Macronutrients and Drought

Perhaps a bit often over used cliché is that every growing season is different. True, but it always begs the question …. what is it going to be like this year? 2023 has certainly got off to an interesting start and let’s hope it finishes a bit less exciting.

The widespread drought across much of the Dairyland Seed footprint has given us some challenges in many aspects of crop growth and development. Nutrient sufficiency is not excluded. Extreme dry weather has a direct impact on the availability of many of those critical components. This week, we look at macronutrients which are nutrients required in large quantities by the plant. Let’s just say its gotten a bit colorful in the few weeks -- especially with corn. We have about every shade of green and not green in fields.

We are seeing a good deep green to purple to yellow. The yellow and striped corn we are observing this spring could have several causes.

The first possibility and perhaps everyone’s knee jerk reaction is nitrogen (N) deficiency. Deficiency does not mean there is not enough nitrogen applied, it may just be out of “reach” of the young roots at this time. Most of the yellow and striped corn we have dealt with is on lighter textured soils or side dress corn. Nitrogen moves in mass flow ….. with water. If no water is moving through the plant, then there isn’t much nitrogen getting delivered to said plant.
The other scenario is where side dress application was applied; however, there has not been sufficient moisture to get the nitrogen in soil solution and available to the plant. Compound that with limited precipitation, which is further limiting the root’s growth.

Another reason for yellow-striped corn, especially on lighter soils, can be sulfur deficiency. Sulfur (S) is mobile in the soil, like nitrogen. Mostly considered a secondary nutrient, it merits discussion. The cool weather restricting root growth in late April/early May kept the plants from accessing what sulfur was available. Now, we are facing limited water and both conditions combined contribute to restricted sulfur uptake. These conditions also limit the mineralization of S in the soil. In most situations, more ideal growing conditions should alleviate the symptoms. Yet in some areas, the addition of sulfur may be warranted. If this is the case, a standard practice is about 20 pounds of S.

As fair season picks up this summer, we all want that champion purple ribbon. However, purple corn is not desirable. We should be working our way out of this situation, but we are still seeing purple corn in limited areas. Since this article is more focused on the nutrients, we will focus on that aspect of purple corn. Phosphorus (P) deficiency is mostly a temporary situation in early season favored by restricted root growth. These root issues can be caused by soil compaction, side wall compaction, too wet soils and (see a pattern here?) too dry soils. Phosphorus moves to the plant through diffusion, moving from areas of higher concentration to those of lower concentration.

Last, but certainly not least, is potassium (K). This macronutrient can show deficiency issues in dry conditions as well since it moves through and to the plant via mass flow and diffusion. Yet again, water influences the availability of these important crop nutrients. Yellowing of the leaf margins that progress toward the center of the leaf is a common symptom of potassium deficiency. Leaf margins may turn brown and necrotic. Usually, older leaves or leaves toward the bottom of the plant will exhibit symptoms first, but whole plants can show symptoms during periods of rapid growth. Potassium deficiency can be found where compaction, ponding or root damage are prevalent.

In all the above cases, verify true deficiencies with soil and tissue sampling. This year it is more likely a transportation issue versus a supply issue. We have sufficient nutrients in the soil. It just can’t get to the plant.

Additional online resources for more information can be found at https://crops.extension.iastate.edu/files/article/nutrientdeficiency.pdf