/AnMtgsAbsts2009.52079 Comprehensive Perspective On the ISNT Approach.

Tuesday, November 3, 2009: 2:30 PM
Convention Center, Room 414-415, Fourth Floor

Quirine Ketterings, Animal Science, Cornell Univ., Ithaca, NY, Jonathan Klapwyk, Pride Seed, Guelph, ON, Canada, Joseph Lawrence, Cornell Coop. Ext., Lewis County, Lowville, NY and Karl Czymmek, Department of Animal Science, Cornell Univ., Ithaca, NY
Abstract:
High fertilizer prices and awareness of the environmental implications associated with over-application of nutrients have increased the need for reliable predictions of nitrogen (N) applications for corn (Zea mays L.). Soil testing has long been the basis for P and K guidelines but for N, a yield-based N recommendation approach with adjustments for rotations and manure use has predominated for several decades. Such a yield-based approach is likely to result in under or over-fertilization since soil N supply is not taken into account. The Illinois Soil Nitrogen Test (ISNT) was developed as a quick and simple alternative for determining soil N supply potential. Since its release in 2001, several research groups have evaluated the ISNT as a tool for identifying the N responsiveness of corn. These studies have shown mixed results. Careful evaluation of the literature and an understanding of N cycling reveal why such contrasting results are not surprising: the ISNT approximates ammonium-N and soil N supply potential from labile organic N whereas crop responsiveness to N fertilizer and optimum N rates depend on timing and amount of soil nitrate-N available compared to crop N needs. As the ISNT does not measure nitrate, ISNT-N alone cannot be used to predict total N availability. Nor will it be successful in determining N needs of corn across diverse agricultural rotations and nutrient management systems. However, New York research showed that when ISNT-N results were interpreted as estimation of potential soil N supply, and when critical values were adjusted based on the soil’s overall organic matter content (LOI), the ISNTxLOI combination was 84% accurate in predicting if sidedress N was needed for 2nd or higher year corn. The project included nine responsive and ten non-responsive sites, indicating great potential for N fertilizer savings with ISNT-adjusted corn nitrogen management.