By Darren Hefty
Is there something wrong with your crop fertility program? Did you put on enough Potassium or Phosphorus this year? Let’s face it, those are questions most of us don’t want to think about very long. They make us uncomfortable. Why? Well, the answer is we don’t know for sure what our fertility programs are lacking until we either see poor yields in the fall or strange-looking plants during the summer. Since we’re in the middle of the season right now, here’s your chance to SEE nutrient deficiencies and DETERMINE what they are so you can fix them.
The most common nutrient deficiencies you’ll see on the lower leaves of your plants are Nitrogen, Phosphorus, and Potassium. The reason these deficiencies show up on the lower leaves of corn plants is because they are mobile nutrients within the plant. As the plant adds new growth, it will rob mobile nutrients like N, P, and K from the lower parts of the plant if it doesn’t have enough of those nutrients. Here’s how you tell them apart.
- Nitrogen – yellowing starts at the tip of the leaf and moves in a “v” shaped pattern down the mid-rib of the leaf when severe deficiency is present.
- Phosphorus – typically shows severe deficiencies by a purpling of the lower leaves.
- Potassium – yellowing starts at the tip of the leaf and moves down along the outside edges of the leaf when severe deficiency is present.
If you have yellowing on the upper leaves of the corn plant due to a severe nutrient deficiency, that indicates a shortage of immobile nutrients in the plant. Once the immobile nutrients become part of a leaf, they stay there. In other words, when the new plant growth runs short on an immobile nutrient, it can’t rob it from the lower leaves on the plant. The new growth just turns yellow and is short on that nutrient. These nutrients include Sulfur and the micronutrients. While N, P, and K seem to get all the attention, we are actually seeing quite a bit of Sulfur deficiency across the country. In many cases, applications of Sulfur are providing a tremendous return on investment. With the micronutrients, I rarely see a plant tissue test that doesn’t have at least one if not several micronutrients that are low or deficient in corn. Zinc is by far the most common, but Manganese, Boron, and others are short very often. The challenge with many of the nutrient deficiency symptoms that show up on the upper leaves is they are difficult to tell apart. Sending in a plant tissue sample is the best and most accurate way to see what exactly is going on in your field.
Identifying the visible nutrient deficiencies in corn is important so you can fix them for future years and break through yield and profit barriers. I encourage all farmers to use plant tissue analysis during the season to detect “hidden” deficiencies that are bad enough to hurt yield but not big enough to show visible symptoms. My brother Brian often compares the “hidden hunger” of unseen nutrient deficiencies with the way you feel before you get sick. Oftentimes, long before anyone else sees you’re sick, you know it’s coming. Plant tissue analysis is a cheap, easy, and effective way to see what nutrients your crop is lacking. Go to the Resources Page at www.agphd.com to learn more.