Winter Irrigation Effects On Soil Moisture,temperature And Salinity,and On Cotton Growth In Salinized Fields In Northern Xinjiang,China

Object:Cotton is the most important economic crop in Xinjiang,but soil salinization restricts the sustainable and healthy development of cotton industry Freeze-thaw action is a unique formation mechanism of soil salinization in Xinjiang during seasonal freeze-thaw period.Winter irrigation can affect the migration of soil water,heat and salt during freeze-thaw period,which is a widely adopted improvement measure to deal with soil salinization.At present,studies on the change characteristics of soil moisture,temperature and salinity over time in cotton fields with different salinity levels under different winter irrigation quotas,the influence of winter irrigation on the growth of cotton in the following year and the method for determining suitable winter irrigation quotas need to be further enriched.Methods:From October 2018 to October 2020,the controlled winter irrigation experiment in the non-growth period and the field experiment of cotton planting under mulch drip irrigation in the growth period were carried out of saline cotton field in northern Xinjiang.And three kinds of salt background values were set,which were 5.15,8.17 and 11.15 g·kg^-1 and marked mild salinization(S1),moderate salinization(S2)and severe salinization(S3),respectively.At the same time,three levels of winter irrigation rates were set,which were 0,3000,3600 and 4200 m³·hm^-2 and marked W0,W1,W2 and W3,respectively.Results:(1)Winter irrigation leaching can stabilize soil temperature and reduce soil freezing and thawing index.And the effect of winter irrigation on heat preservation increased with the increase of winter irrigation quota and salinization degree,and the effect of winter irrigation on freezing index and melting index of severe salinization test group was more significant.Winter irrigation can increase the surface water content of the soil in the freeze-thaw stage of cotton field and weaken the surface accumulation of soil salt.Winter irrigation has a more significant effect on salt storage and washing in soil of severely salinized cotton fields.When the quota of winter irrigation is more than 3600 m³·hm^-2,the water content in 0?100 cm soil layers of different salinized cotton fields can increase by more than 20%and the desalination can reach more than 40%.(2)Winter irrigation treatment affected cotton growth index and cotton fiber quality in the next year.And the response degree of cotton growth index to winter irrigation decreased with the increase of salinization degree.Winter irrigation had the greatest effect on stem diameter and the least effect on leaf area index of cotton in the next year.The effect of irrigation quota on uniformity index,breaking strength and elongation of saline cotton field in the following year was significantly weaker than that of the average length and micronaire value in the upper half,and the effect of winter irrigation on cotton fiber index in moderate and severe saline cotton fields was more significant.There was no significant difference in emergence rate and yield of mild and moderate saline cotton fields under the treatment of winter irrigation quota of 3600 m³·hm^-2 and 4200 m³·hm^-2(P>0.05).Seedling emergence rate and yield of severe salinization cotton fields increased significantly with the increase of winter irrigation quota.(3)When there was no control variable for simple correlation analysis,the winter irrigation quota and initial salt content were extremely significantly correlated with the distribution of water,heat and salt during freezing and thawing,and the emergence rate of cotton in the following year,seed cotton yield,and comprehensive benefit indicators(P<0.01).Except for the control variables of winter irrigation,i.e.winter irrigation quota and initial salt content,the net correlation among cotton seedling emergence rate,seed cotton yield and comprehensive benefit index in the next year still existed,and there was a significant correlation among cotton emergence rate,seed cotton yield,economic benefit and water productivity(P<0.05).Moreover,the winter irrigation treatment strengthens the multiple correlations among cotton seedling emergence rate,seed cotton yield and comprehensive benefit indicators.(4)Salinization level and winter irrigation quota of cotton field affect the harvest index,economic benefit and water productivity in the following year.And those indexes all decreased with the increase of initial salt content,and increased with the increase of winter irrigation quota.The effect of winter irrigation on the comprehensive index of salinized cotton field was economic benefit,water productivity and harvest index from strong to weak.The suitable winter irrigation quota for different objectives in different saline cotton fields increases with the increase of initial soil salt content.When the winter irrigation quota of mild,moderate and severe saline cotton fields were 3416.83?4256.14,4256.14?6502.96 and 6502.96?9614.24 m³·hm^-2,respectively,the cotton seedling emergence rate,seed cotton yield,harvest index,economic benefit and water productivity can reach more than 90%of the target maximum value at the same time.Conclusions:This study revealed the multiple correlation between the quota and initial salt content of winter irrigation and soil water,heat and salt in freezing and thawing period,cotton growth index in the next year and its comprehensive benefit index could be strengthened by controlled winter irrigation.Winter irrigation can provide a good growth environment for crops,improve harvest index,economic benefits and water productivity.However,the suitable winter irrigation quota for cotton fields with different salinization degree is different according to different benefit indexes.