Near-critical Water Liquefaction Of Biomass And Its Products For Saline Soil Improvement

In arid and semi-arid regions,soil salinization greatly threatens agricultural production,food security and sustainable development.According to incomplete statistics from United Nations Educational,Scientific and Cultural Organization(UNESCO)and Food and Agriculture Organization of the United Nations(FAO),the global saline land area is 954 million hectares.China has the third largest saline land area in the world,with about 99.13 million hectares(about 1.5 billion mu).Due to many factors such as urbanisation and soil degradation,the available arable land area has been reduced.One of the goals pursued by the international community is to develop sufficient arable land to meet human demands for food.Improving saline land can significantly increase the supply of arable land.The use of renewable biomass as raw materials for saline land improvement is more significant in terms of green cycle.In this study,biomass liquefaction experiments were conducted by near-critical water technology with biomass maize straw and chicken manure as raw materials.Biomass liquefaction experiments were carried out by near-critical water technology with biomass maize straw and chicken manure as feedstock.The solid product(SMLP-S)and the liquid product(SMLP-L)were analysed to obtain the optimum liquefaction process.Based on the characteristics of the products,the liquefied products were applied to saline soils.The effects of liquefied products on soil p H,electrical conductivity(EC),organic matter and crop yield were analyzed.The soil improvement programs were optimized according to the improved products.Field improvement and planting experiments were carried out to research the effect.The main contents are as follows:1.SMLP-S was prepared by liquefied corn straw and chicken manure using near-critical water technology.SMLP-S had high yield,high specific surface area and high nutrient content.This study investigated the effect of the mixing ratio of maize straw and chicken manure on the structure and properties of SMLP-S50.The SMLP-S50 was prepared at a liquefaction temperature of 220℃and a mass ratio of straw to chicken manure of 1:1.The results showed that the SMLP-S50 yield was 62.67%,the p H was4.79,the organic matter content was 59.81%,and the total nitrogen,phosphorus and potassium were 1.34%,1.18%and 1.05%respectively.SMLP-S50 had a specific surface area of 80.42 m~2/g and an average pore size of 12.70 nm.2.Using SMLP-S50 carried out laboratory saline soil improvement experiments.The soil was treated with SMLP-S50 of 0 t/ha,0.025 t/ha,0.05 t/ha,0.75 t/ha and 0.10t/ha respectively.The results showed that when SMLP-S50 was treated at 0.05 t/ha,the saline soil p H decreased from 8.42 to 7.94 and EC decreased from 0.453 ds/m to 0.306ds/m.Soil organic matter and nutrients such as total nitrogen,effective phosphorus and fast-acting potassium increased significantly,and the combined treatment was optimal.3.SMLP-S50 of 0.05 t/ha was used to carry out field improvement test of saline-alkali soil.Corn was selected as a planting crop.After a natural growth cycle,the physicochemical properties of saline soil and the growth status of maize were analyzed.The results showed that the p H of the improved plot decreased from 8.56 to 7.88,the EC decreased from 0.43 ds/m to 0.19 ds/m,the water content increased from 1.35%to1.96%,and the soil organic matter content increased from 6.73 g/kg to 10.44 g/kg.The physical and chemical properties of saline-alkali soil were significantly improved.The results of the expert group showed that the yield of corn mu in the improved plot increased by 46.3 kg(1389 kg/ha)compared with the control plot,and the yield increased by 12.00%.4.SMLP-L was prepared by high temperature liquefaction of maize straw and chicken manure in near-critical water.SMLP-L was rich in bioacids and nitrogen heterocyclic compounds.The optimum process conditions were optimised by analysing the effect of liquefaction temperature on the composition of the liquid product.SMLP-L220 was prepared at a liquefaction temperature of 220°C and a mass ratio of straw to chicken manure of 1:1.SMLP-L220 had a p H of 4.45 and a density of 0.9946 g/m L.SMLP-L220 contained a large number of organic compounds,mainly acids(40.54%),alcohols(20.84%),pyrazines(15.77%),phenols(9.03%),esters(2.58%),ketones(9.07%)and other organic compounds(2.18%).Using SMLP-L220 carried out saline soil amendment trials.Barley was used as the test crop.The results showed that after treatment with a 50-fold dilution of SMLP-L220,soil p H and EC decreased,with soil p H falling from 8.39 to 7.34 and EC decreasing from 0.491 ds/m to 0.457 ds/m.Compared to the control check,the nutrient content increased and barley germination,root length and spike length increased by 27.27%,31.29%and 8.45% respectively.