Distribution Characteristics Of Water Salt And Fertilizer In Fields Drip Irrigation Under Mulched And Its Influence On Cotton Growth

Due to the effect of special natural environment and climatic characteristics,northwest China,especially Xinjiang,has wide distribution of saline-alkali land,resulting in low efficiency in the use of farmland water and fertilizer.This thesis employed Geo-statistical method,Grey relational analysis（GRA）,path analysis method and Grey predicting model GM（1,1）to study the effects of water,salt and fertilizer on cotton growth in Xinjiang cotton fields drip irrigation under mulched in order to improve the utilization ratio of water and land resources and provide guidance to establish scientific and reasonable irrigation and fertilization systems.Also,the findings of the study were expected to provide theoretical suggestions and practical references for coping with climate change and thus effectively avoiding climate risks in the process of cotton production.The main conclusions are as follows:（1）The variation of soil particle composition in Baotou Lake irrigation area is weak in silt,moderate in clay and sand,as indicated by C_v value:sand>clay>silt.The spatial correlation degree of soil bulk density at the depth of 0-20 cm and 20-40 cm showed moderate spatial correlation,while other models displayed strong spatial correlation;the spatial correlation degree of the exponential model at the depth of 40-60 cm indicated moderate spatial correlation,other models reported strong spatial correlation.The spatial correlation degree of soil water content,salinity and nutrient content all displayed moderate spatial correlation.（2）On the basis of ensuring the emergence of seedlings,it was generally shown that soil water content plays a major role in cotton yield.Months ranging from May to August were observed to have higher correlation with the cotton yield.In the meanwhile,August and September were found that salt content had a greater impact on cotton yield.But there was certain variation in the degree of influence of water,salt and fertilizers on cotton production in different years.In addition,the nitrogen content in July and phosphorus content of soil in August had the largest positive direct effect on cotton yield,and soil salt content in May and August had the largest negative direct effect on cotton yield.（3）The Logistic growth model was used to analyze the variation characteristics of cotton relative plant height（R_H）,relative leaf area index(R_LAI),and relative dry matter accumulation（R_D）as growing degree days(P_GDD)change.It was found that when the growing degree days reached about 793℃,1150℃,and 1300℃,the growth rate of cotton R_H,R_LAI and R_D increased to the maximum value respectively.In the early stage of cotton growth,that is when P_GDD was less than about 900℃,the change rate of R_H and R_LAI was greater than that of R_D.While in the later stage of growth,that is when P_GDD was greater than about 900°C,the result was opposite to that in the early stage.（4）A model of drip irrigation under mulched water-fertilizer coupling and cotton yield suitable for arid,semi-arid regions and temperate continental climate conditions was established.When the water consumption lied between 472.52 and 754.61 mm,the irrigation volume ranged from 343.58 to 675.61 mm,and the fertilizer rate was between 108.82 and 700.16 kg/ha,the theoretical cotton yield reached 5189.90 kg/ha to 7839.60 kg/ha.Among the meteorological factors in different cotton areas,the average air pressure（AAP）,average maximum temperature（MAXT）,sunshine duration（SD）,average temperature（AT）,and average relative humidity（ARH）were highly correlated with cotton yield,and had a greater impact on cotton yield,while rainfall（RF）and average minimum temperature（MINT）had a smaller impact on cotton yield.Monthly analysis results showed that the AAP in April,May,and October had a higher correlation with cotton production;in April,May,September,and October,the MAXT was highly correlated with cotton production;with regard to the high correlation between SD and cotton production,April,July,September and October reached the top four;in April,May,June and July,there was a high correlation observed between ARH and cotton production.While the months with high correlation between RF,MINT and cotton production were in June,July and August.