Nitrogen Mineralization from Crop Residues in the Pacific Northwest Irrigated Potato Cropping Systems A. K. Alva H. P. Collins W. L. Boge R. A. Boydston ABSTRACT. Transformation of organic nitrogen (N) in soil organic matter, and in crop residues, into inorganic forms (defined as N mineral- ization) allows N to be available to crop plants and/or subject to leaching losses. Estimation of N contribution from crop residues can help fine- tune fertilizer N application to minimize leaching losses. In potato pro- duction systems, wheat, field com, sweet com, and alfalfa are used as rotation crops. Nitrogen mineralized from these residues contributes to N supply forthe subsequent crop in rotation. In irrigated production sys- tems in the Pacific Northwest, the research indicated that the annual amount of N mineralized from soil organic matter and crop residue ac- counts for an annual average of 85,83,75,59, and 44 mg' kg- 1 for sweet com, alfal,fa, field com, wheat, and potato residues, respectively. The mineralized N during the May through August period accounted for 44 A. K. Alva (E-mail: aalva@pars.ars.usda.gov), H. P. Collins, W. L. Boge, and R. A. Boydston are affiliated with the USDA-ARS Vegetable and Forage Crops Research Unit, 24106 North Bunn Road, Prosser, WA 99350. Address correspondence to: A.. K. Alva at the above address. The authors would like to express their appreciation to AgriNorthwest Company, Kynnewick, WA, for providing the field site and for their cooperation with various field operations to conduct the long-term potato cropping systems research. The assis- tance of Tami Baugh, Marc Seymour, and Melanie Wilson for the field experiments and preparation of this manuscript is greatly appreciated. The study was funded in part by the Washington State Potato Commission. Journal of Vegetable Science, Vol. 11(4) 2005 Available online at http://www.haworthpress.com/web/JVS . doi: 1O.13001J484vlln04_05 47