This fall and winter I’ve had the pleasure of viewing hundreds of soil tests across Eastern Manitoba and one fairly common trend seen by myself and my dealers was slightly higher than expected residual soil nitrate levels especially on fields grown to wheat, a major crop in the region. We were fortunate enough to harvest a fairly high yielding wheat crop with higher than average protein as well so it was a bit of a surprise when this is what we observed. This observation though lines up with what a large soil test company I deal with found as well. On over 25,000 wheat fields they tested this fall, the average soil nitrate was 40 lbs/acre. Compared to the last 30 years, that number isn’t that high but compared to the last few years, it stands out a bit. Some factors that they and I believe lead to this include:

1. Growers put down more nitrogen than usual in 2015. We found in 2014 in Manitoba we had tremendous yields but very low protein in our wheat which limited marketing opportunities for a lot of growers including the ability to haul wheat south into the USA where protein spreads are much higher. Because of this, growers didn’t skimp on nitrogen this past spring.
2. Wheat yields were high but not quite as high as 2014. We had some hot weather in mid-summer that may have limited our wheat yields when crops were filling. These lower yields led to higher protein but also caused there to be less total N uptake, leaving more residual N in the soil.
3. The very warm summer also resulted in more nitrogen mineralization in the soil as well. Most of this mineralization occurred too late in the summer for the wheat plant to use the nitrogen so it remained in the soil as residual soil nitrate.
4. The biggest and final reason we found was that growers did not have large N losses caused by very wet soil conditions when the soils were warm this year. Some years (or most years lately) we get a lot (and by a lot, I mean too much) of rainfall in June (usually right when we want to and need to be spraying herbicides!) and this causes warm, saturated soils and denitrification in heavy soils and leaching in light soils. This year that didn’t occur so our crop got to use more of the actual nitrogen we put down.

All of these factors add up and caused there to be a little bit more residual soil nitrate than usual and that’s definitely not a bad thing. Again though this is just a general trend and every field and situation is different. We encourage growers to still soil test every field, every year as this is truly the only way to know how much nitrogen you have left as well as all the other essential soil nutrition information you get from the soil test as well. Without this knowledge, you truly are just playing guesswork in terms of fertilization and soil nutrition and starting the year off behind.

Remember the key to a great crop starts with knowing what is in your soil!

Shane Falk

DSM, Eastern Manitoba