Soil Sampling - What we've learned

On the website, we've laid out a 12-step program for increasing the yields on your farm. Today, we'll focus on two of those steps that should be done in the fall, and talk about what we've learned where they've already been completed.

Our first topic is soil sampling. We'll cover what we learned this year about the cost of sampling, managing fields according to samples, grids versus zones, and fertility issues in drought areas.

Lesson number one that many farmers learned this year is that soil sampling can certainly pay, but to make it affordable, develop a plan to sample part of your farm each year. This makes the cost of the program very reasonable.

Lesson number two was that once you take good samples, you need to manage your fields accordingly. I'm not necessarily talking about variable rate spreading or GPS this or that. The system is only as complicated as you want to make it. For example, on one of our fields, we learned that we were short on two micronutrients, Boron and Copper. Not exactly high on anyone's priority lists normally, but in that particular field, next spring we will need to add some micronutrients to the starter fertilizer we put on with the planter. For one field, we'll have to do things a little different, but it should put more dollars in our pockets come fall.

Another example would be your soil's levels of P2 Phosphorus. Where levels are very high in the P2 category of Phosphorus, which is the total P in the soil both available and stored, you need to manage the field a little differently. Phosphorus can tie up other nutrients like Zn making them unavailable. Also, if your applied Phosphorus is simply getting tied up in the soil rather than becoming available for your crops, you will need to make a chemical change in your soil over the long term and band fertilizer each year to put Phosphorus where your plants can get it.

A change like that can not only save you a lot of money in fertilizer costs, since you won't need to broadcast P, but it will also make you more profit as your crop is allowed to access more Phosphorus each growing season. For a small investment of soil testing, even gaining a couple of bushels on your entire farm will MORE than pay for the cost of the tests.

One question we met head on this year on our farm was the cost difference between ZONE sampling and GRID sampling. We've all seen the colorful maps made by companies that provide grid sampling software and farmers who have adopted this system on their farms. There's a lot of information there, but unfortunately, many farmers either don't have the technological equipment capabilities or the desire to manage their farm down to a 1 or 2 acre level.

Besides that, there may not be a need for that kind of management every year. With zone management, similar activities can be done and comparable gains can be made, all for a lower price tag. Many top growers are managing their farms by the various zones of different soil types within their fields.

Establishing these zones is where grid sampling comes in. We really encourage you to use the latest technology to map the soil types or zones within your fields. Electroconductivity tests have now been nearly perfected by top soil sampling firms and crop consultants. The best thing about them is that once you map your field, you won't have to do it again for 20 years or more. Divide that cost out over 20 years and it's VERY reasonably priced.

Once you have the soil types mapped out, you can improve them zone to zone, instead of having to try to manage one or two acre blocks with varying soil types. In those zones, this year, we learned a few things about pH and nutrient deficiencies and about soybean cyst nematodes.

We have been aggressively using lime and gypsum, the two main soil amendments, to try to correct soil pH on our farm. When our first soil tests came back this fall, on some of them, even where Magnesium levels were very high, there was no gypsum recommendation. With most labs you send soil samples in to, you need to specifically ask for a gypsum recommendation in order to receive one. Gypsum is not as quick a fix as lime and is not as mainstream as well. However, we are currently working on measuring the results of gypsum in tests we're doing cooperatively with state university specialists. We'll share those results with you in the coming year.

We also have done a lot of work with lime. The optimum soil pH that we're targeting in a corn and soybean rotation is around 6.8. Our normal practice has been to recommend lime applications only where soil pH is below 6.3. We were really curious how the soil pH varied down through the profile, though, especially as we are trying to farm vertically encouraging deeper root penetration.

We did standard six-inch cores and sampled the upper topsoil. We also did tests down to 24 inches to see how conditions varied in a part of the profile we haven't addressed. In areas where our soil pH was below 6.3 in the top six inches, we found more acidic parent material down deep in the profile, which validates the need for lime applications. Conversely, where soil pH was above 6.3 in the top six inches, the pH deep in the profile was considerably higher as well and wouldn't need pH adjustment.

Earlier, we discussed a shortage of Boron and Copper on one field, but nutrient deficiencies were very common this season across the Upper Midwest. Rather than put blame on specific hybrids where deficiencies were seen this year, watch soil tests for zones within your fields that need additional primary, secondary, and micronutrients. If levels are exceptionally low, address concerns with your starter fertilizer and early foliar applications. Where levels are trending lower and may become a problem at a future date, broadcast applications can still be used, but keep in mind that the crop response is not nearly as quick as with foliar and starter applications.

And finally, one of the more destructive factors that showed up more than ever this season was soybean cyst nematode. We knew this problem was really spreading west fast and the numbers of SCN were growing in the fields the cysts are present in, but the results we've seen from yield data and soil tests have been shocking. If you haven't tested your fields for soybean cyst nematodes and you plant soybeans, get them tested. It's cheap, easy, and very important.

The seed companies are all gearing up and raising more nematode resistant beans each year. The yields of these varieties are really gaining on their susceptible counterparts. Some of the new nematode resistant beans are beating the non-resistant beans released just a couple of years ago.

To sum up the lessons we learned about soil testing this year, we learned that you can certainly justify the cost of in-depth soil analysis, especially if you divide that cost out over a four year plan. Grid sampling is nice, but zone sampling and management can be just as effective.

The most important things from soil tests this year were pH variability, nutrient deficiencies, and the increasing numbers of soybean cyst nematodes. Trying to make decisions on the farm without good soil tests is like a football team trying to call a play without knowing what down it is or where they're at on the field. There's no way to know where you'll get the best return on your dollars.