Does Soil Nitrate Testing Pay?

If you found a $5 bill on the street, would you pick it up? I am pretty sure I would!

A simple analogy is sometimes needed to help people see the forest through the trees. We all know that soil testing is a valuable tool, but we occasionally forget how big that dollar value can be. A small difference of 10 lb/acre nitrate-N in the soil nitrate test can easily translate to $5.00/acre in nitrogen fertilizer, application, and logistic savings for next year’s crop.

The amount of residual soil nitrate is trending a little less than historical averages in some areas, while others are running higher than normal. The regional and seasonal differences are caused by agronomic and environmental factors that are hard to predict (e.g. crop yield and nitrogen use, fertilizer nitrogen rate, soil nitrogen losses, nitrogen mineralization from soil organic matter). Collecting a soil sample is the only accurate way to know what remains in the soil profile, giving you a starting point for next year.

I recently had a phone call from a farmer who was looking at some soil test results with very low residual soil nitrate-N levels. He was questioning if soil nitrate testing was really worth it, if not much nitrate-N was found in some fields. I pointed out that if he had not run the soil nitrate test, he would not have known that he needed to apply MORE nitrogen than normal for next year’s crop. He would have assumed too much nitrogen remaining in the soil and missed the targeted crop yield he wanted to achieve.

I spent some time looking through other soil test results with the farmer. We soon discovered that his soil test results had a range of over 30 lb/acre nitrate-N across his fields. For each 10 lb/acre nitrate-N found in the soil nitrate test, it can save $5.00/acre in fertilizer costs at current urea prices. The cost of soil testing was easily covered with the nitrogen fertilizer savings alone. As a bonus, the farmer gained valuable knowledge about other soil nutrients such as phosphorus, potassium, sulfur, zinc, etc.

I also know some people try to utilize local average soil test values in their fertilizer rate calculations. I always caution people because there is a lot of variability behind that average value. For example, one local zip code area has 40% of soil samples after wheat between 21 to 40 lb/acre nitrate-N (0-24 inch). Another 40% of soil samples has over 40 lb/acre nitrate-N remaining. For 2 in 5 fields, there is another $25 to 55/acre in fertilizer nitrogen savings to be revealed though a soil test compared to the local average. Another 1 in 5 fields requires 20 lb/acre MORE nitrogen fertilizer than the local average would imply; the cost of underapplying is more expensive than overapplying because you also lose crop yield. If you had 5 fields and only used the local average, you’d get the right fertilizer rate on 2 fields, overapply on 2 fields, and underapply on 1 field. The variability is where the risk lies.

I do not know about you, but I would be that guy who picks up the $5 bill on the street every time. Soil nitrate testing is a smart investment that helps me know that I am applying the right nitrogen rate to maximize crop yield and profitability without undue risk to the environment.