Modeling The Effects Of Plant Density And Straw Mulching On Maize Yield And Field Water

Using the spring maize in Shouyang Dryland Farming Experimental Station in the eastern part of Loess Plateau as the research object,the relationship between precipitation and yield was analyzed with statistical analysis method.The limiting characteristics of precipitation allocation to spring maize yield was determined.Based on the experimental data of Shouyang Station,the Agricultural Production System Simulation Model（APSIM）was calibrated and validated,and then the model was used to analyze the effects of different planting densities and straw mulch rates on maize yield and water balance in past 49 years,and quantify plant density and straw mulch rates to obtain the maximum yield and water use efficiency in different precipitation years.The main results were as follows:（1）The annual precipitation variation of Shouyang Station is very large and the seasonal distribution is extremely uneven.There was significant positive correlation between the maize yield and the precipitation in fallow period.Meanwhile,the yield of maize in Shouyang was related to the distribution of precipitation during the growth period,act as that the maize yield was significantly correlated with the precipitation in June and July,especially in July.（2）Sensitive parameters of that affect the output of the model were confirmed through the sensitivity analysis.Then the sensitive parameters were calibrated according to the field test data and the"trial and error method".The validated results showed that APSIM model could simulate the leaf area index,above ground biomass,accumulated evaporation and yield of maize well at Shouyang Station,but the simulation of soil water content and daily evaporation was poor.Overall,the calibrated APSIM showed good predictability and adaptability in maize production and farmland water simulation in Shouyang Station.（3）Increasing plant density reduced soil evaporation and increased the ratio of transpiration to evaporation.Evapotranspiration increased with increasing of the plant density and showed an asymptotic relation only with the exception of extremely dry years.Planting density had no significant effect on evapotranspiration in extremely dry years.The results of scenario analysis showed that the optimum planting density of maize in Shouyang dryland area increased with the increasing of annual precipitation.The optimum plant density is 32500 plants hm^-2 in extremely dry years,52500 plants hm^-2 in dry years and 67500 plants hm^-2 in normal years,mild wet years and extremely wet years,respectively.（4）Straw mulching significantly reduced soil evaporation,increased yield and water use efficiency,and reduced interannual variability in yield due to seasonal fluctuations of precipitation.The effect of straw mulching on yield and water use efficiency was influenced by the straw mulch rates and precipitation years,which was not obvious at low mulching amount and increased with the increase of straw mulch rates.The maximum yield and water use efficiency were achieved when the straw mulch rates was 100%.The effect of straw mulch on water-saving and yield-increasing decreased with the increasing of annual precipitation,which is the most significant in extremely dry years and the least in extremely wet years.The content of total organic carbon（TOC）decreased with the extension of simulation time and the reduction was the most obvious in 0²0 cm depth.Straw mulching increased soil total organic carbon（SOC）content,and the organic carbon content in 0²00 cm soil layer was balanced when the straw mulching amount was 100%.