Rainfall last fall and this spring has filled our soil profile to the point most drainage tile is flowing. Normal use to this point in the growing season is about 5 inches. Our rich Northwest Iowa soils have a crop available water holding capacity of 10 to 12 inches in the top five feet of soil. This is currently at full capacity. A corn crop uses 20 to 22 inches, if it is not under any stress.
While there is a long way to go before harvest, the crop needs only 6 to 10 inches during the next 12 weeks to achieve full yield potential. The good early conditions will cause the corn to increase the total kernel count per ear better than last year.
While the soil profile is nearly full, it is not pouring out of our drainage system. This can cause a flushing of nitrogen past the corn roots into the waters that lead to the gulf, where it is a problem.
When the corn tassels here in four to five weeks, we will have used up about half the water needed to make the crop. If our tiles are still trickling, then we will have enough to make it until harvest. We are in much better shape in 2022 than in 2021, when we were surprised at the good yields.
One popular method of determining the water received versus the rain that falls, is called the checkbook method. You start with a balance – in our case of 12 inches – add rainfall each week and subtract the use, which is about 1.25 inches a week for the next 10 weeks. If the balance never goes negative, we should have a bumper harvest. If the balance goes over the 12 inches, then it runs off or out the tile lines and loses both water and fertilizer. Using a calendar is a fun way to keep track and see how well it predicts the stress and yields.