Research report to the Oregon Processed Vegetable Commission
PI Ed Dan Sullivan
OSU Dept. of Crop and Soil Science
Co-PI Aaron Heinrich
OSU Dept. of Horticulture
The market for organic vegetables is increasing. As conventional farmers transition fields to organics to meet this demand, there is a need for better organic nutrient management guidance, especially for nitrogen (N). Organic N management is more challenging than conventional N management due to a higher level of uncertainty surrounding the N supplying capacity of an organically managed soil as well as the constraints of organic fertilizers (supply, application timing and placement, and uncertainty of release rate and amount). As a result, conventional nutrient management strategies may not be appropriate for organically managed systems. With organic N management there is often a higher risk of excessive nitrate-N loss and higher risk of not achieving economic yield targets.
Results of the first year of this project demonstrate the nutrient management challenges that organic producers face, as well as potential solutions. Of the seven fields sampled in this study, soil test P was elevated in five (>90 ppm Bray 1P). Although the probability of a P fertilizer response is very low for these high soil test P fields for all vegetable crops, an average of 178 lb P2O5/acre was applied. This was the result of applying low N:P ratio fertilizers (mostly pelleted and raw chicken litter) to meet N demands. There is little incentive to switch to N only fertilizers such as feather meal (FM) due to its high cost (approximately $5-6 vs. $7-8 per lb of plant available nitrogen (PAN) from pelleted chicken manure and FM, respectively). PAN from leguminous cover crops is often the least expensive source of organic N, however, cover crops are not always compatible with every farming system.