FUNDAMENTAL DIFFERENCES BETWEEN CONVENTIONAL AND ORGANIC TOMATO AGROECOSYSTEMS IN CALIFORNIA

In an integrated, multidisciplinary study we compared ecological characteristics and productivity of commercial farms categorized as either organic (ORG) or conventional (CNV) based on their use of synthetic fertilizers and pesticides or reliance on organic soil amendments and biological pest control. We measured belowground parameters: various soil chemical and biological properties and root disease severity; common agronomic indicators: biomass, fruit yield and insect pest damage; and community level indicators, including arthropod diversity and soil microbial activity and diversity. CNV and ORG production systems could not be distinguished based on agronomic criteria such as fruit yield and arthropod pest damage levels. However, differences were demonstrated in many soil, plant, disease, and diversity indicators suggesting that the ecological processes determining yields and pest levels in these two management systems are distinct. In particular, nitrogen mineralization potential and microbial and parasitoid abundance and diversity were higher in ORG farms. Differences between the agroecosystems were sufficiently robust to be distinguished from environmental variation and suggest that biological processes compensated for reductions in the use of synthetic fertilizers and pesticides.