| The uniformity of sprinkler water distribution and the state of existence of droplet motion properties(strike kinetic energy,droplet diameter,velocity and landing angle)directly affect surface runoff,soil erosion,the efficiency of water and fertiliser use and crop yield in agricultural ecosystems,and are important indicators of the hydraulic performance of sprinkler irrigation technology and equipment and the prospects for their application.The interaction between sprinkler water droplets and the crop canopy covering the ground will significantly affect and change the water uniformity and droplet motion properties of the original sprinkler irrigation.However,the interaction mechanism between sprinkler water droplets and the crop canopy is still unclear,and the distributional characteristics of sprinkler water and the existing state of droplet movement characteristics under the crop canopy have not been clarified,and it is not known whether the presence of the crop canopy affects the effectiveness of sprinkler water and has a guiding value in the rational evaluation and assessment of the prospects for the application of sprinkler irrigation technology and equipment.Based on theoretical analysis,model development and multi-objective evaluation,maize canopy,sprinkler intensity and droplet size have been studied in terms of their influence on the repartition and redistribution of sprinkler water and the variability of spatial and temporal distribution of droplet motion properties,as well as the influence of maize canopy on the flight path of sprinkler droplets at different landing angles,and the following conclusions have been drawn.(1)The different maize growth stages corresponding to interception rate,stem flow rate and through rain rate were 6.20%,12.22%,81.58%(the jointing);12.53%,22.25%,65.22%(the flare opening stage);17.28%,35.19%,47.53%(the tasseling stage);17.88%,36.30% and 45.82%(the filling stage).The higher the sprinkler intensity,the more drastic the repartition of sprinkler water by the maize canopy.The mechanisms by which droplet diameter affected canopy interception,stem flow and through-rain generation processes were not consistent.Maize canopy had a negative effect on the uniform distribution of sprinkler water,while sprinkler intensity and droplet diameter improved the heterogeneity of the spatial distribution of sprinkler water under the canopy.The spatial distribution of throughfall rain during the maize pulling and trumpeting stages was characterised by a greater amount of water at greater distances from the stem.At later growth stages,there was a tendency for the larger throughfall rainfall to shift in the direction of the maize row.Sprinkler water under the canopy was mainly distributed over the maize plant rows rather than in other locations between the rows.(2)There was a negative power function correlation between interception rate and stem flow rate and the percentage of throughfall kinetic energy,while the throughfall rate was linearly positive.The higher the sprinkler intensity and droplet diameter,the higher the kinetic energy of the sprinkler droplets under the canopy.Maize canopy had a significant dissipative effect on the kinetic energy of sprinkler drops,which became more pronounced as the maize plant grew.The reduction levels of kinetic energy per unit volume of water droplets for the different growth stages of sprinkler irrigation were 23.15%(the jointing stage),39.06%(the flare opening stage),68.15%(the tasseling stage)and 70.00%(the filling stage).Significant energy aggregation occurred at some of the measured points under the maize canopy when the spray irrigation droplets were small,and the higher the spray irrigation intensity,the more pronounced the energy aggregation.The spatial coefficient of variation of the kinetic energy of sprinkler water droplet under the maize canopy was large,and sprinkler intensity and droplet diameter had an effect on the spatial coefficient of variation of the kinetic energy of the throughfall water droplets.In the early stage of maize growth,the spatial and temporal distribution of droplet kinetic energy under the canopy was very similar to that of throughfall.In the later stages of growth,the spatial and temporal distribution of the kinetic energy of throughfall rainfall was the result of the combined effect of sprinkler intensity,droplet size and maize canopy.(3)Only when the water droplet size was 1.48 mm or less did the size of the throughfall water droplets tended to increase.The size of the throughfall water droplets gradually increased from 1.48 mm to 1.72 mm(the jointing stage),1.95 mm(the flare opening stage),2.17 mm(the tasseling stage),and 2.31 mm(the filling stage)for the different growth stages of maize.The higher the sprinkler intensity,the larger the throughfall water droplet size.The higher the sprinkler intensity,the lower the spatial coefficient of variation of the throughfall droplet size.Maize canopy had a negative effect on the spatial coefficient of variation of throughfall droplet size.In the early stage of maize growth,the spatial distribution of throughfall droplet size was characterised by a greater value the further away from the stem it was.During the tasseling and filling stage,the maize canopy and sprinkler droplet size were the main factors influencing the spatial distribution of the throughfall droplet size.Based on the drop size distribution of the droplet population,differences in the volume of dripping and broken inadequate droplets at different measurement points were responsible for the spatial distribution characteristics of throughfall droplet diameter during the late maize growth stage.The higher the sprinkler intensity and droplet size,the larger the throughfall water droplet velocity.Maize canopy had a reducing effect on sprinkler droplet velocity.The reduction levels for different growth stages corresponded to20.86%(the jointing stage),39.75%(the flare opening stage),73.47%(the tasseling stage),and 73.81%(the filling stage).Maize canopy,sprinkler intensity,and droplet size had a positive effect on the coefficient of spatial variation of throughfall droplet velocity.In the early stages of maize growth,the spatial distribution of throughfall droplet velocity was characterised by greater values at further distances from the maize stem.However,in the later stages of maize growth,the spatial distribution of throughfall droplet velocity was determined by the structure of the maize canopy and the sprinkler droplet diameter.Based on the drop velocity distribution of the droplet population,the differences in droplet velocity at different measurement points were mainly reflected in the equivalent velocity of the larger droplet size in the droplet population.(4)With decreasing sprinkler droplet landing angle,the diameter and velocity of the sprinkler droplets under the maize canopy also tended to decrease,without significant changes in the landing angle or flight path of the throughfall droplets.When the sprinkler droplet landing angle was greater than 45°,the spatial distribution of the sprinkler droplets diameter and velocity under the maize canopy was basically consistent with the maize canopy structure and the leaf projection area.However,when the sprinkler droplet landing angle was less than 45°,the spatial distribution pattern of the sprinkler droplet diameter and velocity under the maize canopy changed considerably,with the larger values of the throughfsll droplet diameter and velocity mainly distributed in the upper part of the maize canopy void.The influence of maize canopy and sprinkler droplet landing angle on the spatial distribution of throughfall droplet landing angle was not significant.The spatial distribution of the throughfall droplet landing angles at the micro-scale spatial scope mainly showed a spatial distribution pattern of large on both sides and small in the middle.Although the maize canopy had a certain degree of disturbance on the velocity and kinetic energy of the drops with larger kinetic energy,it did not significantly change the flight path of these drops.With decreasing sprinkler droplet landing angles,there was a gradual shift towards zero in the trend line of the drop size distribution of the sprinkler droplet population under the maize canopy.(5)In the early stages of maize growth,it was recommended to use sprinkler heads or spray irrigation equipments that could produce water droplets with a diameter of less than 4.00 mm and a sprinkler intensity less than or equal to that allowed by the soil.In the later stages of growth,it was suggested that sprinkler heads and spray irrigation devices with larger droplet sizes and sprinkler intensities greater than those allowed by the soil be used to achieve energy efficiency,low energy consumption,higher irrigation efficiency and irrigation assurance rates and efficient use of sprinkler water. |
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