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  • Author or Editor: Jeff Mitchell x
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A 2-year field study was conducted within the Sustainable Agriculture Farming Systems Project at the Univ. of California, Davis, to evaluate the effects of long-term conventional (CONV), low-input (LOW), and organic (ORG) production practices on processing tomato fruit mineral composition and quality. To establish relationships between soil chemical properties, soil water content, fruit mineral composition, and quality, this study characterized soil chemical properties and monitored soil water content through each tomato season. Soil total C, N, soluble P, exchangeable Ca, K,and Na were higher in the organic system than in the conventional system. Higher soil electrical conductivity was found in the CONV system compared to the other systems. Low input plots had soil characteristics intermediate to the other farming systems. Marketable and unmarketable yields were similar among the farming systems. Fruit N and Na were lower in the organic and low-input systems than in the conventional system. Fruit P and Ca contents were higher in the organic system than in the conventional system as a result of 11 years of manure applications. Soluble solids content, titrable acidity, color, and soluble solids yield were lower in 1998 in the organic system than in the conventional system, while no differences were found in 1999. Soil water content during the ripening stage was the major factor affecting the soluble solids content of the organic system. In the low input and conventional systems soluble solids content was most related to soil exchangeable Ca and EC, respectively.

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Three systems for fresh-market tomato production (transplanting into reflective mulch, transplanting into a cover crop that had been chopped and killed, and standard transplanting into fallow beds) were evaluated in two field experiments in California's San Joaquin Valley in 1999. The first study was a spring tomato planting (April) and summer (July) harvest in which a mixture of rye, triticale, and vetch was used as the cover crop mulch. The second trial consisted of a summer tomato planting (July) and fall (September) harvst in which a sorghum/sudan hybrid was used as the mulch. In both experiments, tomato plants growing over the reflective mulches accumulated significantly more biomass than did plants growing in the other production systems. These larger, more-robust plants growing over reflective mulch also produced significantly higher yield. In the summer planting, there was almost no tomato biomass accumulation in the cover crop plots due to the fact that the sorghum-sudan hybrid we chose as the cover crop turned out to be allelopathic to tomatoes when shredded and used as a mulch.

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Soil incorporation of biochar appears to increase plant growth in some environments. However, the effect of biochar on root system architecture (RSA) or on weeds is not well understood. Our objective was to examine the effect of biochar on the growth and RSA of large crabgrass (Digitaria sanguinalis L. Scop.), a common and problematic weed. Plants were grown in rhizoboxes filled with field soil ± either a low-nutrient biochar (LNB) or a high-nutrient biochar (HNB). Rhizoboxes were either filled uniformly with field soil ± biochar (solid) or with + biochar and − biochar-amended field soil so that each occupied half of the rhizobox (split). Large crabgrass biomass and RSA were affected by biochar type in the solid design rhizoboxes and large crabgrass roots proliferated in biochar-amended soil in the split rhizoboxes, regardless of biochar type. This study provides evidence that plant roots can detect and grow toward biochar and suggests that the addition of biochar to soils may increase the ability of large crabgrass to spread vegetatively.

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This article summarizes the current status of organic vegetable production practices in California. The production of vegetables organically is growing rapidly in California, led in large part by growth in the market demand for organically grown produce. Key aspects of organic vegetable production operations such as certification and farm production planning, soil management, weed management, insect management, and plant disease management involve special practices. Many practices have not been thoroughly researched and the scientific base for some practices is still being developed.

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