Response Of Red Soil Fertility Quality To Land Use Change

Soils in subtropical China have great potential for agricultural production.Recently,the change of land use in this area has a strong impact on soil physical and chemical properties and microbial communities,and then on soil fertility quality.In this study,different land use patterns(natural forests,artificial forests,chestnut orchards,sloping farmland and paddy fields),with clear land use history in hilly areas of eastern and Western Hunan,were selected as the research objects.Soil samples of 1 m deep soil profile were collected by self-made soil drill at 20 cm depth,and the changes of land use on granite were studied by routine physical and chemical analysis techniques.The effects of land use change on microorganisms and their communities in granite and slate red soils were studied by fatty acid mapping and high-throughput sequencing.The purpose of this study is to understand the dynamic evolution of soil fertility and quality after regional land use change,provide basic data and scientific basis for rational utilization of red soil resources,scientifically estimate the land use patterns in subtropical hilly areas.The main results were as follows:(1)The change of land use pattern has no significant effect on soil texture,but leads to the transformation of large water-stable aggregates to small water-stable aggregates.The bottom soil pH showed an overall upward trend,with the brook soil pH increased the most(0.2 to 2.3)than the Daweishan(0.3 to 1.3).The contents of organic matter and nitrogen showed a downward trend,ranging from 6% to 76% and from 6% to 69%.The total effective phosphorus content increased by 0.3 to 52 times.Compared with soil total nutrients(SI ranging from-0.8 to 19.9),available nutrient content(SI ranging from-0.8 to 51.8)is more sensitive to land use change,even in the opposite direction.Compared with topsoil,the available nutrient content of red soil is more sensitive to land use change.We can’t simply extrapolate the research conclusions of nutrients in shallow topsoil of different land use patterns to deep subsoil.We should pay attention to the evolution trend of nutrients in subsoil caused by land use change.(2)After the transformation of natural forests into other land use methods,the urease activity of the subsoil decreased by 16% to 98%,and the invertase activity of the red soil of granite showed an overall increase(in the range of 5% to 531%);In contrast,the invertase activity of the plate and shale red soil decreased by 14% to 97% overall.The microbial gene sequencing of plate and shale red soil showed that the conversion of natural forest to sloping land and paddy field increased the richness and diversity of soil bacterial community.However,after the change of Chinese fir plantation,the richness and diversity of soil bacterial community were Reduced.After land use change,the absolute content of soil PLFA increased,and the proportion of bacteria in the total number of three major microorganisms ranged from 72% to 87%,followed by fungi,actinomycetes and protozoa.After the transformation of natural forest,the microbial community species and microbial species of granite red soil increased,and the diversity of the most common species decreased in soil microbial community in 20-40 cm soil layer,but the degree and diversity of microbial species increased.The soil microbial community in the surface soil of shale and shale decreased,but the uniformity of microbial species distribution increased.The soil microbial community diversity decreased in 20-40 cm soil.(3)Through comprehensive analysis of 35 indexes of physical(8 items),chemical(14 items)and biological(13 items)properties of 0-20 cm topsoil,constructing a minimum data set by principal component analysis,to evaluate the soil fertility quality and calculate the comprehensive soil fertility quality index.The results showed that the minimum data set,for soil fertility quality evaluation of different land use patterns in eastern Hunan,included powder,clay content,aggregates of 0.25 to 0.053 mm,bulk density,total phosphorus,available phosphorus,exchangeable calcium and magnesium,available copper,invertase activity,bacteria,fungi,Gram-positive bacteria and total PLFA.The minimum data set,for soil fertility quality evaluation of different land use patterns in western Hunan,includes sand grains,bulk density,pH,available iron,available copper,total nitrogen,total potassium,exchangeable calcium,magnesium,urease activity,bacteria,fungi,actinomycetes,gram-positive bacteria,gram-negative bacteria,arbuscular fungi,protozoa and total PLFA.After land use change,soil fertility quality showed a downward trend as a whole.After the change of land use pattern,the comprehensive soil fertility quality index can better reflect the characteristics of soil fertility quality than a single factor.