Organic strip till plot at UCDavis Vegetable Crop Station (the pink flag is 76R MYC+(mycorrhizal plant) and green flag is rmc (non-mycorrhizal))

Evelyne Ndiaye, Louise Jackson

A mycorrhiza-defective (rmc) tomato mutant with very low or no AM colonization and its wild type progenitor (76R MYC+) with high colonization were used in a pot study and in a field research station to investigate the effect of zinc addition at different scales (patches or bands) on plant nutrient uptake. Zinc was added as a patch of ZnO and Zn68 (18 days after planting) in the microcosm study and as a band of ZnSO4 in the research station study. Zn uptake was monitored over time and concentration of macro and micro nutrients were also determined.

Preliminary results showed early (7 weeks after planting) Zn uptake by 76R MYC+ plants was greater than rmc plants in pot study but at harvest (9 weeks after planting) both genotypes had same Zn concentration. The early Zn uptake by mycorrhizal plant was not observed at the research station but shoot biomass was significantly higher for the non-mycorrhizal plants. Mycorrhizae were most effective in supplying Zn to plants early in the growing season, when plants are becoming established and have high nutrient demand to sustain plant growth.

Crop nutritional quality in relation to soil management:

The effect of soil management on mycorrhizae, plant nutrient uptake and nutrient concentration in fruits is being investigated on 3 organic and 6 conventional farms in the California Valley. Tomato plants were grown on each farm, soil and fruits were sampled and analyzed on each farm. Soil data analysis indicated significant management effects on soil chemical properties: soil pH and soil exchangeable Na and Ca were higher on organic farms whereas soil extractable Fe and Mn were greater on conventional farms. Even though there were no differences in soil extractable Zn, concentration of Zn in fruits was significantly higher on conventionally managed farms.

Soil microbial processes are important in organic production because these systems rely exclusively on organic sources of nutrients. AMF may be especially important for nutrient uptake in an organic production system because they increase the 'foraging' capacity of the root system. Another study was conducted on a research site using the mycorrhizal and non-mycorrhizal plants to evaluate the impact of conventional standard tillage and organic strip-till on root distribution, mycorrhizae, crop nutrient uptake and fruit quality in relation to availability of nutrients. The fields plots (1.5 ha of land) have been organically-managed at the UC Davis Vegetable Crops Field Facility for three years with frequent additions of composted manure and cover crop residues, for comparison with conventional management without cover crops and with inorganic fertilizers. At harvest root length density and mycorrhizal colonization were determined. Fruit color, firmness and compositional quality of fresh market tomato were analyzed for each genotype at the UC Davis Food Science laboratory. Vitamin A&C, lycopene, flavenoids and total phenolics were also determined. Data are currently being analyzed.