Optimization And Regulation Of Irrigation System For Urban Green Turfgrass Based On Warer Balance

Urban turfgrass is an important type of urban ecological landscape,and the water balance of turfgrass is an significant part of urban ecohydrological processes.In arid and semi-arid areas,the severe scarcity of water resources and the unreasonable irrigation of lawns have led to a huge contradiction between supply and demand of urban water resources.At present,the irrigation management level of urban turfgrass in China is generally low,while the reasonable utilization rate of urban water resources is low,thus the problem of improving the irrigation management level of urban turfgrass and the effective use of water resources needs to be solved.Therefore,it is of great practical significance to optimize the irrigation system of urban turfgrass to alleviate the contradiction between water supply and demand and to improve the efficiency of water resources utilization.This study took Poa pratensis turf in Zhangjiakou area as the research object,and carried out a detailed study by coupling lawn field experiment and agricultural model simulation.The characteristics of turfgrass water balance were analyzed based on field test data.The applicability of root zone water quality model（RZWQM2）to turfgrass in Zhangjiakou,Hebei province was investigated using field test data.Based on the water balance principle,RZWQM2 model was used to simulate soil water content,turfgrass evapotranspiration and cumulative leakage under different irrigation systems.The responses of soil water content,evapotranspiration and cumulative seepage to different irrigation systems were analyzed.The optimal irrigation system for urban lawn in Zhangjiakou area of Hebei province was studied,which provided theoretical basis for the efficient utilization of urban water resources in this area.The main conclusions are as follows:（1）The average soil water content of turfgrass under 0-40 cm soil layer in2020-2021 was 23.24%and 23.27%in the growing season（from mid-April to mid-October）,and 19.70%in the 40-60 cm soil layer in 2020.In 2021,the average soil water content under 40-70 cm soil layer is 20.39%,and the soil water content under 60-100 cm soil layer is basically saturated.（2）The annual and ten-day evapotranspiration of Poa pratensis turf during2020-2021 presented a single-peak curve,which increased first and then decreased.In 2020 and 2021,the annual evapotranspiration of turfgrass was larger from May to September,accounting for 75.34%and 72.80%of the annual total evapotranspiration,respectively.The daily evapotranspiration reached the maximum in early July and early June,with the maximum of 9.15 mm/d and 7.01 mm/d,respectively.The average evapotranspiration reached the maximum in late May and mid-June,and the maximum evapotranspiration was 6.44 mm/d and 5.26 mm/d,respectively.（3）The daily water leakage of Poa pratensis turf in 2020-2021 changed with the change of rainfall and irrigation.The cumulative water leakage was 232.74 mm and332.64 mm,respectively,and the water leakage mainly occurred in the growth period（May-October）.The daily water leakage reached the maximum on July 8 and October 15,respectively,with the maximum value of 7.35 mm and 5.30 mm.（4）The simulation results of RZWQM2 model on soil water content and monthly evapotranspiration were better in the rate period and validation period.The simulated d values of soil water content at 40 cm,60 cm and 80 cm were 0.95,0.94 and 0.99,respectively.The simulated d values of soil water content at the validation stage were0.98,0.99 and 0.97,respectively.The simulated RMSE（Root Mean Square Error）values of soil water content at the depth of 20-80 cm ranged from 0.56%to 2.27%.The MRE（Mean Relative Error）values ranged from 1.48%to 8.33%,and the MRE values were less than 10.00%in both validation and rate period.The RMSE and MRE values of monthly evapotranspiration in the validation period and validation period were 22.08 mm and 12.60 mm,and 15.22%and 9.94%,respectively,with d values greater than 0.90.The results show that RZWQM2 model has good applicability in Zhangjiakou of Hebei province.（5）The simulation analysis of soil water content,total evapotranspiration and cumulative leakage in 0-100 cm soil layer of Poa pratensis turf during the peak growth period（May to October）in 2021 showed that the average soil water content in T_80%-21 and T_80%-18treatments was only 0.70%and 0.63%lower than that in T_100%-12（Irrigation volume 29.60 mm）treatment under full irrigation,49.75mm and44.75mm water resources are saved respectively.Therefore,T_80%-18（Irrigation volume15.78 mm）and T_80%-21（Irrigation volume 13.53 mm）irrigation treatments were better than other treatments under 80%irrigation conditions.The overall trend of evapotranspiration was as follows:irrigation times 18>15>12>21.The total evapotranspiration under T_80%-15（Irrigation volume 18.94 mm）,T_80%-18and T_80%-21irrigation treatment decreased less than the total evapotranspiration under 100%full irrigation.Therefore,the irrigation treatment of T_80%-15,T_80%-18 and T_80%-21 was superior to other irrigation treatments.The simulated cumulative total leakage of T_80%-18 and T_80%-21 irrigation treatments was 144.31 mm and 144.95 mm,respectively.The cumulative total leakage of T_80%-18 irrigation treatment was lower than that of T_80%-21 irrigation treatment.In general,T_80%-18irrigation treatment was the optimal irrigation system for lawn in Zhangjiakou area.