Ohio Ag Net | Ohio's Country Journal Ohio Ag Net | Ohio's Country Journal 
By Vinayak Shedekar, The Ohio State University
If you practice controlled drainage during the growing season, do you think that controlled drainage helped your crop yields in 2023? It may be too early to answer this question, as many of you are still waiting to finish harvest. But if you are wondering about the role that controlled drainage played this year, I will give you a few tips on how to answer this question.
Monthly rainfall during the 2023 growing season
The early season drought affected crops across most of the state. If you can obtain monthly rainfall totals from an on-site rain gauge or a nearby weather station, look at the rainfall totals from April through September and compare them with average crop water use. The OSU weather station network website (weather.cfaes.osu.edu) provides weather data and graphs that can be helpful. For example, the Northwest branch research station in Wood County recorded lower than average rainfall during April, May and June, and slightly above average rainfall in July and August. Looking at the crop water demand in Wood County, corn experienced a water deficit of about 2.5 inches during May and June, and about 6 inches during July and August. Grain crops typically experience a 5- to 6-inch deficit in the months of July and August, and that was the case in 2023 despite above average rainfall in those months. However, unlike an average year, the corn crop likely also faced a water deficit of at least 2 inches during the early growth stages.
How much water can controlled drainage conserve?
Although it would be very difficult to generalize this, typically you would raise the water table in the control structure after field operations in spring (mid-June) to about 24 inches below ground surface elevation in the lowest spot of the field (typically, this is the farmable ground surface above the tile main just before it exits the field). Producers with more experience tend to set the boards closer to 18 inches below the surface. Be ready to actively manage that structure if you prefer to maximize storage by maintaining shallower water table depths. Considering that there may be 30 to 45 inches of soil water storage behind the control structure, how much water do you think is available to crops that would otherwise be lost through the tile outlet? The soil at that depth can retain about 0.5 to 1 inch of gravitational water per foot of soil, depending upon the soil’s texture and bulk density. A conservative estimate is about 0.5 to 0.75 inch of water retention, with an ability to replenish that storage every time there is a substantial rainfall event. During peak water demand periods, even though the corn roots may not have grown to the 24-inch depth, capillarity helps bring water from deeper soil layers to the roots. However, corn can use up to 0.3 inch of water per day during these peak demand periods. Thus, with controlled drainage and no rain, there can be about 2 to 5 days of moisture reserve in a controlled drainage system depending upon temperature and rainfall patterns. An additional 5-day buffer period may make a difference in crop yields, especially in a relatively dry year like 2023.
How to detect the effect of controlled drainage on crop yield?
An easy way is to compare the average yield from the field under controlled drainage with another field with a free-draining outlet. However, it may or may not be a fair comparison given the differences in soils, inputs, and other factors between these fields. A better option would be to look at your yield map and see if you notice greater yields closer to the control structure. If you want to get really accurate, get a contour map of the field, then draw out the area of the field that is within 45 inches of vertical elevation from the ground surface above the tile main near the outlet. Now this area is what you can consider to be the “zone of influence” for controlled drainage. You can divide up the yield map between the zones and compare the average yields. You may or may not see huge gains in crop yield every year, but in relatively dry years, controlled drainage can certainly help. The benefits to water quality as well as crop yields is what makes controlled drainage a win-win practice. Feel free to reach out to us if you have more questions or find something interesting.
This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, International Program for Water Management in Agriculture, Ohio Agricultural Research and Development Center, and the College of Food, Agricultural, and Environmental Sciences. Dr. Vinayak Shedekar is the Assistant Professor of Agricultural Water Management and director of the Overholt Drainage Research and Education Program in the OSU Department of Food, Agricultural and Biological Engineering and can be reached at shedekar.1@osu.edu.
