Abstract
ABSTRACT The N benefits attributed to legumes in crop rotations are often overestimated because the technique for quantifying this benefit without 15N includes rotation effects not directly related to N. This study was conducted to test an approach proposed in the literature for delineating such effects without requiring the use of 15N. Potato (Solanum tuberosum L. cv. Norwis) was grown continuously and in two-year rotations with alfalfa (Medicago sativa L. cv. Nitro), hairy vetch (Vicia villosa Roth), or white lupin (Lupinus albus L. cv. Ultra). Potato was fertilized with 0, 90, or 180 kg N ha−1 as (NH4)2S04. The total, N, and non-N effects of crop rotation were calculated based on tuber dry weight and plant N uptake for the rotation systems and the tuber dry weight vs. plant N uptake relationship for continuous potato. The total effect of crop rotation generally declined upon increasing N fertilizer from 0 to 90 kg N ha−1, apparently due to decreasing importance of the N effect with added fertilizer. Non-N related effects mostly remained static across fertilization regimes. Those effects attributed to N generally declined upon adding 90 kg N ha−1 in a relatively dry year; and upon adding 90 and 180 kg N ha−1 in a year with more favorable precipitation. Calculated N effects with no N fertilizer reflected the quantity and quality of legume crop residues. This method does allow assessment of total, N, and non-N related rotation effects. However, the approach appears sensitive to climatic conditions, and data should only be subjected to analysis where a yield response to N exists.
Published Version
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