Dynamic Response Of Root-shoot Growth Of Summer Maize To Soil Moisture Under Deficit Irrigation

Deficit irrigation is a method of reasonable adjustment of irrigation system,allowing yield to be reduced,and maximizing water use efficiency.Three irrigation levels（full irrigation:100%ET_a;Moderate water deficit:80%ET_a;Severe water deficit:60%ET_a,where ET_a is the evapotranspiration measured by the lysimeter under sufficient irrigation conditions）were set at three growth stages of summer maize（emergence to jointing stage,jointing to tasseling stage,tasseling to filling stage）.Nine deficit irrigation treatments were designed with different degrees.By analyzing the temporal and spatial variation of root characteristic parameters（root length density,root surface area and root weight）,aboveground growth index（plant height and leaf area index）,soil water consumption and evapotranspiration under different water supply conditions,the dynamic response of summer maize root and crown growth to soil moisture were explored.The main results are as follows:（1）The response of root distribution to water stress in summer maize was revealed.The correlation between yield and root characteristic parameters at each growth stage was clarified.The response of root growth to soil moisture was determined.The root length density,root surface area and root weight gradually decreased with soil depth.Moderate water deficit during emergence to jointing stage and full irrigation during jointing to tasseling stage significantly increased the root growth rate of deep soil,and the average root length density（0-60 cm）was 10.39%higher than that of full irrigation.The increase of root length after full irrigation was higher than that of root surface and root weight.Water deficit at jointing to tasseling stage,root indexes could not recover to normal level after full irrigation at tasseling to filling stage,but full irrigation at different growth stages delayed root senescence.The root growth was mainly affected by soil moisture.The soil moisture at jointing to tasseling stage not only had an extremely significant impact on the current root surface and root weight（P<0.01）,but also significantly affected the root development at tasseling to filling stage.The effect of water stress on root growth had a lag effect.（2）The influence of water regulation on soil water consumption and evapotranspiration of summer maize was explored,and the correlation between evapotranspiration and soil moisture content was clarified.The main water consumption layers of emergence to jointing stage,jointing to tasseling stage,tasseling to filling stage and filling to maturity stage were 0-40,0-40,0-60 and 20-60 cm,respectively.Moderate water deficit during emergence to jointing stage and sufficient irrigation during jointing to tasseling stage increased soil water consumption in 40-60 cm soil layer,and improved the drought resistance of re-water deficit during tasseling to filling stage,which was mainly related to the increase of root length density in 40-60 cm.Variation of soil water storage reached the maximum after each irrigation,and then decreased with fluctuation.The fluctuation peak was mainly affected by temperature,irrigation amount and time.The hourly evapotranspiration ET_r peaked at 12:00-16:00.The ET_rpeaked were affected by deficit and growth stages.The maximum daily evapotranspiration ET_c occurred at jointing to tasseling stage or tasseling to filling stage,reaching 5.19-7.93 mm d^-1.Moderate water deficit during emergence to jointing stage,ET_c returned to normal level after full irrigation during jointing to tasseling stage.In jointing to tasseling stage,ET_c recovery ability decreased.The relationship between evapotranspiration and soil moisture content was constructed.In tasseling to filling stage,when soil moisture content was less than 75%of field capacity,the relationship between evapotranspiration and soil moisture content was positively correlated.When the soil moisture content was greater than 75%of field capacity,the evapotranspiration of summer maize remained basically unchanged.When the soil moisture content is reduced to 50%field capacity,the crop basically stopped growing.（3）The changes of aboveground growth,yield and water use efficiency of summer maize under different water conditions were analyzed,and relationship between yield and root characteristic parameters was determined.Moderate water deficit during emergence to jointing stage and full irrigation during jointing to tasseling stage had a compensatory effect on the growth of plant height and leaf area of summer maize and returned to normal level during tasseling to filling early stage（August 20）.Moderate water deficit during jointing to tasseling stage and full irrigation during tasseling to filling stage were beneficial to the transfer of assimilates to maize reproductive organs.Deficit irrigation can improve the root-shoot ratio of summer maize,priority to ensure root growth and development.Severe water deficit in the early stage,the root-shoot ratio was reduced after full irrigation during tasseling to filling stage,and promote the priority of photosynthate distribution to maize spike,which slowed down the impact of water deficit on yield.Compared with full irrigation,the yield of moderate water deficit during emergence to jointing stage,full irrigation during jointing to tasseling stage,and moderate water deficit during tasseling to filling stage decreased by 5.85%,and the water use efficiency increased by 4.07%.At tasseling to filling stage,the yield of summer maize was significantly positively correlated with the root characteristic parameters（P<0.01）,followed by filling to maturity stage and jointing to tasseling stage.This paper only analyzed the test data of one year,and it was carried out under the canopy.Its universality needs to be further studied.