Mulching Effect On Water Consumption Components And Water Use Efficiency Of Dry Land Maize And Its Simulation

The Loess Plateau in Northwest China accounts for about 55%of the nation's total cultivated land area,which is characterized by a semi-arid climate where water scarcity is the primary limiting factor for agriculture in this region.Adopting alternative field management practices such as mulching practices,subsurface irrigation and crop residue retention to inhibit unproductive water loss for increasing water use efficiency is one of the main objectives for innovating agricultural water management.Evaluating the most reliable mulching type and practice in the Loess Plateau of Northwest China is of great importance for agricultural water management.Therefore,different plastic and straw mulching practices should be tested in dryland maize production.This study compared the effects of different plastic film mulching and straw mulching in dryland maize production.The main objectives of this study were(i)to study the soil moisture status and change in physical and chemical properties,2-dimensional root distribution,yield and economic benefit of maize,(ii)to observe crop growth parameters,the contribution of E/ET,resource capture and resource use efficiency of maize and(iii)to evaluate the performance of AquaCrop model in simulating crop growth,seasonal biomass,grain yield and soil water dynamics under different mulching practices in rainfed conditions.The following results have been achieved:(1)From two annual farmland soil moisture studies of different mulching practices for maize crop,the dynamic characteristics of soil moisture and the law of water balance were basically found out.Based on the in-depth analysis of the data,the law of evaporation and crop transpiration of dryland maize under different mulching conditions was also studied.Moreover,the mechanism,process and approach of regulating the water consumption structure and water consumption components of dryland maize production under different mulching treatments were revealed.Compared to control,non-mulch with conventional flat cultivation(CK),the evaporation rate of plastic film mulching,ridge and non-mulching furrow(RF),full plastic mulching with conventional flat cultivation(FPM),straw mulching with conventional flat cultivation(SM),partial plastic mulching with conventional flat cultivation(PPM)lowered by 33%,57%,13%and 27%,respectively over two growing seasons.By comparing the seasonal soil moisture content(SMC)during two growing seasons,SMC under FPM was 8.4%,0.6%,8.8%and 11.1%more than that of RF,SM,PPM and CK,respectively.The dynamic characteristics of soil water under different mulching conditions and the change of soil evaporation and crop transpiration flow in dryland were also found out.Furthermore,the mechanism of water consumption components and structure of dryland maize production was revealed through two years' observation of farmland water consumption and maize growth under different mulching conditions.It was observed that all the mulching treatments improved root growth in both growing seasons mainly in the top 30 cm soil depth,which led to a distinct effect on grain yield as compared with CK.There was a positive correlation between grain yield and root biomass under sufficient soil moisture,while there was a negative correlation between grain yield and root biomass under deficient soil moisture and at the grain filling stage.The transpiration rate of RF,FPM,SM and PPM was 71%,102%,25%and 44%,respectively higher than that of the CK during the measuring period.(2)The improvement of crop growth development,the increment of grain yield and water use efficiency by saving water under different mulching practices were also validated.It was further confirmed that all mulching treatments could improve stem liquid flow rate and reduce soil evaporation to different degrees,thus reducing E/ET.Consequently,total E/ET of RF,FPM,SM and PPM decreased by 32%,55%,6%and 28%compared with CK over two growing seasons.RF,FPM,SM and PPM were 19.1%,36.6%,15.5%and 8.3%higher in WUEGY,13.0%,20.3%,3.0%and 4.9%higher in RUEGY,18.3%,29.7%,4.1%and 8.4%higher in TUEGY in two growing seasons than that of CK.Among the plastic mulching treatments,FPM could reduce E/ET,improve crop growth,WUE,RUE and TUE than that of RF and PPM.It is noteworthy that full plastic mulching was found as an effective,sustainable system for maize production in the study area.However,it is still needed to consider the environmental problem "white pollution" in the long run,even though the use of the FPM in maize production may serve as a viable tool in reducing production risks in semiarid areas.(3)It was found that AquaCrop could predict canopy coverage,final aboveground biomass and grain yield of spring maize with different mulching and bare fields,and could be used to optimize farmland water management measures.The performance of FAO AquaCrop model version 6.0 was evaluated for predicting maize canopy cover(CC),available soil water,grain yield,crop evapotranspiration(ETc),and water use efficiency(WUE)under different mulching practices for two consecutive seasons in this study.After successful parameterization,simulating canopy cover(CC)was acceptable with R2?0.78,NRMSEs in the range of 12.6 to 24.5%.The model performance relative to the simulation of total SWC was acceptable in the 2018 calibrated year for all treatments.However,the prediction error of the total soil water content of all treatments in 2019 exceeded the recommended threshold of the agricultural model.Therefore,the estimation error of the total SWC in 2019 under all treatments was over the threshold recommended for agricultural models and simulating evapotranspiration in rainfed maize under different mulching practices resulted in high deviations from the 1:1 line.Consequently,the biomass development was simulated slightly well by the model during 2018,but poor accuracy was observed in 2019.However,calibrated and validated final grain yield and biomass yield were observed with acceptable recommended percent deviations(-3.5 and-3.2),and NRMSE(8.8 and 10.1%)over two growing seasons.Considering the robustness of the model,its simplicity and its performances in the current study,AquaCrop could be judged adequate for the prediction of canopy cover,final aboveground biomass and grain yield under different mulch and non-mulch practices in the cultivation of maize in the Loess Plateau of Northwest China.In general,the most important result of this research is to reveal that FPM improved soil moisture,maize root growth and development and sap flow rate,thereby increasing biomass and grain yield in both rainy year(512.3 mm rainfall in 2018)and dry year(203.4 mm rainfall in 2019).