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Title: NITROGEN MINERALIZATION FROM DIFFERENT CROP RESIDUES IN THE PACIFIC NORTHWEST IRRIGATED POTATO CROPPING SYSTEMS

Author
item Alva, Ashok
item Collins, Harold
item Boge, William
item Boydston, Rick

Submitted to: Journal of Vegetable Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2005
Publication Date: 11/10/2005
Citation: Alva, A.K., Collins, H.P., Boge, W.L., Boydston, R.A. 2005. Nitrogen mineralization from different crop residues in the pacific northwest irrigated potato cropping systems. Journal of Vegetable Science. Vol 11: 47-59. 2005.

Interpretive Summary: Nitrogen is an important nutrient for crop growth, which can be applied as inorganic fertilizer and/or organic soil amendments. The organic form of nitroen is not readily available to the plants, hence, it needs to be transformed into inorganic forms primarility into ammonium and nitrate forms. These latter forms are readily available to plant uptake. During the production of most annual crops, the crop residues, i.e. straw, roots, etc. are returned to the soil. The nitrogen in the crop residues undergoes similar transformation as explained above and becomes available to the subsequent crop. This is important in a potato rotation system, which is typically corn-potato-wheat sequence in the Pacific Northwest. The mineralized N from the previous crop residue contributes to nitrogen requirement of the crop in question. In this three year study, nitrogen mineralization was evaluated on an annual basis. The three years mean data showed the annual amounts of nitrogen mineralization from sweet corn, alfalfa, field corn, wheat, and potato residues were 85, 83, 75, 59, and 44 mg/kg, respectively. The nitrogen mineralized during May through August contributed 44 to 58 percent of total annual nitrogen mineralization from among different crop residues. The soil moisture and temperature conditions during the May through August period are optimal for nitrogen mineralization. This study also showed a positive correlation between the soil temperature and rate of nitrogen mineralization. A clear understanding on the pattern and rate of nitrogen mineralization is important to fine tune the nitrogen requirement of a given crop in the rotation sequence.

Technical Abstract: Transformation of organic nitrogen (N) in soil organic matter and in crop residues into inorganic forms (defined as N mineralization) renders this N available to crop plants and/or subject to leaching in the soil with water front. Estimation of N contribution from crop residues is important to determine the crop N requirement in an effort to finetune N application to minimize excess application that may lead to leaching losses. In potato production systems, wheat, field corn, sweet corn, and alfalfa are used as rotation crops. Depending on which crop is in rotation, after the product of economic value is harvested, residue of the crop is incorporated. Nitrogen mineralized from this residue contributes to N requirement of the subsequent crop in rotation. This study showed in predominantly irrigated production systems in the Pacific Northwest, the annual amounts of N mineralized from soil organic matter and crop residue accounts for 85, 83, 75, 59, and 44 mg/kg for sweet corn, alfalfa, field corn, wheat, and potato residues, respectively. The mineralized N during May through August period accounted for 44 to 58 percent of total annual N mineralization for the above crop residues. This period represents the ideal temperature and soil moisture conditions for maximum mineralization. This is also a period of active plant growth, thus, plant uptake of mineralized N can be maximum during this period. The in-situ technique adapted in this study provided a convenient method to measure the N mineralization by maintaining the soil moisture and temperature conditions in the incubation columns nearly similar to those in the bulk soil.