2.1. Soil sampling site
The location of soils is at Sunjia agricultural catchment, 4 km
northwest of Ecological Experimental Station of Red Soils in Yingtan,
Jiangxi province, China. The soils in the catchment originated mainly
from Quaternary red clay, and are characterized by loam and clay
loam texture (Table 1). The soils from upland are classified as Ultisols
based on the USDA Soil Taxonomy (Soil Survey Staff, 2010). Ultisols
located in the valley have been cultivated for paddy rice for different
years. Soil properties in paddy fields changed much from Ultisols after
long-term cultivation under redox conditions so that they are classified
as Anthrosols in international soil classification system (IUSS Working
GroupWRB, 2014).