Dr. Victor L. Martin
Unlike the wheat crop where there were a few pleasant surprises, this year’s corn crop has been pretty much as expected and maybe a little worse for some, even under irrigation. Let’s take a little time to explore what happened.
Dryland yields are pretty much what we expected, nonexistent. High temperatures, little to no rain, and wind combined with very little soil profile moisture resulting in the majority of the dryland corn in the area not being harvested for grain. It probably wouldn’t have made a huge difference but the cooler weather at planting and in May combined with corn going in later than usual added to the problem. When it is this dry, even no-till planting isn’t of much use. This summer is a good demonstration of Liebig’s Law of the Minimum which states that yield is proportional to the amount of the most limiting nutrient, whichever nutrient it may be. In English, whatever factor needed for crop growth is in the least supply will determine crop growth and yield. Even though a producer supplied the proper nutrients, controlled weeds, etc. the lack of water was the yield (or lack of yield) determining factor.
Irrigated yields weren’t a surprise to producers although they had hoped for more. Several factors contributed to yields appearing to range from under 100 bushels per acre to around 150 bushels per acre with few bright spots. So what happened?
· Irrigated corn on sandy soils suffered more than on loamy soils since sands can’t hold as much water and water evaporates more easily from coarser textured soils.
· Low capacity wells simply couldn’t apply water fast enough. When the PET (Potential EvapoTranspiration) rate is close to 0.5 inches per day, a low capacity well can’t keep up.
· Just too hot. When temperatures are close to or over 100° F, plants can’t move enough water from the soil to the roots and finally the leaves to maintain turgor pressure so they wilt which is actually a protective measure for the plant.
· Wind. You don’t need a lot of wind when it’s this hot and many days were more than a little windy so the result is a plant that can’t move water fast enough further stressed.
· Low humidities. Water moves through the plant in response to gradients such as the difference between the water vapor content of the air vs. the humidity of the plant leaf environment. The movement of water out of the plant toward the area of lower water concentration (the air) drives water movement though the xylem tissue from roots to leaves. When the gradient is too steep, the plant shuts down to protect itself.
· Corn develops vegetatively and reproductively by accumulating heat. Flowering through physiological maturity of the grain takes a certain amount of heat. That accumulation was quite rapid resulting in a compressed grain fill period; less time for the grain to accumulate dry matter.
· Finally, corn pollination prefers relatively cool nights, much cooler than we experienced this summer. This meant that corn experienced poor pollination in many fields that resulted in poor ear fill.
Even all the water in the world can’t overcome that many obstacles.