ISSN 2285-5785, ISSN CD-ROM 2285-5793, ISSN ONLINE 2285-5807, ISSN-L 2285-5785


Published in Scientific Papers. Series A. Agronomy, Vol. LX
Written by Dan SULLIVAN, Nick ANDREWS

Satisfying crop nitrogen (N) requirements efficiently in organic agriculture requires an accurate estimate of plantavailable N (PAN) release from organic inputs. PAN is the sum of the mineral N present in the organic material at the time of application, plus net N mineralized (sum of NH4-N and NO3-N) in soil. We verified several regression equations for accuracy in predicting PAN release from organic inputs (manures, composts, and cover crop residues) for summer vegetable crop production in the Willamette Valley of Oregon, USA. An Excel spreadsheet version of the regression equations was prepared and is distributed online as the Oregon State University (OSU) Organic Fertilizer and Cover Crop Calculator. Using the Calculator requires the user to specify the organic input application rate, its total N concentration (dry matter basis), and whether the organic input is fresh or composted. We verified the accuracy of the Calculator equations via aerobic incubation of organic inputs in moist western Oregon soils in the laboratory (sandy loam, loam, or clay loam textures; pH 5.5 to 6.5; 20 to 25oC). Fertilizer equivalency trials, where PAN from organic inputs was determined relative to PAN from mineral N fertilizers, were also used to verify Calculator predictions. Outreach publications have been developed to accompany the Calculator, in order to explain its function and to encourage farmers and farm advisors to use it.

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