon?SOC?reserves of two types of protective agriculture?CA?systems and the long-term rain-fed cropping systems of apple woodland and alfalfa in the hilly and gully regions of the loess plateau.Calibrate and verify the average crop yield,biomass and SOC reserves of 4 treatments and 5 major planted crops?corn,potato,soybean,apple and alfalfa?from 2013 to 2017.The results showed that EPIC successfully simulated crop yield,biomass and SOC.However,this model tends to underestimate the SOC of CA and overestimate the SOC of alfalfa and apple.Crop straw has a great effect on soil organic carbon interception.There was an obvious linear regression relationship between soil organic carbon storage,crop residues and reforestation.The historical weather of EPIC automatic production predicted the change trend of soil organic carbon in each system in the next 20 years,among which the soil organic carbon in alfalfa system showed a significant decline trend,and the SOC of CA system and apple woodland system showed an increasing trend,among which the rotation of corn and soybean increased the most.Therefore,CA treatment combined with maize rotation proved to be more effective land management for carbon sequestration and carbon fixation. |
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