Increasing Soil organic matter (SOM) content is important in improving soil fertility; however, conventional farming practices generally lead to a reduction in such organic material. Professor Jinshui, Wu, , Institute of Subtropical Agriculture, CAS and his group initiated a comparative study of organic and conventional arable farming systems in Shanghai, China to determine the influence of management practices on soil chemistry, microbial activity, and biomass since 2007. Soils obtained at 0–10 cm depth were analyzed using an approach combining traditional soil analysis, microbiological analysis using enzymology and microcalorimetric techniques, and a written survey of management practices among the farmers to understand how organic production systems improve soil quality and fertility.

Organic management resulted in significant increases (p<0.001) in total organic C and total N, Olsen-P, cation exchange capacity (CEC), soil respiration, microbial biomass C (Cmin) and N (Nmin), and alkaline phosphatase and urease activity. Sucrase activity was highest in conventional management in plastic tunnel fields (CNV-GR) soil and lowest in conventional management in open fields(ORG-OP) and conventional management in open fields(CNV-OP) soils. No significant difference was observed between ORG-OP and CNV-OP. The Olsen-P, TOC, total N, CEC, Nmin, sucrase and alkaline phosphatase activities were greater in greenhouse soils than those under open field cultivation, which indicated a higher level of soil management under greenhouse conditions.

The microcalorimetry power-time curves for all samples described typical microbial metabolic activity. In soil samples supplemented with glucose and ammonium sulfate the heat dissipation per cell unit suggested that microorganisms in soils under organic management had more efficient metabolism. In addition, microbial growth in soils under conventional management displayed lower growth rates, lower peak heat, and longer peak heat times, all of which indicated lower activity of soil microorganisms, compared with organic management. There was a large positive correlation (p<0.01) between the values of Pmax (the peak value of thermal power), Qtotal (total heat flux), and k (microbial growth rate constant) and the chemical properties. However, there was a significant negative correlation (p< 0.05) between the value of tmax (the time required to reach peak thermal power) and chemical properties other than sucrase activity.

Taken together, organic production systems significantly improved soil microbial characteristics and increased soil organic C, thus improving soil quality and fertility. Further studies investigating the long-term functional significance of carbon sequestration under organic practices are therefore warranted.

This research result was published on the recently issued Journal of Soils and Sediments (2010, DOI: 10.1007/s11368-010-0293-4).