Application Of Biochar Combined With Nitrogen Fertilizer In Water And Salt Regulation And Nitrogen Utilization Of Ipomoea Aquatica

According to data from the Third National Land Survey,by the end of 2019,cultivated land in China have reduced by more than 10 million acres annually,approaching the red line of 1.8 billion acres of cultivated land protection.As an important back-up land resource,saline soils have great potential for exploitation.However,saline soils generally suffer from high salt content,low hydraulic conductivity and low nitrogen use efficiency,which seriously restrict regional economic growth and sustainable ecological development.In recent years,biochar has been widely used to amend soils and increase nitrogen use efficiency.Therefore,saline soils in the beach area of northern Jiangsu Province were used as the object of study,through indoor soil column simulation experiment and potting experiment,investigate the effects of biochar with nitrogen fertilizer on soil water and salt transport,physical and chemical properties of soil,growth and nitrogen use efficiency of ipomoea aquatica.Six treatments were set up for indoor soil column simulation tests,B0N150,B0N250,B4N150,B4N250,B8N150,B8N250.Potting experiment were set up with nine treatments based on two factors:biochar application(0%,4%,8%)and nitrogen fertilizer application(0 mg/kg,150 mg/kg,200 mg/kg).The main research findings obtained are as follows.(1)The application of biochar promotes the infiltration of soil water and a moderate amount(4%)of biochar can inhibit evaporation of soil water.The maximum migration distance of wetting,cumulative infiltration and stable infiltration rate were achieved with the appropriate amount of biochar(4%),while the cumulative evaporation and daily evaporation intensity were minimized,with the best water retention and evaporation restrain effect.(2)The application of biochar increased the soil water content in the profile and enhanced the soil water holding capacity.The 4%biochar addition treatment promoted the salt leaching and effectively inhibited the return of salts to the surface soil,which had a good salt regulation effect,while the salt peak of the high application rate(8%)of biochar treatment shifted up more significantly.The addition of biochar slows down the leaching of nitrate nitrogen,promotes the conversion of soil nitrogen and has a holding effect on soil nitrogen.(3)The main effect of biochar on soil bulk density and porosity was significant.The addition of biochar increased soil porosity and decreased soil bulk density.Moreover,the addition of biochar effectively reduced soil salinity and increased soil nutrient content.The contents of total nitrogen,nitrate nitrogen,organic carbon and organic matter in soil increased with the increase of biochar addition.The contents of available potassium and available phosphorus in soil treated with biochar and nitrogen fertilizer were higher than those treated with biochar or nitrogen fertilizer alone.Analysis of variance shows that the main effects of biochar and nitrogen fertilizer and their interaction had significant effects on soil available potassium and available phosphorus.(4)Suitable application of biochar(4%)and nitrogen fertilizer(N150)could promote the growth of ipomoea aquatica.Suitable application of biochar(4%)and nitrogen fertilizer(N150)could improve the yield of ipomoea aquatica.The addition of 4%biochar could effectively improve the net photosynthetic rate,transpiration rate and chlorophyll content of ipomoea aquatica.Analysis of variance showed that the addition of biochar,nitrogen fertilizer and their interaction had significant effects on the content of soluble protein and soluble sugar of ipomoea aquatica,and the combination of biochar(4%)and nitrogen fertilizer(N150)promoted the content of soluble protein and soluble sugar of ipomoea aquatica.(5)The main effects of biochar and nitrogen fertilizer and their interaction had significant effects on nitrogen content,nitrogen accumulation,nitrogen partial factor productivity and nitrogen absorption efficiency of ipomoea aquatica.The nitrogen content,nitrogen partial factor productivity and nitrogen absorption efficiency of ipomoea aquatica were improved by combining application of biochar with nitrogen fertilizer.The nitrogen accumulation of ipomoea aquatica was improved by combining application of 4%biochar with N150 nitrogen fertilizer,and the nitrogen partial factor productivity and nitrogen absorption efficiency were improved best,the values were respectively 83.923kg/kg and 0.603kg/kg.In conclusion,the application of biochar combined with nitrogen fertilizer can improve the soil structure and water and salt environment,enhance soil fertility,promote the growth of ipomoea aquatica,and improve the nitrogen use efficiency to a certain extent.Based on the evaluation results of grey multidimensional comprehensive membership degree,B4N150 treatment,namely 4%biochar combined with 150 mg/kg nitrogen fertilizer,is a better improved fertilization scheme for saline soil under the condition of growing ipomoea aquatica.