Biofuel and Other Agricultural Co-Products As Soil Amendments in a Potato Rotation in Pacific Northwest.

The state and federal targets for increased biofuel production will likely result in an abundance of co-products, i.e. seed meals of canola (CAN_M) Camelina (CAM_M), and Mustard (M_M) as well as dry distilled grain (DDG). Biogas production from animal manure by anaerobic digestion results in an abundance of fiber (ADF) as co-product. Steam distillation of mint stem and leaves to extract oil leaves substantial vegetative residue (MINT_R). A feasible and beneficial avenue to utilize the co-products is by soil amendment at high rates as sources of plant nutrients and/or to improve soil quality as well as productivity. A two-year field study was conducted to evaluate the effects of application of the co-products to a sandy soil under a potato rotation system with center pivot irrigation. The products are broadcasted prior to tillage at a target rates of 224, 336, and 448 kg N ha^-1, as compared to 112 kg N ha^-1 as urea. Assuming 50% of total N in the co-products is mineralized and plant available at the first cropping season, the low application rate is equivalent to industry standard pre-plant N application of 112 kg N ha^-1 as Urea. The high treatment rates are considered as potential disposal rates to evaluate any negative effects of high rate applications. All treatments received 224 kg ha^-1 in-season N as UAN (32% N) in five applications at 2 weeks interval which began 4 weeks after emergence. The tuber yields significantly increased across both years with application of seed meals or DDG as compared to the industry standard N management practice. Yield response to ADF was rather marginal, and only observed at the 336 and 448 kg N ha^-1 rates. No favorable response was evident with application of MINT_R. The nutrient carryover effects on subsequent and rotation crop was evaluated on corn response.