Finding your limiting factor isn’t as obvious as just looking at a soil sample or even a tissue sample and adding whatever is lowest. I’ve looked at a soil sample and saw that there was plenty of something, but when we dove in deeper with a tissue sample it showed a deficiency multiple times throughout the year. A very common example of this is Phosphorous tying up Zinc. You may seem to have high enough levels of Zinc in a soil sample, yet on a tissue sample you come in below your threshold time after time. As your Zinc gets tied up your plants ability to maximize water usage drastically diminishes. I haven’t seen an example of the reverse where a Zinc seed treatment ties up Phosphorous, but considering they compete against each other I imagine it’s possible.

The other major one that I want to discuss is high Magnesium levels tying up Nitrogen. I’ve talked about base saturation in a previous blog, but I haven’t gotten to dive into what optimum levels that I look for. High Magnesium levels typically means heavy clays. That makes it harder for roots and water to penetrate. In a plant, Magnesium is located at the center of the chlorophyll. Nitrogen attaches to it within the plant. Nitrogen attaches to Magnesium the same way when it is outside of the plant in your soil. So, as your soils get “overloaded” with Magnesium you tie up Nitrogen and lose yield. At a base saturation of 10-12% you have almost a 1:1 pound of Nitrogen to bushel of corn ratio. As your Magnesium levels rise, the efficiency drops. At just 20% you need almost 1.5 lbs. of Nitrogen for a bushel of corn. (It can vary depending on CEC levels of your soil).

A correlation that is common to see is excess Nitrogen tying up Copper and Potassium. This can lead to weak stalks and the inability to fight off disease later in the year. Another one to look out for is Sodium tying up Potassium and Calcium. If your levels of Sodium are higher than Potassium you won’t be able to grow anything. Rarely do I see this issue but it’s something to look for along road ditches or really scald spots in a field.

Unfortunately, when raising a top crop, it isn’t as simple as finding what’s lowest in a soil sample and adding it. While that’s a good start, we need to make sure that we monitor how it’s all correlating throughout the year. If you have too much of something, you don’t have enough of something else.