Transition from conventional to low-input agriculture changes soil fertility and biology

Growers converting from conventional to low-input and organic farming systems must rely on organic sources for adequate soil fertility. At the Sustainable Agriculture Farming Systems (SAFS) project at UC Davis, we measured soil fertility and biological parameters in four farming systems. By the end of the first 4 years, pH and percent nitrogen were consistently higher in organic and low-input than conventional plots for all crops. Levels of organic matter, phosphorus and potassium were significantly higher in the organic than conventional 2-year plots. Microbial biomass levels were consistently higher in organic and low-input systems, while plant parasitic nematode numbers were consistently lower. Nitrogen deficiency appeared to be a problem in organic tomatoes during the transition period. More research is needed into the dynamics of soil nutrient availability in low-input systems. For instance, we may need to develop new methods of assessing soil fertility in organically fertilized systems.