Dry Weather Thoughts

The best way to break the drought is to write an article from extension about dry weather. So, here’s a stab at trying to make it rain.

Today’s hybrids have amazed farmers on their yields in dry environments. I often get questions about early season drought stress and corn rolling in the early vegetation stages. I will talk in general terms about crop physiology and the impact this could have on yields.  We all have hybrids, fields and soil variability that can influence specific environments. Each year has challenges for maximum grain yield and this year is early season moisture stress. 

So, let’s do some cowboy math we need on average 20 inches of moisture to make a corn crop.  Well, where does that come from?  Yes, rainfall and soil moisture. The soil moisture component is related to the soil type and water holding capacity. Most all Iowa soils do a good job of holding between 8 to 12” of plant available moisture (yes, a wide range).  So, we need another 12 to 8 inches of rain during the growing season (April to September). Here we are in early June with a less than full soil profile in most of Southwest Iowa and other portions of Iowa. 

Let’s get back to the math. Drought stress on early vegetative stages of corn does a few things including reduced internode elongation and leaf expansion, which results in shorter plants with less leaf area. The estimated yield loss from this is a TRUE guess, but some estimates are approximately 1 to 2% per day with leaf rolling in early vegetative stages. Most corn is now transitioning to the mid vegetive stages, V6 to V8, and drought stress during this stage can result in fewer kernel rows, where later vegetive stages (V8 to V17) may cause less kernels per row. Later vegetive stage yield loss estimates are more like 2 to 3% per day with drought stress.  

Now what happens when we reach reproductive development?  Things get serious rapidly.  From pollination to R2, drought stress yield loss adds up to 3 to 9% per day and does not slow down until we reach the dent stage (R5).  In drought stress conditions after pollination, kernel abortion occurs at the tip of the ear. Typically, this happens during the first 14 days post pollination. When drought persists into the kernel filling stages, yield loss results from decreased kernel weight and premature maturity. 

Now, hybrids today are much better than previous hybrids, like those from the dry year of 2012.  Additionally, no one knows for sure what the next few months will look like from a moisture and temperature perspective. This article is not to push the drought scare button; however, it is meant to provide a roadmap of the impact of dry weather and corn physiology. I can speak for most of Southwest Iowa in the fact river and stream levels are extremely low for this time of year, and with the low subsoil moisture levels, we will need additional moisture in the future to help with our yield potential for 2023.  I hope this article makes it rain on your farm, and we can all get some needed precipitation.