Near-critical Water Liquefaction Of Corn Stalk And Its Solid Products For Saline Soil Improvement

China is a large agricultural country with abundant straw resources.The annual output of agricultural waste straw is about 1 billion tons.As an important biomass resource,it is conducive to sustainable agricultural development and improvement of ecological environment when straw resources are used in a rational and scientific way.Now,the situation of arable land resources is severe in China.Not only is there a shortage of arable land resources and serious pollution,but also problems such as soil degradation and salinization.Soil salinization has seriously hindered the development of agriculture and rural areas,and affected farmers'income,regional economic and ecological sustainable development.Straw is liquefied by near-critical water to make value-added utilization in this paper.It reduced the pollution of straw burning and provide a technical option for agricultural development and saline soil improvement.In this paper,corn stalk was liquefied by different conditions.Firstly,acidic solid product(ASP)was analyzed to obtain the optimal process.Secondly,ASP was used to conduct improvement potting experiments in saline soil.Finally,the field experiments based on laboratory data were carried out in Tongyu County,Baicheng City,Jilin Province(a national-level poverty-stricken county)to evaluate the effects of ASP on saline soil improvement and crop growth.The main contents are as follows:1.ASPs are prepared by liquefying corn stalks in near-critical water and analyze the properties.The corn stalk is liquefied at different solid-liquid ratios(the quality of corn stalks:the volume of water is 1:1,1:2.5,1:5,denoted as A,B,and C respectively)and different temperatures(190?,210?,230?,250?)to obtain ASP.The yield,pH,nitrogen,phosphorus,potassium,and organic matter content of ASP were measured.TG,FT-IR,SEM,BET,XRD are used for characterization to determine the optimal process at the same time.The optimal process is:the solid-liquid ratio of raw materials is 1:2.5,the liquefaction temperature is 230?,and the pressure is 4.7 MPa.The product is ASP-B230.2.ASP-B230 was used for the pot experiment of barley in saline soil.The soil was treated with ASP-B230 of 0,0.3,0.6,1,6,and 15 t ha^-1 respectively,and then plant barley.The results showed that the soil moisture content,soil available phosphorus content and soil organic matter content were increased after ASP-B230 treated the soil.And soil pH,electrical conductivity(EC),soil total nitrogen content and available potassium content were reduced.The dry weight of barley increased significantly when the ASP-B230 treatments were 0.6 t ha^-1,1 t ha^-1 and 6 t ha^-1.3.ASP-B230 was used for the field experiments of sorghum in saline soil.And the ASP-B230 were rotated into the soil surface with 0,0.15,0.3,0.45,0.6,0.75,1,6,and15 t ha^-1.Other management measures were the same as local agronomic measures.Comparing the physical and chemical properties of soil and crop growth conditions after a natural growth cycle.The results showed that the soil moisture content,nitrogen content,available phosphorus content,available potassium content,and organic matter content were increased.Soil salinity,pH,EC are reduced;K⁺,Ca²⁺,Mg²⁺content are increased,soil soluble Na⁺content is reduced;soil cation exchange capacity(CEC)is increased,soil exchange sodium percentage(ESP)is decreased.The ASP-B230 played a positive role in improving saline soil.In addition,it promotes the growth of sorghum roots and stems,and increases the 100-grain weight,spike weight and yield of sorghum after the soil were treated by ASP-B230.Considering comprehensively,the optimal treatment range is 0.6 t ha^-1?1 t ha^-1,and the 1 t ha^-1 treatment is the best.