Research On The Improvement Effect And Mechanism Of Several Amendments On Coastal Saline Soil

The study of effective improvement measures is of great practical significance for the management and utilization of saline soils in North Jiangsu.The application of soil modifier is one of the main techniques of saline soil improvement,with considerable research results.Nitrogen is critical for crop growth and development,and its efficient utilization is an important way to realize sustainable development of agriculture.The aim of this study was to obtain suitable measures to improve the saline soil in northern Jiangsu coastal farmland.The combinations of difference soil modifiers and nitrogen application rates were investigated in coastal saline farmland with a local conventional wheat-rice rotation model.Soil physical and chemical properties,nutrient indexes,crop yield indexes and nitrogen apparent balance were determined.The effects of different soil modifiers on nitrogen transformation in coastal saline soil under culture conditions were studied.The main results are as follows(1)Effects of different regulating measures on the improvement of soilsSoil physical and chemical properties were not affected by nitrogen application rate.Under the condition of equal nitrogen,the effects of different modifiers varied.The treatment of biochar and straw furrow burial could effectively inhibit the surface aggregation of soil salt,but had little effect on the surface soil pH.Humic acid treatment had no obvious desalination effect,but could effectively reduce the surface soil pH.Desulfurization gypsum treatment could significantly reduce pH but increase the salt content of surface soil.The four modifiers used effectively reduced soil bulk density and improved soil water holding capacity,of which biochar treatment was the best,followed by straw ditch burial treatment.All modifiers could promote the formation of soil large aggregates.Soil organic carbon content was improved by soil modifiers,with the best results detected in the treatments of biochar and straw,followed by humic acid.(2)Effects of different regulatory measures on soil nitrogen and crop growthThere was a significant positive correlation between the amount of inorganic nitrogen in soil surface and the amount of nitrogen applied.The application of 225kg/ha nitrogen was beneficial to the accumulation of alkaline hydrolyzed nitrogen.Desulfurization gypsum could release urea slowly,while biochar and straw could promote the accumulation of inorganic nitrogen and alkali-hydrolyzed nitrogen.Compared with CK,each treatment had positive effect on yield increasing,but not on harvest index.The yields of wheat and rice were positively correlated with the amount of nitrogen applied without soil modifier amendment.The yields increased first and then decreased with the increase of nitrogen application accompanied with desulphurization gypsum,biochar or humic acid.With straw treatment,the yield of wheat was positively correlated with the amount of nitrogen applied,while the yield of rice increased and then decreased with the increase of nitrogen application rate.Under the condition of 150kg/ha and 225kg/ha nitrogen application,biochar amendment increase yield and nitrogen absorption the most,followed by desulphurization gypsum treatment and humic acid treatment,while straw ditch treatment reduced wheat yield.The yield-increasing effect of rice was second only to that of biochar treatment.Under the condition of 300kg/ha nitrogen application,the yield of wheat season was increased only by straw ditch embedding treatment,and rice yield in all the treatments were reduced.Overall,the application 225kg/ha nitrogen and biochar treatment achieved the best resutls.(3)Effects of different Control measures on apparent nitrogen balance and nitrogen use efficiencyThere was a significant positive correlation between apparent nitrogen loss and nitrogen application rate.Under the condition of equal nitrogen,the nitrogen loss of biochar treatment was the lowest.The apparent nitrogen loss accounted for a high proportion of nitrogen output.Only in the treatment of biochar with 225kg/ha nitrogen the nitrogen uptake was higher than nitrogen loss.High nitrogen recovery rates were observed under the condition of 150kg/ha and 225kg/ha nitrogen application,with the highest recovery rate in biochar treatment with 225kg/ha nitrogen rate.The agronomic efficiencies of nitrogen fertilizer in all treatments except biochar were negatively correlated with the amount of nitrogen application,and the recovery rate of biochar treatment was the highest.There was a negative correlation between nitrogen partial productivity and nitrogen application rate.Under the condition of 225kg/ha nitrogen application,and biochar treatment had the highest nitrogen partial productivity.Under culture conditions,ammonia volatilization loss increased first and then decreased with time.Soil salt promotes ammonia volatilization,and desulfurization gypsum could release urea slowly,reducing ammonia volatilization loss and inhibiting nitrification.The application of biochar had little effect on ammonia volatilization,while the inhibition effect on nitrification is second only to desulfurization gypsum.The application of fulvic acid promoted ammonia volatilization first and then inhibited it.