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Title: TRACING THE FATE OF 15N IN A SMALL-GRAIN POTATO ROTATION TO IMPROVE ACCOUNTABILITY OF N BUDGETS.

Author
item Delgado, Jorge
item DILLON, M - CSU
item SPARKS, R - USDA-NRCS
item Follett, Ronald

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2003
Publication Date: 12/14/2004
Citation: Delgado, J.A., Dillon, M., Sparks, R., Follett, R.F. 2004. Tracing the fate of 15n in a small-grain potato rotation to improve accountability of N budgets.. Journal of Soil and Water Conservation. 59:271-276.

Interpretive Summary: Our objective for this paper is to present the concept that N budgets and N cycling are an important part of increasing efficiencies, yields and quality. Traditionally, because of the large C/N ratios, the small grains do not get credited with potential to cycle N. This study shows the importance of accounting for N cycling in nutrient management practices, as is already being done by practicing agronomists. It is recommended budgeting 11 kg N ha-1 from barley or 5 kg N ha-1 from wheat crop residue when incorporating crop residues during the Fall, in small grain - potato rotations. Our study also agrees with previous studies that found that the incorporation of high crop residue from small grains increases the N levels in the soil organic matter. We found that after two years of N fertilizer additions, we recovered about 28 to 35% of the applied N in the soil compartment, most likely bound in the particulate organic matter. Small grains contribute to water conservation by scavenging NO3-N from residual soil, background irrigated water, and contributing to sequester N in the soil organic fraction or irrigated sandy soil systems.

Technical Abstract: Nitrogen is one of the most difficult elements to manage because of its dynamics and mobility. To maximize its use efficiency, we need to increase the accountability of N budgets accessing N sources and sinks. Although we have the potential to implement best nutrient management practices that will minimize net NO3-N leaching losses from small grain [barley (Hordeum vulgare L) and wheat (Triticum aestivum L)]-potato (Solanum tuberosum L) systems, we need to continue improving N use efficiency and accountability of the N cycling from small grain crop residue into potato crop. This pathway is frequently assumed to be zero and is not commonly budgeted. We used 15N labeled fertilizer in this unique crop residue exchange study to trace the 15N crop residue into a potato crop. We found that the 15N recovery by these small grains was about 46%. When we factored in the residual soil 15N , the average 15N was about 70%. The cycling of N from the crop residue into the potato averaged about 9 kg N ha-1 for wheat and 12 kg N ha-1 for barley. There is potential to account for this N cycling from the crop residue in the Fall to fine tune the assessment of N budgets for commercial small grain-potato operations. Agronomists are currently incorporating this accountability into their N budget practices.