Use of the Nitrate Soil Test to Predict Sweet Corn Response to Nitrogen Fertilization1
- S. Roberts,
- W. H. Weaver and
- J. P. Phelps2
A precise procedure for routinely interpreting soil test NO3 as a fertilizer guide should help achieve more efficient use of N on crops with a high N requirement. The present study was designed to calibrate soil test NO3 for predicting relative (percent of maximum) yield and the N-requirement index (NRI) of sweet corn (Zea mays L.) using Mitscherlich-type functions. The total N fertilizer requirement for the crop was equated to the potential yield increase multiplied by the NRI.
The NRI was calculated from N rate studies as the amount of N required per unit increase in sweet corn yield. ‘Stylepak’ sweet corn was grown 2 years in a row at a Warden silt loam (Xerollic Camborthids) site with rates of NH4NO3 the first year to give 84, 168, 252, 336, and 504 kg N/ha and a carry-over of from 10 to 70 ppm N the second year. Functions showed a range from 10 to 40 ppm soil NO3-N was correlated with relative yields ranging from 62 to 98% of maximum and the NRI's range from 26 kg N/ton of yield increase up to 98 kg N/ton. It was concluded that with as low as 10 ppm NO3-N, the potential yield increase multiplied by the NRI equated to a requirement of 251 kg N/ha. A soil test of 40–50 ppm NO3-N correlated with 98–99% of maximum yield and indicated little or no fertilizer was needed. The NRI soil testing approach has definite advantages because it eliminates the controversial practice of calculating a fertilizer equivalent from soil NO3 and fertilizer requirements can be calculated to fit different yield potentials of localized soil and cropping conditions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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