Mechanism Study On Improvement Of Red Soil By Hydrothermal Carbonization Of Pig Manure

The annual amount of livestock and poultry manure discharge is up to billions of tons,along with continuous increase trend.Note that pig manure discharge accounts for more than 70%.At present,the neutralization rate of livestock and poultry manure is less than 70%.Livestock manure contains underutilized antibiotics,heavy metals and organic matter,etc.,which will bring huge environmental issue without properly disposing.The hydrothermal carbonization of livestock and poultry manure does not need to be dried in advance,and it is quickly converted the pig manure into hydrochar for returning to the field.It can not only reduce harmless livestock and poultry manure to the greatest extent,but also convert organic matter,nutrient elements and mineral elements in livestock and poultry manure into resources.Hydrothermal carbonization also helps mitigate climate warming by sequestering carbon.In view of the fact that the influence mechanism of hydrothermal charcoal converted from livestock and poultry manure on soil physicochemical properties and plant growth was insufficient,this paper prepared hydrochar from pig manure at different temperatures(160℃,180℃,200℃,220℃)under the conditions of selected reaction time and solid-liquid ratio.The improvement of red soil by hydrochar was investigated through sprouting test of Chinese cabbage(hydrochar added ratio 0.1%,0.5%,1%,1.5%,2%)and pot experiment(hydrochar added ratio1%).The main research results are as follows:(1)With the increase of reaction temperature,the physical and chemical properties,nutrient elements,heavy metal content,morphology and structure of hydrothermal carbon change greatly,especially at 220℃:the hydrochar yield of pig manure decreased from 93.48% to 69.77%;p H decreased from 7.15 to 6.69;Ash content increased from 27.39% to 33.36%.EC increased from 3.24 ms/cm to 3.37ms/cm;Organic matter content decreased from 70.47% to 64.68%.The total nutrient(N+P+K)content was more than 85g/kg.The bioavailability of Cu,Zn and Mn presented a decreasing trend,but the total metal content of Cu,Zn and Mn decreased first and then increased,and the total heavy metal content of hydrochar prepared at180℃ was the lowest.The surface of hydrochar contains a large number of oxygen-containing functional groups.The specific surface area and total pore volume decreased with the increase of temperature in the temperature range of160℃～200℃,and the pore size increased with the increase of temperature.The maximum specific surface area and pore structure was found at 220℃.The results showed that hydrochar prepared at low temperature had more potential for soil improvement.(2)The hydrotchar from pig manure prepared at low temperature(160℃ and180 ℃)could promote the germination of Chinese cabbage seeds,while the hydrochar from pig manure prepared at high temperature(200 ℃ and 220℃)showed phytotoxicity.The optimum application concentration of pig manure hydrothermal charcoal prepared at each temperature was different,but according to the growth of plants after seed germination,it was considered reasonable to apply1% concentration in subsequent pot experiments(germination rate was more than70%).(3)Hydrochar can generally improve the red soil "acid,thin,sticky,plate" problem.At 1%,hydrochar prepared at different temperatures had positive effects on physical and chemical properties of red soil,such as bulk density,field capacity,porosity,p H,EC,CEC,etc.,compared with red soil control group.Meanwhile,the application of pig manure and hydrochar could increase the organic matter content of red soil by 10.18g/kg,7.80 g/kg,9.04 g/kg,3.35 g/kg and 3.45g/kg,respectively.Total N,P,K and available nutrients were higher than those in red soil control group(except that there was no significant difference between total K and red soil in experimental group).According to the plant feedback effect,the application of hydrothermal carbon in red soil can promote the growth and development of Chinese cabbage,improve the above ground and underground fresh weight,above ground and underground dry weight,leaf area and plant height agronomic traits.At 1%,hydrochar at 200℃ has the best effect on plant growth.In conclusion,the organic matter and nutrients of pig manure are more than twice of the minimum standards(organic matter content ≥30%,total nutrient(N+P+K)≥40g/kg)in Organic Fertilizer(NY/T 525-202021),and contain a large number of oxygen-containing functional groups.Although the morphology and structure of pig manure vary,pot experiment shows that,The hydrothermal carbon of pig manure at different temperatures can improve the red soil.