Response Of Pumpkin To Water Deficit And Optimization Of Irrigation Schedule With Drip Irrigation Under Mulch In The Hexi Oasis

In the cold and arid region of Hexi Oasis,ecological degradation,water shortage and the traditional irrigation mode of diffuse irrigation had become the main factors limiting the sustainable development of agriculture.At present,the development of water-saving agriculture,enhance the efficiency of agricultural water use,improve the quality and efficiency of agriculture,and ensure food security immediately.Widely planted in the area,pumpkin is a drought-tolerant cash crop with great nutritional value and commercial advantages that has good potential for water conservation.In this study,pumpkin soil physical and chemical index characteristics,photosynthetic characteristics,and growth dynamic characteristics were examined under the water regulation deficit of drip irrigation under mulch,and it was discovered how to save water,stabilize the yield,and improve the quality of the pumpkin under this condition in the Hexi Oasis.Three water gradients were set up in the experiment,namely adequate irrigation（75%～85%FC）,light water deficit（65%～75%FC）,and moderate water deficit（55%～65%FC）.There were eight water deficit treatments:light water deficit at seedling stage（LFFF）,light water deficit at vine extension stage（FLFF）,light water deficit at fruit expansion stage（FFLF）,light water deficit at maturation stage（FFFL）,moderate water deficit at seedling stage（MFFF）,moderate water deficit at vine extension stage（FMFF）,moderate water deficit at fruit expansion stage（FFMF）,moderate water deficit at maturation stage（FFFM）and one fully irrigated control treatment（CK）.The main findings of the study were as follows:（1）The drip irrigation under mulch has an obvious effect of increasing temperature and preserving moisture,effectively regulating the water and heat environment in the root zone,and the water deficit can obviously increase soil temperature,which is beneficial to crop growth and development.Pumpkin soil moisture primarily changes in the 0-60 cm soil layer,with the fruit expansion and seedling stages showing the most dramatic trends in soil moisture change.The consumption of soil fast-acting potassium was the highest,followed by alkaline nitrogen and fast-acting phosphorus during the whole growth stage of pumpkin,and the consumption of soil nutrients by the crop was significantly inhibited by moderate water deficit.Water deficit suppressed the number of bacteria and actinomycetes in the soil,but increased the number of fungi and decreased with increasing depth of the soil layer.Light water deficit treatment increased soil urease and sucrase activities,but moderate water deficit exhibited inhibition of soil urease and sucrase activities,while water deficit increased soil catalase and phosphatase activities.（2）The water deficit treatments affected differently the photosynthetic characteristics of pumpkin,compared with the control CK,the net photosynthetic rate decreased from 0.91%to 17.67%（2020）and 3.01%to 17.25%（2021）,transpiration rate decreased from 2.51%to 17.25%（2020）and 3.57 to 16.95%（2021）,stomatal conductance decreased from 1.10%～21.72%（2020）and 0.98%～19.86%（2021）,while the increase in intercellular CO₂ concentration was 1.11%～18.20%（2020）and1.77%～20.11%（2021）.Compared to the control CK,the water deficit treatments increased the root to crown ratio of pumpkin（3.31%～24.23%,2020;2.97%～24.31%,2021）while decreasing the vine length（0.92%～9.85%,2020;1.14%～9.36%,2021）,stem thickness（2.48%～11.24%,2020;2.23%～12.34%,2021）,and leaf area index（1.08%～12.51%,2020;1.02%～12.02%,2021）.Dry matter accumulation per plant was significantly reduced by 5.97%to 20.32%（2020）and 4.22%to 21.79%（2021）except for LFFF（615.10 g,2020;667.34 g,2021）and FFFL（597.62 g,2020;649.13 g,2021）,which were not significantly different from CK.（3）The fully irrigated treatment had the maximum water consumption for the entire fertile period（2020:404.97mm;2021:411.86mm）,and in each water deficit treatment,it reduced by 8.94%to 24.61%（2020）and 7.81%to 22.78%（2021）.The water consumption,daily water consumption intensity and water consumption modulus showed an increasing and then decreasing trend with the advancement of the growth stage,in which the fruit expansion and vine extension stages were the critical periods of crop water demand.The water deficit treatment reduced pumpkin yield index,and there were no significant effect of light water deficit treatments pumpkin yield and components at seedling and maturation stages with control CK,where LFFF had the highest water use efficiency of 12.37 kg·m^-3（2020）,12.57 kg·m^-3（2021）and yield of45066.90 kg·hm^-2（2020）,46866.90 kg·hm^-2（2021）and FFFL water use efficiency was12.04 kg·m^-3（2020）and 12.52 kg·m^-3（2021）with yields of 43900.22 kg·hm^-2（2020）and 45733.56 kg·hm^-2（2021）.（4）Water deficit during the nutritional growth stage of pumpkin had no discernible impact on quality,however water deficit during the reproductive growth stage increased the quantity of soluble sugar,protein,vitamin C,and soluble solids while lowering the content of starch.A comprehensive principal component evaluation score ranked treatment FFFL as having the best fruit quality,LFFF as having the second-best fruit quality and FLFF as having the worst fruit quality.（5）In the Hexi Oasis,the Stewart model（R²=0.7873）provided the best water production function model for the conditions of drip irrigation under mulch regulatory deficiency.The results of an evaluation of pumpkin yield,quality,fertility water consumption,water use efficiency,and soil nutrient consumption using the entropy-weighted TOPSIS method showed that the best irrigation strategy for pumpkin under drip irrigation in the Hexi Oasis was the treatment of light water deficit at maturation stage and adequate irrigation at other growth stages.