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Title: USE OF 15N ISOTOPIC TECHNIQUES TO ASSESS THE POTENTIAL OF A MUSTARD COVER CROP TO CYCLE N TO POTATOES

Author
item Collins, Harold
item Delgado, Jorge
item Alva, Ashok
item Follett, Ronald

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2006
Publication Date: 7/7/2006
Citation: Collins, H.P., Delgado, J.A., Alva, A.K., Follett, R.F. 2007. Use of 15n isotopic techniques to estimate nitrogen cycling from a mustard cover crop to potatoes. Agronomy Journal. 99: 27-35, 2007.

Interpretive Summary: It has been reported that some areas of the Pacific Northwest U.S. were among areas with the greatest potential for groundwater impacts from NO3-N leaching. Farmers in the Pacific Northwest are using cover crops such as white and brown mustards in rotation with potatoes because it reduces potential wind erosion and serves as a biocontrol practice. However there is no information on N cycling from cover crop mustard to potatoes. We used a new 15N isotopic crop residue exchange technique to assess N cycling potential under field conditions. The mustard cover crop recovered 34 to 52% of the 56 kg 15N fertilizer applied. The total yield and N uptake by the cover crop ranged from 4.6 to 7.5 Mg ha-1 and 92 to 142 kg N ha-1, respectively. About 29 % of the N in the cover crop was cycled and absorbed by the following potato crop. The N contained in mustard cover crops supplies 30 to 40 kg N ha-1 to succeeding potato crops. The cover crop reduces N losses in irrigated potato systems, increases nitrogen use efficiency (NUE) and sequesters N in the soil organic fraction of sandy soil systems.

Technical Abstract: It has been reported that some areas of the Pacific Northwest U.S. were among areas with the greatest potential for groundwater impacts from NO3-N leaching. Farmers in the Pacific Northwest are using cover crops such as white and brown mustards in rotation with potatoes because it reduces potential wind erosion and serves as a biocontrol practice. However there is no information on N cycling from cover crop mustard to potatoes. There is the need to assess the N cycling from the cover crop mustard to the potato. We used a new 15N isotopic crop residue exchange technique to assess this N cycling potential “in situ”. Two two-year 15N field research studies were conducted at the USDA-ARS Paterson, WA research site on a Quincy sandy (Xeric Torripsamments) soil containing 0.4% SOM under sprinkler irrigation. The established rotation at the site was a winter wheat (Triticum aestivum L.) - sweet corn (Zea mayes L.)- sweet corn – potato (Solanum tuberosum L.) rotation. We established two 15N field research plot studies from 2002 to 2004 to assess the potential of N cycling from cover crop mustard (Brassica hirta) to potato. The mustard cover crop recovered 34 to 52% of the 56 kg 15N fertilizer applied. The total yield and N uptake by the cover crop ranged from 4.6 to 7.5 Mg ha-1 and 92 to 142 kg N ha-1, respectively. About 29 % of the N in the cover crop was cycled and absorbed by the following potato crop. There is the potential to budget 30 to 40 kg N ha-1 in the cover crop as a source for N to the potato. The cover crop will contribute to reduce the N losses in irrigated potato systems, increase nitrogen use efficiency (NUE) and sequester N in the soil organic fraction for these sandy soil systems.