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Nitrogen Status in 2021 Corn Fields

OMAFRA Field Crop staff lead an annual PSNT survey across Ontario to measure nitrate mineralized from the soil as an indication of year-to-year soil nitrogen supply. Each spring, 80-100 soil samples are collected from fields that have not received N. Samples are collected just prior to traditional sidedress time, typically V3-V4 stage.

PSNT Survey

Nitrogen mineralization is favoured by warm soil temperatures with adequate soil moisture and aeration. Excess moisture can slow mineralization or increase the potential for losses through denitrification (especially under warm conditions) or leaching.

Spring of 2021 progressed similar to 2020. Sunshine and little rainfall produced great soil conditions through April and May. A period of cold temperatures dominated for a 1-2 week period early May, which was followed by seasonal to above seasonal temperatures . Variability in temperatures brought into question how N mineralization may be affected in 2021.

From May 31 to June 2, 93 samples were collected across Ontario from a range of previous crops, soil textures and geographies. A V3-V4 stage is typically targeted for PSNT sampling, but given the start of sidedressing and warm temperatures in the forecast, the survey was slightly ahead of schedule with most corn ranging V1-V3. Where corn fields without preplant N could not be found, soybean or processing vegetable fields were sampled if rotations were representative of grain corn (following wheat or soybeans).

Survey Results

The average PSNT value for the 2021 survey was 13 ppm. This is similiar to 2020 (14 ppm) and slightly above the long-term average of 12 ppm (2011-2020, Fig 1) suggesting similar to slightly higher than normal mineralization by sidedress stage in 2021. For historical reference, these levels compare most to years 2012, 2018 and 2020 (Fig 1). The 5 point lines in Figure 1 reflect a previous GFO funded project at 25 farms where soil N samples were collected throughout the spring. Years with single points reflect the traditional provincial soil N survey where single sampling times target the V2-V4 crop stage.

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