▶ Wisconsin Soil Test Results Summary

0:05
Perfect.

0:07
So what I’ll be discussing today is a summary of soil tests that were aggravated or aggregated from DATCP certified soil testing labs and go ahead and advance the slide please.

0:25
So the the period we aggregated for was 2020 to 2024.

0:34
This four year reporting period covers a sampling interval for farms in a nutrient management plan.

0:39
So hopefully the summary is sampling many of the same fields at a similar intensity to previous plans.

0:50
So the information we requested from the labs and aggregated from our own lab included test results for bray phosphorus, bray potassium organic matter, pH, buffer pH, county information and sample date.

1:06
Go ahead and advance the slide please.

1:11
So we we averaged slack the data points statewide by county.

1:17
So we reviewed them against long term trends.

1:21
This year’s summary was composed of 1.8 million samples and so that’s an increase of about 200,000 samples from the previous four year summary period.

1:33
So of course with this type of sample summary, the results are not necessarily from the same locations as previous surveys, but hopefully the large numbers of data points can cover some of the sampling variability and let us tease out some longer trends.

1:52
Go ahead and advance.

1:54
So when when we look at the statewide averages, this table has data from the 2024 summary and the 2015 to 2019 summary.

2:06
The first row is pH, the mean.

2:09
Maybe it’s ticked down a tenth of the pH unit, but the median to means from the most recent survey and the previous survey all match. Phosphorus

2:20
We’re seeing a one point increase both for the mean and the median.

2:26
You’ll notice that the median and the the mean and the median are somewhat separated.

2:31
This is in effect that we see probably related to spatial variability sample to sample.

2:40
And so we have hot spots of phosphorus and landscape.

2:43
Some of those are things like vegetable production areas.

2:50
There’s probably some samples that are the old, old barnyards or places where the manure spreader got turned on close to the barn on a cold winter day that we can see in these values and that just general differences from field to field and how nutrients have been managed in the past.

3:11
When we look at some of the longer term trends, I’m not going to necessarily say that the phosphorus is going up just based on it’s 1 sample data point.

3:22
When we look at potassium, we do see about a a 4% increase in the mean value from year to year or from sample summary to sample summary.

3:34
There’s also this sort of difference between the median and the mean of the value used for the sample set.

3:40
Of course, we have the same sorts of nutrient management differences between different fields, different rotations and different histories and nutrient management throughout the state.

3:58
Organic matter is right on when you look at the state average, not not much of a change.

4:06
Of course, this is one of the more difficult soil test attributes to change one way or the other in an agronomic situation.

4:14
And so that that’s the sign that everything’s looking good.

4:19
In terms of how the data is. I’ll go ahead and advance slides.

4:24
So we’ll go over phosphorus, we’ll look at long term trends.

4:29
We’ll also look at some of the geographical distribution of phosphorus within the state.

4:37
Go ahead and advance to the next slide.

4:40
So we’ve got this history here of the mean value, the average value for soil test phosphorus in the state of Wisconsin.

4:53
So this this value starts in the mid to late 60s and we’ve got it gradually building till right around the year 2000 where it seems to plateau and then it’s gradually dipped.

5:12
So the different types or the different types of fertilizer management, we look at many states in the North Central region building soil test levels to encourage productivity was a big part of agriculture through the 70s and 80s.

5:30
And as we’ve reached these levels that are above the agronomic optimum, at least when we look at that the means we’ve started to pay more attention to split nutrient management aspects and are gradually drawing down the soil test levels of the state the I’ll go ahead and advance slide.

6:00
So when we look at the spatial distribution of phosphorus on on this, the scale for this map, we’ve got high phosphorus levels as very dark colors and low test levels is light colors.

6:18
So the range of county averages was between 60 and 143.

6:24
Higher soil test levels are more common in areas with lots of vegetable production.

