Modelling Spatiotemporal Variation Of Spring Maize Water Productivity In Northern Rain-fed Cropland

The shortage of water resources is an important factor restricting the sustainable development of agriculture in China.As a large agricultural country,irrigated agriculture accounts for 62.3%of the consumption of freshwater resources in China.With the continuous growth of China’s population,the continuous development of industry,and the emergence of various environmental problems,the water resources available for irrigated agriculture are gradually decreasing,and the continuous expansion of irrigated area is approaching its limit.However,dryland farming in the rain-fed areas of northern China,has great potential to increase production.At present,the negative effects of climate change on agricultural production have brought great challenges to China’s food security and stability.As an important grain production base in China,the sustainable development of local agricultural production has been seriously affected by the uneven distribution of rainfall and frequent droughts in the northern arid area.Therefore,it is of strategic significance to accurately assess the temporal and spatial variation characteristics of farmland water productivity and its influencing factors in the arid region of northern China under the conditions of climate change,and to improve the farmland water productivity in the arid region of northern China for ensuring national food security and alleviating water shortage.Based on the ecosystem process model--CEVSA2 model,this paper increased the quantitative description of crop yield formation process,developed its agricultural version--Agro-CEVSA model,and used field observation and survey data to calibrate and verify the improved Agro-CEVSA model.The model was applied to simulate the crop yield,evapotranspiration and water productivity of spring maize in the northern dryland region from 1985 to 2017,providing a theoretical basis for formulating the suitable agricultural production model and taking reasonable farmland management measures in the future.The main results are as follows:（1）The improved Agro-CEVSA model was verified by using the flux observation data of two spring maize farmland ecosystems in Shouyang,Shanxi Province and Jinzhou,Liaoning Province.The results showed that the Agro-CEVSA model of spring corn farmland gross primary productivity（GPP）,ecosystem（Re）and breathing net ecosystem productivity（NEP）of simulated values and observed values has good consistency,the model can well simulate photosynthesis,respiration and spring corn farmland ecosystem net carbon exchange of seasonal and interannual dynamic.By collecting the spring maize yield of each county and the simulation results of other models and comparing with the Agro-CEVSA model,the results show that the model has a high accuracy in simulating the spring maize yield in farmland.（2）From 1985 to 2017,the spatial distribution characteristics of spring maize farmland in the northern dryland region were higher in the southeast and lower in the northwest.The average annual yield was 8439.76kg·hm^-2,and the trend rate was 165.59kg·hm^-2·10a^-1.The annual yield changed greatly in the early period of the study period,and was relatively stable after 2004.（3）The spatial distribution of spring maize evapotranspiration decreased from southeast to northwest in the rain-fed area of northern China.From 1985 to 2017,the interannual variation of spring maize evapotranspiration in northern arid areas ranged from 378.60 to 532.51kg·hm^-2,with a trend rate of 4.08mm·10a^-1.The evapotranspiration of different types of rain-fed areas showed the Semi-humid region>Subhumid and arid region>Half arid area>Semi-arid and Arid area>Arid area.（4）The spatial distribution of spring maize water productivity in the northern arid area was higher in the north and lower in the south,with a range of 1.27～3.92kg·m^-3.From 1985 to 2017,the average water productivity of spring maize was 1.84 kg·m^-3in the northern arid area,and the trend rate was 0.03kg·m^-3·10a^-1.Except for the arid area,there was little difference in the water productivity of spring maize fields in other types of arid areas.（5）The spatial distribution of spring maize water productivity was positively correlated with temperature and rainfall in the northern rain-fed area.Water productivity is more determined by crop yield than by crop water consumption in the northern dryland.With improved farmland management,the fluctuations in yields caused by climate change are gradually diminishing.Due to the continuous increase of spring maize yield,but the increase of water consumption is less than the increase of crop yield,so the water productivity of farmland can be continuously improved.Due to climate change,crop varieties and human management and other factors will affect the formation of crop yield and water dissipation in farmland.Therefore,it is the future direction of Agro-CEVSA model to further improve the model and improve the influencing mechanism of crop yield formation process and water productivity,so as to simulate future crop water productivity dynamics.