Effects Of Different Amelioration Techniques On Soil Saline-alkali Characteristics In Songnen Plain

Songnen plain is not only an important grain production base in China,but also one of the major distribution areas of saline-alkali soil in the world.Soil salinization and alkalization in this region is a serious threat to food security of China.Therefore,soil improvement as an important measure to reduce soil salinization and restore agricultural production has been widely concerned.Scientific understanding of soil salinization characteristics of Songnen plain,studying the effects of different methods on saline-alkali soil improvement and proposing reasonable technical measures,which is of great significance to promote the mitigation of soil salinization and alkalization and the rational development and utilization of land resources in the region.In this study,the characteristics of soil salinization of Songnen alkaline grassland were scientifically understood through field investigation.Then,the field test was carried out to verify the improvement effect of water spraying and sand mulching on saline-alkali land.Secondly,leaching tests were carried out in laboratory to clarify the effects of sandy soil and straw addition on soil desalinization efficiency.Finally,the influence of different land use types on saline-alkali soil properties were investigated based on a long-term field experiment platform in alkaline grasslands.The main results are as follows:（1）There were significant differences in salinity characteristics of soil among different communities,including bare land,Puccinellia tenuiflora,Leymus chinensis,Chloris virgata and Suaeda glauca communities,especially in the surface soil（0-10cm）.The soil pH of Leymus chinensis communities in the surface soil was 9.76,which was 4.2%～7.0%lower than that in other community types.The soil electrical conductivity of Leymus chinensis communities in the surface soil was 279μS/cm,which was 68.1%～87.3%lower than that in other vegetation communities.In addition,the contents of soil Na⁺,HCO₃^-and total alkalinity in the surface soil also showed similar changes with soil pH and electrical conductivity across community types,the Na⁺content was 0.343 g kg^-1,the HCO₃^-content was 0.773 g kg^-1,the total alkalinity was 2.53 mmol_c L^-1,which were 70.2%～81.0%,65.6%～76.0%and 67.4%～76.9%lower than those in other vegetation communities,respectively.Compared with bare land,plant growth changed the distribution of soil electrical conductivity in 0-100 cm soil layer.The soil electrical conductivity of bare land decreased with the increase of soil depth.However,the soil electrical conductivity of vegetation communities showed">"type distribution along the soil profile.In this study,the main soil dissolve salt ions are Na⁺and HCO₃^-in all vegetation communities,which have significant positive correlations with soil pH and electrical conductivity.（2）Water spraying significantly decreased the soil pH,electrical conductivity,total salt and soil dissolve salt ions concentrations in 0-20 cm soil layer,but the soil pH,electrical conductivity and total salt concentrations in 20-50 cm soil layer showed increasing trends.Compared with water spraying,the combination treatment with water spraying and 10 cm sand mulching decreased soil pH,electrical conductivity and Na⁺content by 6.2%,67.1%and 37.3%,respectively.When the sand mulching thickness increased from 10 cm to 15 cm,the soil pH,total salt and HCO₃^-concentrations in 0-30 cm soil layer significantly decreased,the plant number of Avena sativa,Medicago sativa and Sorghum sudanense were 15,115 and 33 individuals·m^-2 respectively,which were 150%,167%and 313%higher than those in 10 cm sand mulching,the plant height were 56 cm,37 cm and 165 cm respectively,which were 30.4%,19.5%and 23.8%higher than those in 10 cm sand mulching,the plant aboveground biomass were 87 g,62 g and 270 g·m^-2respectively,which were 191%,69.5%and 32.2%higher than those in 10 cm sand mulching.Under the water spraying treatment,the soil electrical conductivity,total salt and dissolve salt ions contents,SAR and total alkalinity in 0-20cm soil layer had no significant decreasing trend when the sand mulching thickness increased from 15 cm to 20 cm,and there were no significant differences among the plant number,plant height and plant aboveground biomass of Avena sativa,Medicago sativa and Sorghum sudanense.（3）In this study,adding 0.2%,0.4%,0.6%and 0.8%straw to saline-alkali soil could significantly improve soil desalination efficiency.The pH and electrical conductivity of soil leaching solution increased significantly when the straw was added into soil.After leaching,the soil electrical conductivity for adding straw treatments were 134～487μS/cm in 0～25 cm,which were 54.4%～84.7%lower than that in control,the total alkalinity were 0.73～16.82 mmol_c L^-1,which were 16.2%～93.6%lower than that in control,the Na⁺concentrations were 0.055～1.009 g kg^-1,which were12.0%～94.6%lower than that in control,and the HCO₃^-concentrations were0.220～4.745 g kg^-1,which were 14.3%～93.0%lower than that in control,respectively.With the increase of addition amount of straw,the soil desalination efficiency showed an increasing trend.Compared with adding 0.2%straw treatment,the electrical conductivity of soil leaching solution increased by 26.3%～65.8%under 0.8%straw addition treatment.After leaching,the soil electrical conductivity,Na⁺and HCO₃^-concentrations in 0-25 cm soil layer decreased by 26.0%～42.3%,20.2%～91.2%and58.0%～91.9%,respectively.Adding sand into saline-alkali soil could improve soil desalination efficiency.Compared with the control,the pH of soil leaching solution significantly increased when 40%and 60%sand was added into soil.After leaching,the soil pH,electrical conductivity,dissolve salt ions concentrations and total alkalinity decreased significantly in 0-25 cm soil layer.Under 40%,60%and 80%sand treatments,the pH and electrical conductivity of soil leaching solution decreased with the increased addition amount of sand,and the soil pH,electrical conductivity and total alkalinity in0-25 cm also showed decreasing trends.（4）At temporal scale,the change trends of soil water content in 0-50 cm soil layer were similar across Leymus chinensis grassland,alfalfa grassland,corn grassland and restored grassland,and the soil electrical conductivity was smaller in 0-10 cm soil layer,ranging from 162～179μS/cm.There were no significant differences in the mean electrical conductivity and total salt content in 0-10 cm soil layer among four land use types.The mean pH and electrical conductivity in Leymus chinensis grassland were9.80～9.95 and 397～553μS/cm in 10-50 cm respectively,which were 1.6%～8.3%and19.2%～130.9%higher than those in other land use types.The soil Na⁺and HCO₃^-concentrations accounted for 50%～70%of dissolve cations and anions contents under different land use types.There were no significant differences in soil dissolve cations and anions concentrations,CO₃^2-and HCO₃^-concentrations,total alkalinity in 0-10 cm soil layer among different land use types.However,the soil Na⁺concentrations and SAR in alfalfa grassland were significantly larger than those in other land use types.