Soil testing after small grains is well underway, and we are seeing much variability in residual soil nitrate after wheat. Crop yields have varied from below average to well above expectations in the same area. Planting date, hot or cool weather, and rainfall (too little or too much) were major factors this year.
The major factors influencing the amount of residual soil nitrate-nitrogen after crops are:
- Fertilizer nitrogen rate: too high or too low
- Crop yield achieved: much lower or higher than expected
- Soil nitrogen losses: denitrification and leaching after too much rainfall
- Soil nitrogen mineralization from organic matter: cool or warm growing season
AGVISE has tested over 10,000 soil samples from wheat fields across the region. The table below shows the percentage of soil samples in each soil nitrate category for several areas of Manitoba, Minnesota, Montana, North Dakota, and South Dakota. The data should give you a general idea of how variable residual soil nitrate is from field to field in each region. With such variable crop yields, there is quite a bit of variability in residual nitrate following wheat in the region. In the drought-affected areas of the region, over 10-30% of soil samples have more than 60 lb/acre nitrate-N (0-24 inch) remaining after wheat.
On Prevented Planting fields, the factors above, plus some additional factors listed below will affect the amount of residual soil nitrate-nitrogen.
- How long was water standing on field?
- Was weed growth controlled, early or late?
- Was tillage used? How many times? How deep?
- Was a cover crop planted? What amount of growth was achieved?
When submitting soil samples from fields that were not planted, please choose “Fallow” or “Cover Crop” as the previous crop. This will allow us to send additional information on the soil nitrate trends for Prevented Planting fields once we get enough data.
If you have any questions, please call our experienced technical support team of agronomists and soil scientists.