Effects Of Saline Water Irrigation On Soil Environment And Summer Maize Yield

Under the condition that the North China Plain is extremely short of freshwater resources,and the storge of saline water is abundant,it is of great significance to carry out the research on the safe irrigation technology for the rational development and utilization of underground saline water,to alleviate the shortage of fresh water resources and ensuring the sustainable development of agriculture.Based on the long-term saline water irrigation experiment starting in 2006,four salinity levels of irrigation water were tested:2 g/L（T1）,4 g/L（T2）,6 g/L（T3）,and 8 g/L（T4）,and fresh groundwater（1 g/L）was used as control treatment（CK）.The saline water of T1 to T4 was prepared by mixing sea salt into the freshwater.The distribution and variation of soil salinity in summer maize field in the 13th and 14th year of continuous saline water irrigation with different salinity were studied.The effects of saline water irrigation on soil physico-chemical properties and enzyme activity were clarified.The responses of summer maize yield and yield components to saline water irrigation were explored.Based on the minimum data set selected by principal component analysis,the soil quality index was calculated,and then the soil quality under saline water irrigation was evaluated.The main results were showed as follows:（1）The variation of soil salinity in summer maize field was proved.The distribution characteristics and variation process of soil salinity in summer maize field irrigated with saline water were affected by irrigation,rainfall,evaporation and transpiration.In the same maize growth season,soil salinity increased with the increase of irrigation water salinity,while decreased with the increase of soil depth,increasing first and then decreasing with the advancement of summer maize growth process.The distribution characteristics of soil salinity in different periods were quite different.At jointing stage,the soil salt content of each irrigation treatment was high,and the difference was significant.During the filling stage,the soil salt content of each treatment decreased,the differences among treatments decreased,and the peak of salinity value decreased.The average salt content in 0-100 cm soil layer of each treatment at maturity stage was relatively small compared with that at filling stage,while the salt content in 0-20 cm soil layer was higher.There were significant differences in soil salinity among different treatments.Because of less rainfall and twice irrigation in the maize growth season in 2019,the soil salinity of all treatments during the growth period of summer maize was higher than that in the same period in 2018.Compared with that before sowing,the soil salinity of all treatments decreased.（2）The effects of saline water irrigation on physical and chemical properties and enzyme activity of farmland topsoil was revealed.In the same year,EC_1:5,p H and SAR of topsoil in summer maize field increased with the increase of irrigation water salinity,while soil organic carbon content decreased.Saline water irrigation can destroy the soil structure of arable layer.With the increase of irrigation water salinity,soil bulk density increased,while porosity and water stable aggregate stability decreased.Moreover,the activity of catalase,urease and alkaline phosphatase were inhibited by saline water irrigation of high salinity.Compared with 2018,during the growth period of Summer maize in 2019,there was less rainfall and more irrigation,and the water and soil salt content were higher,resulting in a more seriously negative impact on the soil environment.Based on the two-year data,when the salinity of irrigation water was higher than 4 g/L,the physical and chemical indicators of soil were significantly worse than those of CK.（3）The response characteristics of summer maize yield and yield components to saline water irrigation with different salinity were clarified.In the same year,compared with fresh water irrigation,irrigation with appropriate salinity（2 g/L）had no significant effect on the number of productive ear,grain number per spike,100-grains weight and yield of summer maize.However,when the irrigation salinity was≥4 g/L,the yield components and yield of summer maize decreased significantly.Compared with 2018,the yield components and grain yield of maize in each treatment decreased significantly in 2019.Among them,the grain yield of CK,T1,T2,T3 and T4 treatments decreased by 14.2%,14.1%,15.5%,49.8%and 55.2%,respectively.（4）The soil quality evaluation method of saline water irrigation field was discussed.The principal component analysis was used to take the summer maize yield as the management objective,and finally the minimum data set in this study included four indicators:EC_1:5,SOC,S-ALP andρ_b.Based on the minimum data set,the soil quality index was calculated.And the results showed that saline water irrigation reduced the soil quality.Compared with CK,the soil quality index of T1,T2,T3 and T4 treatments decreased by 4.9%、19.7%、27.6%and 37.3%respectively.（5）Based on the comprehensive consideration of soil salinity variation,soil physical and chemical index,maize yield and soil quality index,the results showed that saline water≤2 g/L could be directly irrigated for summer maize in the study area.Irrigation with saline water≥4 g/L resulted in a significant increase in soil salinity and a significant decrease in soil quality index and summer maize yield,which was not recommended for irrigation.From the perspective of sustainable development,it is recommended that the salinity threshold of summer maize irrigation in the study area is 2 g/L.