Characteristics Of Soil Qualities Evolution Under Different Land Use Patterns In A Coastal Saline Soil

The reclamation of coastal soils is to solve more people and less land, lack of land resources in coastal areas. Reclamation date and land use are the direct influence factors of soil fertility. The aim of our research was to investigate how a reclaimed coastal soil chronosequence and land uses affected soil fertility, biomass, activity and community structure of soil microorganisms and provide a theoretical basis for the establishment of a soil fertility characteristic index system in a coastal saline soil in Shangyu, Zhejiang Province, China.An experiment was carried out with different land use patterns(vegetables, cotton and rice) along a reclaimed coastal soil chronosequence(1950、1974、1976、1994 and 1996) by using quantitative PCR and phospholipid fatty acid(PLFA) profiling analysis in the east coastal region of China. The results showed the following conclusions:1) Soil organic matter, available phosphorus and available potassium contents in the 0-40 cm soil layer decreased with increasing reclamation time in the paddy fields. Soil organic matter, total nitrogen,and alkali solution nitrogen contents in 0-20 cm soil layer were the higest in the cotton fields in 1990 s,but those in 20-40 cm soil layer the higest in the paddy fields, soil organic matter and total nitrogen contents in 0-20 cm soil layer were the higest in the paddy fields in 1970 s. Soil organic matter content decreased in 1970 s, but the content of available potassium increased with the increase of soil depth.2) Soil sulfatase activities in the 0-20 cm soil layer increased, in the paddy and cotton fields with increasing duration of reclamation, soil phosphatase and beta glucosidase activities in 40-60 cm soil layer reached the highest in the paddy fields reclaimed in 1976, 113.1 μg/g·h, 45.25 μg/g·h,respectively. Soil phosphatase activities in 0-40 cm soil layer followed a decreasing order as paddy field > vegetable field > cotton field reclaimed in 1990 s, and soil phosphatase activities in were in the0-60 cm soil layer followed a decreasing order of paddy field > cotton field> vegetable field reclaimed in 1970 s. With the increase of soil depth soil enzyme activity decreased gradually.3) Soil microbial biomass, bacteria, fungi and Gram-positive bacteria and Gram-negative bacteria(PLFAs) in the 0-20 cm soil layer gradually increased in the paddy fields with the increase of reclamation time. Total microbial biomass(PLFAs) of the 0-20 cm soil layer was the highest in the paddy fields reclaimed in 1976, and reached 2.77 nmol/g. Soil bacteria PLFAs in the 0-20 cm soil layer were in the order of vegetable field> cotton field> paddy field reclaimed in 1990 s and followed as the order of paddy field > cotton field> vegetable field reclaimed in 1970 s. With the increase of soil depth soil microbial biomass decreased gradually.4) The relative expression of soil AOA and NOSZ genes in 0-20 cm soil layer decreased in the cotton and paddy fields with increasing duration of reclamation. The expression levels of soil AOA,AOB, NIFH and 18 S genes were the highest in the paddy fields reclaimed in 1976. Among the three land use patterns, soil AOA and NOSZ genes in 20-40 cm soil layer were higher, in the paddy fields and soil AOA, NOSZ and 18 S genes in 40-60 cm soil layer were the highest in the cotton fields. All the soil genes in the vegetable fields did not change significantly with soil depth.5) The correlation analysis showed that soil dehydrogenase activity and soil available potassium content were significantly positive correlation, the correlation coefficient reached 98%. There was a good positive correlation between soil bacteria and soil organic matter, total nitrogen, available phosphorus and available phosphorus. The correlation between soil microbial and soil available potassium was not significant.