Increasing Cultivar Diversity of Processing Tomato under Large Scale Organic Production in California

Summary in the original language of the document

At an organic farm in California, higher plant diversity was hypothesized to enhance ecosystem functions and services. Plant diversity was manipulated temporally and spatially: mustard cover crop vs. no cover crop (fallow) in winter, and mixtures with one (farmer’s best choice), three, or five processing tomato cultivars in summer. Soil N, soil microbial biomass, crop nutrient uptake, canopy light interception, disease, GHG emissions and biomass were measured. Results show that the mustard cover crop reduced soil nitrate (NO3-) in winter and also during the tomato crop, which was associated with decreased growth and canopy development. All cultivar mixtures had fairly similar yield and shoot biomass. The ‘choice cultivar’ (i.e. farmer’s best choice) showed plasticity depending on the mixture, tending to have higher biomass production in mixtures. This study shows the complexity of cultivar-mixture interactions. To achieve the greatest benefit for ecosystem functions in organic farming, mixtures require greater understanding of cultivar plasticity and phenological and physiological trait diversity.