It always has struck me as a bit odd that we treat our soybeans so poorly. Many people act as if they are a throwaway crop. One that exists only to bridge a gap between years when they can plant corn. And I guess I understand it to an extent. If you work up break evens for both Corn and Soybeans, the Corn often looks better. But I don’t think that is the real reason. I think in a way, we tend to mock or ignore the things we don’t understand, and I will argue that for many of us, Soybeans is at the top of the list of things we really don’t understand.
Now those of you that have been following along with my blog this summer probably already know I am going to turn this into a discussion about irrigation. And you are right. But let’s take the long way around on our trip there.
Beans are a bit like a 2 year old. They are finicky, they like to be warm and dry, and they will fall on the floor and throw a tantrum if they don’t like what you are doing. So I think we need to approach this a little more like we are dealing with a 2 year old. You have to play mind games with them sometimes. Earlier in the irrigation season, we talked about managing the stress around them and forcing them to be uncomfortable to root down. One of the old Sage’s of the retail agronomy world put it to me like this almost 20 years ago; “You gotta stress them if you want them to yield.” Another one of my early mentors told me, “When it comes to beans, they need to die at least 3 times if you want to have a crop.” As weird as it sounds, those sayings have guided the core of how I have managed beans for a good many years.
But, (and there is always a but) there comes a day when that mentality needs to switch. Somewhere around the first of August, our beans change. Stress is no longer a factor that works in our favor to limit vegetative growth or promote rooting, but stress becomes a yield robber much like it is in Corn. And here is the simple fact, Soybeans can take being treated poorly in many aspects in June and July, but in August and September we have to act like we are growing corn if we want to have successful yields.
So then, here are the nuts and bolts of irrigating your Soybeans. If you look at the last 30 days of a Soybeans life, or roughly Beginning Seed Fill (R5) to Maturity (R7), we only cover 2 growth stages in that time, but the crop will need roughly 6.5” of water to fill out the seed. Yes, you heard me correctly, in the next roughly 30 days depending on where you are, your Soybeans are going to need 6.5” of water, or roughly an average of 1.50” per week. And while that is about the same amount of water that your corn uses in its last 30 days, the way they use that water is very dissimilar. Corn will slowly use less and less water, until it is down to almost nothing in its last week. Soybeans on the other hand are still pretty thirsty even after they get a yellow tint to the field. It really comes down to that last 1.5”-2.0” of water for your soybeans. Inside of those last couple of inches are several bushel. And I know that sometimes our rush to end the irrigation season kills those bushels.
This is where the probes come back into play. If total water was all we needed to manage to finish this crop it would be pretty strait forward. But we have some other issues at play, like white mold and lodging that are tied to our water. We still need to be vigilant about not keeping our soil surface or canopy any wetter than we have to. Letting that 4” and 8” moisture line drop before we irrigate is far better than giving it 1” every Monday. And frankly, this is where the ACS team, and your FSA want to help you. Ask us about water use rates, soil moisture status, rooting depth, and compaction zones. We have gone through far too much so far this season to leave any potential behind now.