Dry June causes topsoil moisture concerns in southern, central Minnesota

So far this summer has been drier than average. On Thursday, the U.S. Drought Monitor released a map showing a large swath of central and southern Minnesota abnormally dry, with some areas moving into moderate drought.

University of Minnesota Extension professor David Nicolai joined MPR News host Cathy Wurzer to talk about what these dry conditions mean for farmers.

The following is a transcript of the conversation, edited for clarity. Listen to the full conversation using the audio player above.

Getting a little crispy in parts of Minnesota, where are the areas of concern?

Well primarily eastern Minnesota has been an area of concern. I would say in some of the areas in central Minnesota, there have been some occasional areas in western Minnesota. Most recently, however, we were able to come out of a little bit of that drought in terms of stress with some of these recent rains right along the I-90 corridor.

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So the bottom line, it's variable. When you look across the state, from east to west, and also somewhat to the west and the north.

You mentioned those significant rainfalls around the I-90 corridor, but like more than an inch, how much does that help?

Well, it generally helps quite a bit. If the rain doesn't actually run off the landscape, it has an opportunity for time to soak in. So when you have those really heavy thunderstorms, there are some risks that you won't get a benefit from that rain, however, things come a little bit slower, more like these garden variety showers of this morning, that will definitely help.

But we had a lot of variability. For example, I know that the Albert Lee area had quite a bit of almost flash flooding and rain. And you didn't have to go too far away — to the Waseca area — and it was under an inch. So again, a lot of variability with these systems where they're moving in.

How does this year compare to last year when we had that major drought across the state?

In terms of the drought effect, that we're not quite as severe if you look across the state of Minnesota. Generally crop conditions are still okay. If I had to give them a grade, I'd give them a grade of probably “B.” Maybe there's some crops that deserve a grade of “C.” Very few that I'd probably put into the “A” range. But certainly, we're in a much better situation compared to last year. We just really had an abnormally high temperature range here in the past 30 days in the month of June and that really aggravated things.

Evidently, the USDA says that about 75 to 80 percent of Minnesota still has adequate- to some-surplus stored soil moisture for the crops. It sounds like good news.

Yes, we really looked at two things. One is subsoil moisture, and one is topsoil moisture. And if we looked at our subsoil moisture, say, for example, this past week 73 percent, and the latest crop report was indicated as adequate. If we went to last year, only 26 percent was rated as adequate. I think that tells the tale in terms of subsoil moisture.

Recently, when we have these stresses in the month of June, really what we're talking about is more of the topsoil.

How long does it take for that subsoil to get sucked up and really dry out?

Quite a bit of time. There are really two things that happen here: we have evaporation off of the surface and transpiration out of the plants. Evaporation, you know, that will occur obviously, even in a wet situation here when the crop is smaller, and we can get evaporation. So that's a phenomenon early in the season for water loss.

And then the crop gets larger — particularly corn crop from that tasseling stage and setting a cob and so forth — that's going to be transpiration, where the crop is canopied over, and that's where we can get significant water loss.

So we're still not out of the woods, so to speak, in terms of that situation. We're OK now at this point. If we can keep up with regular rains and situations, we’ll still be adequate. But I think really, the tale will be what's the weather going to be like at the end of the month of July and early August?

What are you hearing from farmers?

I think the concern probably, to some extent, is elevated temperatures. If you have really intense storm situations that developed because of weather fronts coming in a little bit more than we've had in the past, you have phenomenon so high wind speed that can, you know, actually damage the crop in intense thunderstorms, or just too much rain in one spot.

So that frequency, I think that is of concern with farmers, you know, in looking at from the standpoint of a climate change and how that affects. Although these things happen more slowly. They're intense, but if you are in an area, you know, you're affected.