| As a large agricultural country,drought and low utilization efficiency of water and fertilizer limit the development of agriculture in China.γ-PGA is a potential soil amendment,which can improve the physical and chemical properties of soil,promote crop growth and increase crop yield.In view of the shortage of water resources and the low utilization efficiency of water and fertilizer,a pot experiment was set up in this study.The effects of γ-PGA application on soil water,heat,fertilizer and soybean growth and physiological characteristics and yield under different irrigation methods,irrigation amount and nitrogen application rate were analyzed.The effects ofγ-PGA water and nitrogen coupling on soybean yield under drip irrigation were analyzed by establishing a ternary quadratic regression equation based on experimental data.The optimal γPGA water and nitrogen application rate suitable for soybean growth was evaluated by entropy weight-TOPSIS comprehensive evaluation model.The main research results are as follows:(1)The effects of γ-PGA application on soil moisture content,temperature,nitrate nitrogen,available potassium and available phosphorus under drip irrigation and conventional irrigation were analyzed.The average soil moisture content of drip irrigation treatment with different γPGA application amounts increased by 1.35%-11.68%compared with that of conventional irrigation.Under different irrigation methods,the soil moisture content of γ-PGA treatment increased compared with that of non-γ-PGA treatment,and the soil moisture content increased first and then decreased with the increase of γ-PGA application amount.The soil temperature of drip irrigation treatment was higher than that of conventional irrigation at 5 cm,15 cm and 25 cm soil layers,and the temperature difference of lower soil was higher than that of upper soil.The application of γ-PGA treatment was beneficial to soil warming,but excessive application of γPGA would reduce soil permeability and temperature flux.The content of soil nitrate nitrogen and available phosphorus is:drip irrigation>conventional irrigation,soil available potassium:drip irrigation<conventional irrigation,under the same irrigation method,soil nutrient content is positively correlated with the amount of γ-PGA application,and the application of γ-PGA treatment can increase soil nutrient content.(2)The effects of γ-PGA application rate on soybean growth physiological characteristics and yield under drip irrigation and conventional irrigation were revealed.Compared with conventional irrigation,drip irrigation can effectively promote the plant height,leaf area index,aboveground dry matter,yield,photosynthetic characteristics and water use efficiency of soybean.The yield of soybean treated with 0.3%γ-PGA was the best,and the yield of drip irrigation and conventional irrigation was 3612.27 kg/ha and 3408 kg/ha,respectively.Under drip irrigation,the yield of γ-PGA treatment increased by 5.31%-12.88%compared with that of no treatment.Under conventional irrigation,the yield of γ-PGA treatment increased by 3.23%-12.26%compared with that of no treatment.(3)The effects of γ-PGA application on soil moisture content,temperature,nitrate nitrogen,available potassium and available phosphorus under different drip irrigation methods were clarified.Under different treatment conditions,soil moisture content was positively correlated with the amount of γ-PGA applied.When the amount of irrigation and nitrogen application was low,the amount of γ-PGA application inhibited soil temperature and increased the amount of irrigation and nitrogen application.Soil temperature was positively correlated with the amount of γ-PGA application.γ-PGA showed double effects of warming and cooling in different soil layers under the same treatment.Compared with the control group,the contents of nitrate nitrogen,available potassium and available phosphorus in the soil treated with γ-PGA were increased.(4)The effects of different irrigation amount and nitrogen application amount on the growth physiological characteristics and yield of soybean were clarified.Under different irrigation treatments,the plant height of soybean treated with 0.3%γ-PGA was larger.Under different nitrogen application treatments,the plant height of soybean was positively correlated with the amount of γ-PGA applied,and the leaf area index of soybean was positively correlated with the amount of γ-PGA applied.The soybean yield and water use efficiency were the best when the irrigation amount was 4425 m3/ha and the γ-PGA application amount was 0.3%,which were 3612.27 kg/ha and 0.83 kg/m3,respectively.The yield and water use efficiency of soybean were the best when the nitrogen application rate was 252 kg/ha and 0.3%γ-PGA application rate was 3717.04 kg/ha and 0.85 kg/m3,respectively.(5)The water-nitrogen coupling regression model of γ-PGA was established,and the equation was verified.The influence of each factor was as follows:γ-PGA application amount>nitrogen application amount>irrigation amount.Through double effect analysis,γ-PGA water and water-nitrogen coupling were synergistic effects,and γ-PGA water synergistic effect>waternitrogen synergistic effect,γ-PGA nitrogen coupling was antagonistic response.The relationship between γ-PGA application amount,irrigation amount,nitrogen application amount and soybean yield was parabolic.Through calculation,the soybean yield was 3400-3800 kg/ha,the application amount of γ-PGA was 0.268%-0.332%,the irrigation amount was 4363.35 m3/ha4711.8 m3/ha,and the nitrogen application amount was 130.43 kg/ha-205.57 kg/ha.(6)The analysis of entropy weight-TOPSIS comprehensive evaluation model showed that the comprehensive effect was the best when γ-PGA application amount was 0.3%,irrigation amount was 4425 m3/ha and nitrogen application amount was 252 kg/ha under drip irrigation. |
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