Assessment of Quality of Soils Under Organic Farming in South China

Little information is available as reference for assessment of effect of organic farming on soil quality with soils under conventional farming as control, although large volumes of reports demonstrate that organic farming can ameliorate degraded soils. Soil samples were collected from 14 farms (i. e. 7 organic farms and 7 neighbouring conventional farms) for analysis of soil physicochemical properties, i. e. bulk density, pH, organic matter, total N, total P, readily available P and readily available K, and biological properties as well, i. e. microbial biomass carbon, diversity and dominance of microbial communities, and population, diversity and dominance of nematodes. Statistics of the 13 indices was done for principal components analysis. Out of the 13, 6 (TN, pH, bulk density, microbial biomass carbon, and population and dominance of nematodes) were cited to form a minimum data set (MDS). Soil quality index (I_s,q,6) based on MDS was in the range of 0.39-0.72 in the soils under organic farming and in the range of 0.18-0.54 in the soils under conventional farming. The soils under organic farming, except in one sampling site were all higher than those under conventional farming in I_s,q,6. Based on the fact that the 6 indices in MDS, particularly dominancy of the nematode community, contributed 12.4%-21.8% to soil quality and that I_s,q,13(SQI derived from the 13 soil property indices) is significantly related to I_s,q,6(r=0.89, P<0.05), it is quite clear that MDS-based soil quality assessment is a workable and effective tool.