(upbeat music)
-: This is Aaron Nygren with Nebraska Extension.
Wanted to talk a little bit about soil water use
considerations with cover crops.
So the stored soil water, that's often just been one
of the costs that we've associated with cover crops.
You know, it's a plant, it's gonna use some water.
We've been doing some research that says
that maybe that isn't as big of a cost,
especially when we look at an irrigated system.
So with Nebraska being the leading nation
or leading state in the nation for irrigation,
that's something we really need to focus on
in our soybean irrigated system.
So one reason for this is that it's pretty easy
to leave those fields fairly wet
at the end of the season.
We talk about trying to dry them down,
but it's just a challenge
with irrigation management
to really get that soil dried down.
So we store a little bit of extra water there.
One of the side effects of that is that we leave
very little room for off season precipitation.
And then at the same time with that,
we get a lot of runoff and we also get some deep percolation
of water through the system.
Now, if we looked at a dry land system,
that would be a different story.
So that with this talk, we really wanna focus more
on the irrigated system.
So dry land fields we typically will dry those down
quite a bit more
especially even down to a six foot depth,
which we're not gonna do very often
with an irrigated system.
So when we talk about soil water,
we have to really think about how that moves
through the soil.
So it seems common sense to say
that water recharges from the top to the bottom.
But you know, we don't always think of that.
So if we look at the top foot, if we have that top foot
above field capacity,
we're gonna start moving some water that excess water
above field capacity is gonna leach
down to the second foot.
You know, it just gonna move down over time.
So if we have these feet, top two feet above field capacity,
we can move quite a bit of water.
So the range is anywhere from 0.09 to 10 plus inches
of water per day, that can actually deep percolate
and drain through that soil.
So that's a considerable amount.
Now, if we think about a typical soil,
eventually we might have something that's maybe
at field capacity.
So in this case, our third foot is at field capacity.
That's still gonna move some water,
but maybe that's down about 900 of an inch per day.
So that helps us out a lot.
Ideally though what we would have as somewhere
we would have a dryer layer.
So if we have something at 50% of available water,
that really slows down our deep percolation
down to an inch or less per year.
So think about trying to manage your soils
in ways that gives you some dried layer
in there to help reduce that percolation.
At the same time,
if we think about one that's completely filled up
or you're the guy that cusses a rain
because, you know, he'd kept it so wet
with irrigation that it's just running off the field.
If we have that completely wet all the way down
that water is just gonna keep moving down.
So here we have all four feet above field capacity.
We're gonna deep percolate a lot of water.
The downside of deep percolating
all that water is any nutrients that are mobile
like nitrogen or sulfur,
are also gonna move with that soil water as well.
So that's what we wanna avoid in Nebraska
because we do have some issues with high nitrates and areas.
So this is something with irrigation management
if we could cut down on moving that much water
through the soil
that would really help us out.
So this is our recommendation.
We always recommend at the end of the season
to try to dry down an irrigated field
to 40% available water.
We feel safe with that,
that dragging it down to that level
isn't gonna hurt your yield.
And that would give us as much utilization
of that water that we have
in the profile to finish that crop out
also which would help our economics by reducing pumping.
So if we would reach this target, which I said is hard to do
we would have some pretty good storage left
in that field.
So on a sand we'd have about 2.4 inches
that we could store a loam 4.8,
or a silty clay Loam of 4.3.
Dry land field again, remember is gonna be vast
drastically different than this.
So we may have dried that down
you know, a lot farther all the way down to six foot.
So we would have considerable more storage there.
So looking at these amounts, if we look at what kind
of rainfall we get, it's definitely a challenge, okay?
So we would have room, you know, up to 5.5 inches
even on silt loams.
We just don't usually get it that dry.
So if we only have two or three inches of
off-season to store off-season precipitation,
what's gonna happen with all that excess water.
So in a minute here
we'll look at how much off-season precipitation we get
and keep in the back
of your mind that we only have maybe room for two
or three inches of that in a lot of irrigated fields.
So here we have the site that we're out here at Shelby.
If we look at that monthly total precipitation,
you know on the average for the season where the entire year
we're about 28 inches a little over.
But the main months that we wanna focus on
is the off-season pre sip.
So October through May.
You may say, why May?
We plant our crop in May, right?
Well, remember that crop is pretty small.
We're not using a lot of water,
so we still get more rainfall
than we have the crop actually use.
So if we look at that, we have a total here
of about 14.75 inches of water
coming in the off-season.
Now, if we only have room for two or three inches
you can quickly see where we have some runoff
or we have some deep percolation happening
on some of these irrigated fields.
So the four sites that we have this year are fairly similar.
So Arlington is around 15 inches
and then off-season 14 and a quarter
or 14 and three quarter in the Shelby area
like I mentioned.
Elgin around 14.25, and then 13 inches in the Hildreth area.
This is only looking through October through May.
And a lot of situations we could also include
at least probably half of June rainfall as well
because we still have a fairly small crop.
June is typically our highest rainfall month in Nebraska.
So we may have excess precipitation
that's gonna also help refill that soil profile.
Now we know that not all of that's gonna run in,
you know some is gonna run off,
some is gonna evaporate naturally.
So we can't count on all of that.
But even if we think about capturing half of that,
at six and a half to seven
half inches of water, so we could easily deep percolate
two or three or more inches on multiple fields
across the area.
So the take home points on this talk,
remember that any water that is deep percolated
is gonna move nitrates
and other nutrients deeper into the soil profile
which is something we wanna avoid in Nebraska,
with some of the high nitrate areas
that we have across the state.
At the same time
it may be advantageous to have
that cover crop using the water from the profile instead.
It's not only gonna help us out
with our deep percollation
but we also gonna get some soil health benefits as well.
And the water that we used by the cover crop
is likely to be replenished by rainfall
during the month of May and early June,
since that's typically when
we have the highest rainfall amounts
and the crop water use is fairly low
in those months as well.
So the next video we'll focus on planning considerations
with cover crops and irrigated soybeans.