Tracing the fate of 15 N in a small-grain potato rotation to improve accountability of nitrogen budgets

Nitrogen (N) is difficult to manage because of its dynamic nature and mobility. Improving N use efficiency in agricultural production requires better accounting of N sources and sinks. In small grain [barley (Hordeum vulgare l.) and wheat (Triticum aestivum l.)]-potato (Solanum tuberosum l.) systems, N cycling from small grain crop residue into potato crops is poorly understood. We used 15N labeled fertilizer to trace N from the small grain crop residue into a potato crop. We found that the 15N recovery by these small grains averaged about 46 percent. When we factored in the soil 15N recovery, the average 15N recovery in the system was about 70 percent. The cycling of N from the crop residue into the potato averaged about 2.6 kg N ha−1 for wheat and 4.4 kg N ha−1 for barley. We estimate that the total N cycling from the above ground and below ground compartments was about 4 to 9 kg N ha−1 and that total N released from the crop exchange residue, including the unaccounted N, was about 9 kg N ha−1. About 82 to 86 percent of the N that was incorporated with the crop residue was still in the system (soilcrop) after one year of cycling, which suggests that considerable N is sequestered in the soil over that time period. Results highlight the importance of crop residue in N cycling and identify opportunities to improve the assessment of N budgets for commercial small grain-potato operations.