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Nitrogen Status in 2020 Corn Fields

  • Pre Sidedress Nitrogen Test (PSNT) soil samples were collected from 94 sites across the province from June 8th to 10th, 2020
  • The average PSNT value was 14 ppm, slightly above the long-term average of 12 ppm.
  • Optimal nitrogen (N) rates are a function of both soil N supply and yield. Consider both when determining N rate requirements in 2020.
  • PSNT survey results are a general indication of soil N status, not a substitute for actual sampling.
Background
 
OMAFRA Field Crop Unit staff have traditionally led an annual Pre Sidedress Nitrogen Test (PSNT) survey across Ontario at the beginning of June to measure soil nitrate mineralized from the soil as an indication of year-to-year soil nitrogen status. In past years, 80-100 samples would be collected from fields across the province that had not yet received nitrogen. Soil samples are collected when corn has generally reached the V3-V4 stage, just prior to traditional sidedress time.
 
PSNT Survey
 
Nitrogen mineralization is favoured by warm soil conditions with adequate soil moisture and aeration. Excess moisture, especially under warm temperatures, can slow mineralization, or increase the potential for losses through denitrification or leaching.
 
The spring of 2020 arrived relatively early. With sunshine and very little rainfall, soil conditions were generally great through April and early May. A period of record cold temperatures dominated for a 1-2 week period mid-May, which was followed by a couple weeks of seasonal to well above seasonal temperatures. Variability in temperatures on both extremes brought into question how N mineralization may be affected in 2020.
 
A total of 94 samples were collected from across the province, representing a range of previous crops, soil textures and geographies of Ontario. Samples were collected from June 8-10 for a V3-V4 stage target sampling. Due to variability in rainfall and planting dates, crop stage ranged from V1 to V5. Where corn fields without preplant N could not be found, soybean fields were sampled if rotations were representative of grain corn (following wheat or soybeans).
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