Thursday, 10 November 2005 - 8:30 AM
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Contribution of Organic N Fertilizers and Irrigation to Plant and Soil N Availability on Organic Broccoli Farms in Central and Coastal California.

Sajeemas Pasakdee1, Gary Banuelos2, Weixin Cheng1, and Carol Shennan3. (1) Dept. of Envi Studies, U of CA Santa Cruz, USDA-ARS-WMR, 9611 S. Riverbend, Parlier, CA 93648, (2) USDA-ARS-WMR, 9611 S. Riverbend, Parlier, CA 93648, (3) Center for Agroecology & Sustainable Food Systems, U of CA Santa Cruz, 1156 High St., Santa Cruz, CA 95064

Multi-year studies examined the effects of different organic N fertilizers and water application rates on broccoli yield, N dynamics in plant and soil, and soil water content on organically-grown broccoli fields in Central Coast and Central Valley regions of California. Irrigation treatments at 80, 100, or 150% Etc were applied to each organic N fertilizer treatment based on crop evapotranspiration rate (Kc) and a weekly weather data reported by California Irrigation Management Information System (CIMIS). Organic fertilizer treatments were as follows; a pre-planting compost application of 140 kg N ha-1, and compost and three different organic N fertilizers [fish powder, Phytamin (bloodmeal and feathermeal mix), and seabird guano] added twice as a side dress (for a total of 112 kg N ha-1). The influence of form of organic fertilizer, rate of irrigation water, and their interactions was detected in these studies. Excessive rainfall at both locations minimized the full impact of water treatments. Broccoli biomass (leaf, stem, and floret) increased significantly from additional organic N fertilizer applications compared to adding ‘compost only' on both field sites. Average levels of soil nitrate were higher than soil ammonium levels at the 0-15 cm, 15-45 and 45-90 cm depths for all treatments, and total soil N concentrations are being analyzed. Overall higher levels of soil water content were observed at the Central Valley field site (clay loam soil) compared to Central Coast field site (sandy loam soil). In addition, soil water content was higher at deeper depths at both field sites; however, there was no significant difference among organic fertilizer treatments. Total N concentrations in leaf tissue and nitrate concentrations in leaf blade (petiole) were significantly higher in treatments receiving additional organic fertilizers than the ‘compost only' treatment.

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