Effects Of Saline Water Irrigation With Different Ionic Composition On Physical And Chemical Properties Of Potting Soil And Growth Of Lettuce

The development and utilization of brackish water and salt water resources is one of the important ways to alleviate the shortage of fresh water resources in agricultural production.But,salt stress caused by brackish water and salt water irrigation will affect the physical and chemical properties of soil and the physiological growth of crops.In order to explore the effects of different saline water quality on soil hydraulic properties and crop growth,a two-season pot experiment was carried out for cropping lettuce in the solar greenhouse.Taking the saturated solution of Ca SO₄as the control（CK+）,different chlorides were added to deionized water to form three saline water treatments with different cationic compositions（Na⁺,T1,T4 and T7;Na⁺/K⁺of 1:1,T2,T5 and T8;K⁺,T3,T6 and T9）but the same electrical conductivity.The soil bulk density,water holding properties,water and salt transport and lettuce growth were studied,and the feasibility and applicability of using Cation Ratio of Soil Structure Stability（CROSS）instead of Sodium Adsorption Ratio（SAR）to evaluate the impact of irrigation water quality on soil structure were analyzed.The purpose of this study is to provide scientific basis for the utilization of saline water to save fresh water resources and promote the sustainable development of irrigated agriculture.The main findings are as follows:The results showed that compared with CK+,saline water irrigation increased soil bulk density,reduced soil porosity and saturated hydraulic conductivity.With continuous irrigation of saline water,soil pore size distribution was significantly altered,and more micropores were formed,resulting in the improved water holding capacity of soils,namely the reduced soil infiltration performance.The most significant effect was observed in CK-.Both sodium absorption ratio（SAR）and cation ratio of soil structural stability（CROSS）showed the negative correlations with soil saturation hydraulic conductivity and the soil entry value parameters（α）.Compared with SAR,CROSS could better reflect the potential changes in soil physical properties caused by the changes in ionic compositions of irrigation water.The water distribution of soil profiles of different brackish irrigation treatment had obvious stratification phenomenon,the surface（0～10 cm）soil water content was high,and the average soil water content difference between each brackish irrigation treatment was not significant（P>0.05）,higher than CK+treatment.After two continuous seasons of saline water irrigation,soil salt accumulated gradually,which were indicated by the electrical conductivity of saturated extract（EC_e）of soil at 0～20 cm depth at the end of the second season was significantly higher than that in the first season.The EC_eof CK+was significantly lower than those of other treatments（P<0.05）.Salt accumulation was more evident in the surface soil layer.At the end of the growth season,the content of soil salt ions(Na⁺,K⁺,Ca²⁺,Mg²⁺,and Cl^-)increased significantly,mostly accumulated on the surface layer and were consistent with the salt distribution.Soil SAR showed the highest CK-treatment and decreased with soil depth,the change pattern of soil CROSS values was consistent with SAR,but slightly higher than SAR.Compared with CK+,saline water irrigation significantly reduced the photosynthetic properties,including net photosynthetic rate,transpiration rate,and stomatal conductance of lettuce（P<0.05）,thus resulting in the reduced yield,where the CK-gave the lowest biomass.The photosynthetic properties of T2,T5 and T8 treatments were significantly lower than that of CK,but higher than those of single salt ion stresses,indicating that T2,T5 and T8 treatments alleviated the harm of single salt ions to the growth of lettuce,and increased yield but without significantly difference（P>0.05）.After two-season saline water irrigation significantly increased the accumulation of K⁺and Cl^-in lettuce leaves（P<0.05）,but did not significantly affect the plant absorption of Ca²⁺and Mg²⁺.The correlation between ion content and photosynthetic properties in lettuce leaves under saline water irrigation showed a significant negative correlation between Na⁺content and biomass,indicating that Na⁺should cause the toxic effect on lettuce growth.These results could provide some theoretical basis and technical support for the risk assessment of long-term saline water irrigation with different water quality.