Effect Of Irrigation Volume And Its Uniformity On The Spatial Distribution Of Water Below The Canopy For Winter Wheat And On That Of Soil Moisture

Sprinkler uniformity is an important parameter to evaluate the quality of sprinkler irrigation and the design of sprinkler irrigation system,however,when the crop canopy develops,the canopy will redistribute the sprinkler irrigation water,which will influence the redistribution of sprinkler irrigation water in the soil and finally the growth of the crop.In order to establish the design and evaluation standard of sprinkler uniformity,it is significant to study the law of redistribution of sprinkler water by crop canopy and explore the influence of sprinkler water and its uniformity on spatial distribution of soil water,growth condition and yield of crop.This study used winter wheat as the experiment crop,a field sprinkler irrigation experiment was conducted in Jintan District,Changzhou City,from 2020 to 2021.The experiment was based on the crop water requirements with three sprinkler water（W1:full irrigation,W2:2/3 water requirement,W3:1/3 water requirement）treatments and two sprinkler uniformity（J1:75%,J2:55%）treatments.The spatial distribution of sprinkler water above and below the canopy was measured by rain gauges above and below canopy and a homemade stem flow collector,and the spatial distribution of soil water,growth condition and yield of winter wheat after sprinkler irrigation were observed to construct a predictive model for the distribution of water below the canopy of winter wheat under sprinkler irrigation conditions,and to investigate the relationship between soil moisture indicators and winter wheat yield and yield coefficient of variation.In addition,a sprinkler water infiltration model was developed and validated based on COMSOL software,which was used to predict the spatial distribution of soil moisture after sprinkler irrigation with infiltration time and to study the effects of rainfall on the spatial distribution of soil moisture after sprinkler irrigation.The main research results are as follows:（1）Redistribution of sprinkler irrigation water by the winter wheat canopy.During the plucking-maturity period of winter wheat,the spatial distribution of water above and below the canopy was highly significantly correlated（P<0.01）during the plucking-maturity period of winter wheat,and the uniformity of sprinkler irrigation above the canopy was about 1.5%higher than that below the canopy.The throughfall,stemflow,and below-canopy sprinkler losses（Wind Drift and Evaporation Losses,WDEL）created by sprinkler water redistribution through the canopy ranged from 56.0%to 73.9%,25.0%to 37.0%,and 2.5%to 12.7%of the water above the canopy,respectively.While the canopy storage capacity of winter wheat is relatively stable from late nodulation to the filling stage,about 1.3 mm,WDEL cannot be approximated as the canopy interception（WDEL of W1J1 treatment reaches about 3 times the canopy storage capacity of winter wheat）Below-canopy throughfall rate and stemflow rate were negatively（P<0.01）and positively（P<0.01）correlated with LAI,and positively（P<0.01）and negatively（P<0.01）correlated with plant height,respectively,while they were less affected by sprinkler uniformity and irrigation volume.The coefficient of variation of stemflow rate was higher than the coefficient of variation of throughfall rate.（2）Effect of sprinkler irrigation volume and its uniformity on the spatial distribution of soil moisture.The effects of irrigation volume,sprinkler uniformity and the interaction of the two on the uniformity of soil water content from 0 to 30 cm depth were not significant（P>0.05）.Low sprinkler uniformity（J2）and deficit irrigation（W2,W3）lead to an increase in the coefficient of variation(CV_SFC)of soil water(SWC_FC)that can be fully absorbed and used by winter wheat roots(SWC_FC is the difference between soil water content and 65%field water holding capacity,CV_SFCis the coefficient of variation of SWC_FC).（3）Based on the simulation of soil water infiltration by sprinkler irrigation with COMSOL software,we found that:after two days of sprinkler irrigation,the soil water distribution tends to be stable,the soil water distribution will be improved to a certain extent under the water transport caused by the soil water potential difference,but there is still a large gap between the water concentration area and the water deficit area.The CV_SFC at 0-10 cm depth will decrease rapidly under the effect of rainfall infiltration,and the sensitivity of CV_SFC at>10-30 cm depth to rainfall is lower than that at 0-10 cm depth,and there exists a hysteresis;during the period of no rainfall and sprinkler irrigation,the CV_SFC gradually increased from 0 to 30 cm depth under the effect of evaporation,which was especially evident in the soil from 0 to 10 cm depth.（4）Response of winter wheat growth characteristics and yield to sprinkler irrigation water and its uniformity.Under full irrigation（W1）,J2 treatment had no significant effect（P>0.05）on plant height and Leaf Area Index（LAI）of winter wheat.Under deficit irrigation conditions（W2,W3）,the J2 treatment resulted in a slightly increased coefficient of variation in LAI and plant height of winter wheat.Low sprinkler uniformity（J2）led to regional water deficit in the soil,resulting in a slight reduction in crop yield in the region under water stress and an increase in yield CV,which was exacerbated by deficit irrigation（soil water content below 65%field holding capacity in about 1/3 of the area in the W3J2 treatment）and a significant reduction in crop yield（9%reduction in yield in the W3J2 treatment and an increase in CV to 0.17）,and spike number and thousand grain quality were the main factors contributing to yield.The combination of irrigation and sprinkler uniformity played a dominant role in the effect of irrigation water on yield.Winter wheat yield and yield coefficient of variation were significantly correlated（P<0.05）with CV_SFCin soil>0-20 cm depth 24 h after sprinkler irrigation.（5）The water balance of the farmland analysis.In the early stage of growth,the precipitation at the experiment site can meet the crop evapotranspiration water consumption,and will produce69.61-74.28 mm surface runoff;in the plucking to filling period of winter wheat,the crop needs more water and the precipitation cannot meet its water consumption,so it is recommended to irrigate;in the late filling period,the precipitation is concentrated and can meet the crop water consumption,so it is recommended to irrigate a lesser volume or no irrigation according to the actual weather condition of the year.Considering the preliminary input of sprinkler system,operation cost and local water quantity,it is recommended to fully irrigate（W1）at low sprinkler uniformity（J2=55%）.