| Agriculture is the foundation of China's national economy.But at the same time,China is faced with shortage of water and arable land resources,so the water-saving irrigation and use of saline-alkali land are important issues in China's agricultural development.In recent years,with continuous increase in consumption of chemical fertilizers,the non-point source pollution has occurred frequently.The reasonable solution for management of water,salt and fertilizers has become one of the important ways of maintaining sustainable agricultural development.In this paper,the cotton as a cash crop was used as the research object.The indoor soil-column experiment was conducted based on the design of two factors and three levels.The soil salt content was set at three levels:non-salinized soil,mildly-salinized soil and moderately salinized soil,respectively represented as F,Q and N,The pure nitrogen application amount was also set at three levels:0 Kg hm-2,150 Kg hm-2 and 300 Kg hm-2,respectively represented as N0,N1 and N2.In total,there were nine treatments.The pot experiment was designed using the "3414"scheme;specifically,the experiment was based on three factors of nitrogen(N),salt(S)and water(W),each of which was set at four levels.In total,there were 14 treatments.The irrigation quotas were 105,140,175 and 210m3/mu respectively,which were represented as W0,W1,W2 and W3 respectively.The amount of nitrogen fertilizer(pure nitrogen)applied was 0,150,300 and 450 kg·hm-2 respectively,which were represented as N0,N1,N2,and N3 respectively.Salinized soil was classified into four kinds:non-salinized soil,mildly-salinized soil,moderately-salinized soil and severely-salinized soil,which were represented as S0,S1,S2 and S3 respectively.Through the combination of indoor experiments and potted tests,this experiment is designed to study the movement rules of soil water,salt,nitrogen and ions in the mulched drip irrigation under different water-salt-nitrogen conditions and explore the response of physiological-ecological indices of cotton to water,salt and nitrogen.In addition,the quadratic regression model with three factors(water,salt and nitrogen),Jensen model and AquaCrop crop growth model were used to simulate the experimental results.Based on the model prediction,the optimal irrigation and fertilization solution for planting cotton in soils with different salt stress was presented.The main research results are as follows:(1)Under the condition of water infiltration,the salt and nitrogen coupling showed a certain synergistic effect in terms of water infiltration,water redistribution,soil water content,salt movement and nitrogen transport.In the high-salinity high-nitrogen(ZN2)treatment and low-salinity moderate-nitrogen(FN1)treatment,the proportion of ammonium nitrogen converted to nitrate nitrogen was 63.21%and 47.41%respectively,reaching a considerably high value.In the moderate-salinity high-nitrogen treatment(QN2),the conversion proportion of ammonium nitrogen was 11.04%.(2)The effects of experimental variables on the average soil water content and average soil salt content were sorted from the largest to the smallest:soil salt content>irrigation amount>nitrogen application amount.The soil salt content had a significantly positive correlation with each ion.The effects of various ions on soil salt content were sorted from the largest to the smallest:chloride ions>magnesium ions>sodium ions>calcium ions>potassium ions.The nitrate nitrogen in the soil had a significantly negative correlation with soil salt content.When the soil salt content increased,it decreased basically;when the irrigation amount increased,it decreased directly;when the nitrogen application amount increased,it first decreased and then increased and finally decreased again.(3)Under the condition of mulched drip irrigation,the water,salt and nitrogen had a greater impact on the ecological indicators of cotton at seedling stage and bud stage;moreover the soil salt content was the main factor constraining cotton yield.The leaf area index of cotton could more accurately characterize the cotton yield and its growth status;the leaf temperature and stomatal conductance had a significant effect on cotton growth indexes.In the experimental programs,the treatment with the highest yield was 12#N1S1W2,and the smallest treatment was 8#N2S2W0.The cotton yield of 12#was higher than that of 8#,increasing by 172.00%.(4)The formula of quadratic regression model with three factors(water,salt and nitrogen)is Y=264.723-72.444N-111.158S+145.533W-53.276N2+42.732S2+34.802W2+129.537NS-93.775N W-43.447SW.The effects of water,salt and nitrogen on cotton yield were sorted from the largest to smallest:irrigation amount>soil salt content>Interaction between nitrogen and salt>nitrogen application amount>interaction between water and nitrogen>interaction between water and salt.The optimal water-salt-fertilizer coupling range was as follows:irrigation amount:173,184)(m3/mu);nitrogen application amount:202(kg·hm-2);soil salt amount(2.46,3.37)(g kg-1).(5)The simulated effects of three models were sorted from the largest to smallest:quadratic regression model with three factors(water,salt and nitrogen)>AquaCrop model>Jensen model.The AquaCrop model was used to predict 64 experimental treatments.The simulation result showed that the treatment with the largest predicted yield(7.068 t hm-2)was N1S1W3.The optimal irrigation and fertilization solution for non-salinized soil was N2S0W3;the optimal irrigation and fertilization solution for mildly-salinized soil was N1S1W3;the optimal irrigation and fertilization solution for moderately-salinized soil were N0S2W3 and N2S2W3;the optimal irrigation and fertilization solution for severely-salinized soil was N2S3W3.The research results preliminarily reveal the coupling effect of water,salt and fertilizers,providing references for optimization of irrigation and fertilization system in the cotton field with mulched drip irrigation and saline-alkali soil and playing a guiding role in reducing the non-point source pollution in irrigation and improving the water and fertilizer use efficiency. |
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