Influence of agricultural land use changes on soil physiochemical and biological characteristics in Southern Jiangsu Province

Objectives The changes in soil physiochemical and biological properties, which might be induced by recent agricultural land use type change (ALUT) in Southern Jiangsu Province, were investigated. The results would provide valuable information concerning the soil fertility response to typical ALUT changes, and used for soil quality assessment and land use management.

Methods Soil samples from paddy field and peach orchard that was converted from paddy field for several years were collected in May (wheat-growing season) and July (rice-growing season) of 2017, respectively. Soil physical and chemical properties were measured using routine methods, enzyme activities using 96 microwell ELISA plate fluorescence analysis method, bacteria 16s rRNA gene abundance and fungal ITS gene abundance using quantitative real-time PCR.

Results Compared with paddy soil, the soil bulk densities were increased, the total pores volumes were not changed significantly, but the capillary pores were decreased and non-capillary increased significantly, indicating the soil became compacted. The soil pH showed a declining trend. The soil organic carbon content of the peach orchard declined compared with the paddy soil, whereas the total and available phosphorus contents were increased. The abundance of bacterial 16S rRNA genes was decreased, whereas that of fungal ITS rRNA was increased in orchard soils, compared to the paddy and wheat field soils, indicating soil organic carbon (SOC) degraders in orchard soil possibly transformed from "bacterial type" to "fungal type". Correspondingly, the enzyme activities related to nitrogen transformation and catalase in soil were reduced. From spring to summer, both of the peach orchard and paddy field soils experienced a reduction of organic carbon content, especially in the paddy field. Moreover, the abundance of16s rRNA and fungal ITS rRNA genes, and the activities of cellulase and invertase in soil were decreased significantly.

Conclusions The land use pattern change from paddy-wheat rotation to peach orchards in southern Jiangsu Province will significantly increase soil bulk density, decrease soil pH, increase soil P contents, decrease soil organic carbon contents, which ultimately lead to microbial ecosystem transfer from bacteria type to fungal one, and consequently impact soil nutrient cycling and carbon sequestration.