Illinois Soil Nitrogen Test with Organic Matter Correction for Predicting Nitrogen Responsiveness of Corn in Rotation
- J. R. Lawrencea,
- Q. M. Ketterings *b,
- M. G. Golerc,
- J. H. Cherneyd,
- W. J. Coxd and
- K. J. Czymmeke
- a Nutrient Management Spear Program, current address: Cornell Cooperative Extension of Lewis County, 5274 Outer Stowe Street, P.O. Box 72, Lowville, NY 13367
b Nutrient Management Spear Program, Dep. of Animal Science, Cornell Univ., 323 Morrison Hall, Ithaca, NY 14853
c Nutrient Management Spear Program, Dep. of Animal Science, Cornell Univ., Ithaca, NY 14853
d Dep. of Crop and Soil Sciences, Cornell Univ., Ithaca, NY 14853
e PRO-DAIRY, Cornell Univ., Ithaca, NY 14853
Several research groups have evaluated the Illinois soil N test (ISNT) as a tool for identifying the N responsiveness of corn (Zea mays L.). These studies have shown mixed results. Research in New York improved the ISNT accuracy by adjusting the critical ISNT value (0–20-cm depth) for organic matter estimated by loss-on-ignition (LOI), resulting in an ISNT × LOI curve above which corn tended to be nonresponsive. We conducted 34 N rate trials (2005–2007) to further evaluate the accuracy of the ISNT × LOI curve in predicting the N responsiveness of corn in rotation with grass–legume sod or soybean [Glycine max (L.) Merr.]. First-year corn did not respond to sidedress N (16 trials), yet the ISNT × LOI curve predicted that sidedress N was needed for six sites. For second-, third-, or fourth-year corn after sod and corn after soybean, the ISNT × LOI curve accurately predicted N responsiveness for 15 of 18 sites (eight responsive and 10 nonresponsive sites). The ISNT values of first- and second-year corn were closely correlated (ISNTYear2 = −12.8 + 1.1 ISNTYear1, r 2 = 0.96, P < 0.001). The results of laboratory and field trials on ISNT dynamics from spring sod plowdown through sidedress showed an ISNT peak 1 to 4 wk after plowdown, indicating that samples taken at or after sidedress do not reflect sod N credits. We conclude that the ISNT × LOI curve accurately identified nonresponsive sites as long as the sample was not collected within 5 wk of sod plowdown and that sod N credits need to be taken into account for first-year corn.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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