6:30
You’ll see that in the Central Sands counties also in some of the northern counties. When we look at county by county breaks down, 58% of counties increased, 39% has decreased or had no change.

6:48
So this suggests that we may be having phosphorus ending up in certain parts of the state at higher levels as this map shows.

7:00
And next we’ll talk about potassium.

7:04
So advancing to the next slide, we can see some of the long term potassium trends.

7:12
We’ve got levels that have started out at low level, we’ve built up into more agronomic range.

7:22
And during the early 2000s, we either intentionally or unintentionally begin to draw down those levels.

7:31
And over the last cycle, it seems like we’re having a bit of a turn around where the soil test levels are starting to creep up again.

7:43
I think this is really good news for the agricultural productivity in the state.

7:46
Of course, with potassium, we don’t really have the same types of environmental concerns.

7:51
We would have phosphorus.

7:54
So the only possible downside I suppose would be that I have somewhat increased levels of chloride in certain areas since most of the potassium were applying that’s not coming from manure, it’s going to be applied to potash.

8:10
Go ahead and advance please.

8:13
So the next map shows potassium distribution.

8:16
Once again, the scale is from lighter colors or lower levels.

8:24
Darker colors or higher levels, potassium maybe will look a little different.

8:30
Our sandier soils tend to be less responsive to increases in potassium fertilizer leading to test increases in the same way we see in the coarser textured soils.

8:44
So we can see some of the sandy areas in the in the state looking at Adams County as I say this, but some other parts too that probably are are receiving potassium fertilizer tend to have some of the lower soil test levels.

9:03
When we look at finer textured soils throughout the southern part of the state, we’re seeing higher soil test levels and yeah, kind of mixed bag through the north.

9:14
So in general, 79% of these counties increased in soil test K, 15% of counties decreased.

9:28
All right.

9:29
So for pH, when we think about pH, it’s influenced in less direct ways then say the P&K levels, the inherent soil properties have a big role to play in certain parts of the state.

9:48
Look at the feel free to advance the slide, we can see this.

9:54
So we’ve got the blue colors are either extremely weakly acid or basic.

10:07
The dark blue of course we could see in the eastern part of the state where we have neutral to basic soils.

10:16
Then when we look at soil test levels through the southern part of the state, the test the summary test values are coming out in the close to ideal for some of our legume forages.

10:34
Other parts of the state, the averages are lower weekly acid or in some of the Northeast counties there’s a few that are more strongly acid on average.

10:54
Feel free to go ahead and advance the slide.

10:57
So looking at organic matter, go ahead advance.

11:03
We’ve got a number of different soil tests levels throughout the state.

11:08
Darker colors are more intense.

11:10
So we’ve got probably more recently drained swamps or higher organic matter soils in the north.

11:22
We’ve got molisols in the South where we have plenty of organic matter as well.

11:30
The general patterns we’re seeing of course or that sandy soils in many situations are tending to have lower organic matter levels.

11:43
Although the mix of soil types we have in some of our counties doesn’t always show this as clearly as what I expect.

11:55
Feel free to advance the slide.

11:57
So it looks like our long term P trend may have stabilized.

12:04
Potassium values are on the rise.

12:07
We don’t have any really apparent differences in pH or organic matter.

12:13
There’s more soil testing going on in the state and it’s probably a combination of more acres and probably higher sample intensity on some farms as well.

12:26
Although it doesn’t seem to have had a real apparent effect on the the trends we’ve been seeing.

12:36
I guess I have a few acknowledgments to make as well.

12:39
And so thank you to the DATCP Certified Labs for sharing the data.

12:45
This is if you look at something national soil test summaries data set we have here is much more complete.

12:52
Thank you to Hava Blair from Snap Plus for compiling the database, and thank you to Cody Calkins for during the statewide maps.

13:06
I guess if there’s any questions, I’d be happy to take them.

13:10
If you’re not able to ask them now or want to reach out on a similar topic, go ahead and send me an e-mail that e-mail address.