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The Pre-Sidedress Nitrogen Test for Corn: Will It Really Work On Our Highly Variable Fields in Central Ontario?
Quinte Region Soil and Crop Improvement Association Project
- In three of the five sites within this project in 2001 the PSNT predicted actual N requirements relatively accurately; within 29 lbs N/acre at the Bickle Site, and within 12 lbs N/acre at the CroWe and Greydanus Sites. In year one (2000) of the study 2 of the 3 locations showed good predictive ability for the N test, At the two of the three locations over the course of the study, PSNT recommendations and yield response data were not reliably connected, principally due to the dry weather conditions that caused very low corn yields (all less than 60 ba/ac).
- There appeared to be relatively little risk of the PSNT recommending low N rates that would result in significant crop yield loss.
- Soil nitrate levels, as determined by soil sampling in the pre-sidedress window, appeared to have a manageable level of variability. One exception in this was the Crowe site were significant point to point variability existed. Blocking the fields into long narrow replications generally resulted in PSNT values that were within 10-15 % of the average. It appeared that simple combined samples from a uniform sampling pattern across the field gave a reasonable N rate prediction. We cannot rule out however that there are fields within the Quinte region that may have more variability than the ones used in this study.
- Soil sampling procedure for the PSNT must be followed with particular attention to the following points:
- do not sample in starter fertilizer bands
- samples must be 12 inches deep (not the traditional 6 inch fertility sample)
- The results of this project hold promise for the use of the PSNT in the region. It will not always be a bulls-eye approach to nitrogen management but it generally gives good direction to the farmer. In the cases where corn yields were abnormally limited by dry weather, nitrogen demand is also very low and therefore will not correlate to PSNT recommendations (or other estimates of N requirement, either)
- Greater economic savings may be likely for growers who use the PSNT test to identify high residual nitrate concentrations due to legume forages and/or manure applications.
Appreciation is expressed to the following for participation in this project.
Ontario Soil and Crop Improvement Association
OMAF Crop Technology
Greg Stewart, Corn Industry Program Lead, OMAF