Effects Of Film Mulched Drip Irrigation With Saline Water On Soil Environment And Cotton Growth

Because of water resources are extremely scarce in the Hebei Low Plain,carrying out the research on the safe irrigation technology for cotton with saline water has great significance to rationally exploit and utilize shallow underground water,as well as to alleviate regional freshwater resource shortage and ensure the sustainable development of the cotton industry.A field study on cotton was conducted at Hengshui,Hebei province during 2017-2019 growing season.Film mulched drip irrigation was used to apply water.Five salinity levels of irrigation water were set up:1,3,5,7 and 9 g/L.Distribution characteristics and migration law of soil water and salt in the cotton field were investigated.The responses of cotton growth and soil environment to saline water drip irrigation were explicated.The soil quality index?SQI?was used to evaluate the soil quality of cotton field,and the appropriate irrigation water salinity index was proposed.The main results were as follows:?1?Annual and interannual variation characteristics of soil water and salt in the drip-irrigated cotton field with saline water were studied.During a cotton growing period,soil moisture content and salinity increased with the increase in irrigation water salinity,especially for the soil salinity.The distribution characteristics of soil water and salt in soil profile were different at different periods,and the fluctuation range of soil water and salt decreased with the increase of soil depth.In wet years?2017 and 2018?,soil moisture was sufficient and salt content was relatively lower;while in drought year?2019?,soil moisture was low while soil salinity was high.The distribution of soil water and salt was uneven due to film mulching,the soil water and salt content under mulching row was higher than that under bare row.?2?The effects of drip irrigation using saline water on the cotton growth,seed cotton yield and fiber quality were revealed.During a cotton growing period,there were no significant differences among the 1,3,5 and 7 g/L irrigation treatments on the cotton emergence rate and yield,but the treatment of 9 g/L significantly decreased in 2017 and 2019.While in 2018,there were no significant differences occurred in cotton emergence rate and yield among treatments.Cotton yield variation among years mainly affected by meteorological factors and salinity levels of irrigation water.The salinity of test irrigation water had no significantly negative impact on cotton fiber quality.?3?The effects of saline water irrigation on evapotranspiration?ET?and water use efficiency?WUE?of cotton were investigated.Saline water drip irrigation had a certain degree of influence on ET of cotton,among which the ET at flowering stage was greatly affected by the salinity of irrigation water.There was no significant impact on ET when the irrigation water salinity was?5 g/L.The salinity of irrigation water had a few negative effects on WUE,and there were no significant differences among five treatments.?4?The effects of saline water drip irrigation on physico-chemical properties of soil plough layer were clarified.High salinity of irrigation water had a tendency to deteriorate the soil physico-chemical properties.Compared with 1 g/L treatment,the treatment of 7 g/L and 9g/L significantly increased soil EC_1:5,sodium adsorption ratio and bulk density,decreased soil porosity,saturated hydraulic conductivity and enzyme activity,and destroyed water stable aggregate.However,plastic film mulch improved the soil quality,the soil physico-chemical properties under mulching row was better than that under bare row.In our study,the SQI tended to decrease with the increase of irrigation water salinity,compared with 1 g/L treatment,the SQI of 3,5,7 and 9 g/L treatments decreased by 1.18%,10.48%,16.48%and23.73%.?5?Considering the soil water-salt dynamics,cotton growth response and soil quality security,the maximum salinity of irrigation water for drip irrigation was 5 g/L in the Hebei Low Plain.Drip irrigation with 7 g/L saline water had significantly negative impact on soil quality,although there was no significant reduction in cotton yield.Its utilization potential needs to be further evaluated.9 g/L saline water was not suitable for drip irrigation directly.