Study On The Optimal Regulated Deficit Irrigation And Fertilization System Of Drip Irrigation Jujube In Arid Oasis Area

In response to the severe water shortage and high potassium fertilizer consumption in agricultural production in Xinjiang,a 6-year field experiment on irrigation and fertilization of jujube trees from 2016-2021 was conducted at the forestry fruit industry experimental site of Xinjiang Agricultural University in Team 10,Hongqipo,Aksu Prefecture,Xinjiang.In particular,the jujube tree is the featured fruit tree of Xinjiang.Based on the fixed-position observation using advanced equipment such as a large-scale weighing evapotranspiration meter and a photosynthesis meter,a systematic study on water consumption,physiology,yield and quality of jujube trees was conducted.The water deficit compensation mechanism of jujube trees was revealed.The water-nutrient-yield-quality response relationship of jujube trees was clarified.The reliability of three evapotranspiration estimation models in jujube trees with drip irrigation in arid zone was verified.The applicability of three CWSI models in the diagnosis of water deficit of jujube trees was evaluated.Based on the thorough investigation of the composition of production factors,a comprehensive efficiency evaluation system for jujube trees was constructed.（1）Under the same fertilizer application,mild（75%ET_c）and severe（50%ET_c）water deficit significantly reduced evapotranspiration of jujube trees by 4.75%-5.24%and 16.27%-18.54%,respectively.Under the same irrigation quota,reduced potassium fertilizer application（50%K₂O）resulted in a 2.73%-3.58%reduction in evapotranspiration of jujube trees,whilst increased potassium fertilizer application（150%K₂O）had no significant effect on evapotranspiration（P>0.05）.Therefore,the effect of water deficit on jujube trees was significantly higher than that of fertilizer application.Fertilizer tends to indirectly affect evapotranspiration of jujube trees by affecting plant physiological development.（2）Water deficit applied at the flowering and young fruit stages had significantly lower effects on SPAD values,net photosynthetic rate and transpiration rate of leaves sensitive to water changes than at the fruit expansion stage（P<0.05）.The application of water deficit during the flowering and young fruit stages was beneficial in reducing growth redundancy（e.g.,a decrease of 4.03%-14.55%in the growth of fruit-bearing shoots and 10.95%-26.17%in plant height）.The fruit expansion stage is a critical water demand period for fruit trees,and the application of mild（75%ET_c）and severe（50%ET_c）water deficits significantly reduced the net photosynthetic rate by 7.98%and 21.75%during this reproductive period,respectively.The rehydration after water deficit could repair the damage to plants caused by water deficit;with a longer duration,it exhibited larger repair effects on water-sensitive indicators,whilst the effects on water-insensitive indicators were not significant.（3）Increased application of potassium fertilizer significantly increased SPAD,net photosynthetic rate and transpiration rate of the leaves（P<0.05）but had no significant effect on other physiological indicators.In contrast,due to insufficient nutrient supply to plant organs,reduced application of potassium fertilizer significantly reduced leaf area index,the length of fruit-bearing shoots and stem diameter by 4.02%,10.42%and 14.59%,respectively.（4）At the flowering and young fruit stage,mild and severe water deficits could increase total sugar content by 5.49%and 10.28%,and jujube fruit volume by 3.40%and 5.06%,while reducing jujube yield by 4.22%and 11.36%,respectively.In contrast,water deficit at the fruit expansion stage caused a decrease in fruit volume by 0.74%～12.80%and in fruit yield by 3.96%～15.96%.This was detrimental to improving economic efficiency.Under adequate irrigation and mild water deficit conditions,increased potassium fertilizer application increased total sugar content by 2.28%and 9.29%,fruit volume by 2.47%and 4.42%,and jujube yield by 3.01%and 6.10%,respectively;reduced potassium fertilizer application reduced total sugar content by 3.57%and 19.55%,fruit volume by 7.51%and 8.12%,and yield by 5.42%and 9.37%,respectively.Under severe water deficit conditions,increased or reduced potassium fertilization caused significant decreases in total sugar content,fruit volume and jujube yield（P<0.05）.（5）A comprehensive benefit evaluation system of irrigation and fertilization system for jujube trees was constructed.The entropy weight-TOPSIS method,the hierarchical grey relational analysis method and the principal component analysis method were compared.The results show that the principal component analysis method exhibited high objectivity and could avoid the influence of multicollinearity,with low inter-annual stability.The entropy weight-TOPSIS method was more reasonable for ranking the treatments with high objectivity.However,it was susceptible to the influence of some extreme values and had intermediate inter-annual stability.The hierarchical grey relational analysis method showed the highest inter-annual stability and reasonable ranking for each treatment,while it required expert scoring in a decision aid.With comprehensive consideration,the hierarchical grey relational analysis method was recommended for comprehensive benefit evaluation.（6）B Based on the hierarchical grey relational analysis method,the optimal treatments were determined as high fertilizer application+adequate irrigation and high/medium fertilizer application+mild water deficit.However,additional application of potassium fertilizer is likely to cause soil fertilizer residues.Thus,in this study,the irrigation and fertilization system of medium fertilizer application+mild water deficit was recommended,i.e.,irrigation scheduling（100%ET_cat the budding stage and 75%ET_cfrom the flowering stage to the fruit expansion stage）;fertilization system（basal application of 200 kg/ha compound fertilizer（N-P₂O₅-K₂O,17-17-17,total nutrients≥51%）;120 kg/ha potassium fertilizer（K₂O）at the flowering,young fruit and fruit expansion stages,total nutrients≥52%）.（7）The applicability of theoretical,empirical and semi-empirical semi-theoretical crop water stress index（CWSI）models（i.e.,CWSI-T1,CWSI-E and CWSI-T2）was evaluated for water stress diagnosis of jujube trees with drip irrigation in the arid oasis areas.The results show that the three CWSI models showed similar stability and significant responses to the water deficit of jujube trees.CWSI-T2 showed the best performance in reflecting parameters such as soil water stress index,soil water content and stomatal conductance,followed by the CWSI-E and the CWSI-T1.Therefore,the order of preference for the three CWSI models is CWSI-T2>CWSI-E>CWSI-T1.（8）The applicability of Shuttleworth-Wallace（S-W）,Dual Crop Coefficient Approach（Dual K_c）and Priestley-Taylor（P-T）models in estimating evapotranspiration of jujube trees with drip irrigation in arid oasis areas was demonstrated.According to the results,the S-W model exhibited medium simulation errors（RMSE=0.74-0.94 mm/d）;the simulation results were easily affected by plant height,soil moisture,temperature and net radiation;the model was generally evaluated as‘good’.The Dual K_cmodel showed basal crop coefficients of 0.4,1.0 and 0.5,respectively;the model error was minimal（RMSE=0.60-0.82mm/d）;the model was generally evaluated as‘excellent’.The P-T model exhibited the largest simulation error（RMSE=0.77-0.97 mm/d）and was generally evaluated as‘unacceptable’.When the parameterαin the model was improved,the overall evaluation of the model was improved to‘excellent’（RMSE=0.67-0.88mm/d）.However,the simulation results were easily affected by net radiation and temperature changes.Therefore,this study suggests using the Dual K_cmodel to estimate the evapotranspiration of jujube trees in arid areas.