Soil Sampling – Consistency

Soil Sampling – Consistency

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Now, let’s get to it. So our last couple episodes, we’ve been talking a lot about consistency and how we gain those highest yields by getting the most consistent stands out in the field and what we can do at the planter to help us gain those consistent stands. Today, I want to kind of talk a little bit more about consistency, but I want to talk about it with a different activity on the farm, I want to talk about soil sampling. Soil sampling is a pretty important project this time of year. A lot of times we want to have that soil sampling done by about the first of December, in case we were to get any moisture and really freeze up that ground, it becomes difficult to do that soil sampling. So talking about soil sampling this time of year and talking about consistency. One of the questions I have, and I’ve talked to a lot of growers about this before, and they say, well, the results are just inconsistent. And my question is, why do you expect consistent results? I think the reason that most people expect consistent results from a soil test is they view soil as this inner matter. So we got sand, silt and clay, and then we got these nutrients, nitrogen, phosphorus, potassium, zinc, boron and so on. They view it as those results that they get from the test. And so why would that change? Why wouldn’t we see a consistent result from that? And the reason we don’t see consistent results from that is because soil is a living organism. A healthy soil has nearly 4000 pounds of microbial biomass in each acre, and those microbes, the functions of them, are constantly cycling nutrients between plant available forms and forms that are tied up in the soil; tied to another molecule or to one of those sand, silt or clay particles, and so because of that biological function of the soil, we’re not going to get consistent results every time, year after year, because you have different amounts of soil moisture, different soil temperatures, and those things affect the biological activity in your soil, as well as crop rotation, chemical use and lots of other things. 

I want to talk a little bit about, what is the goal of soil sampling? And so I’ve got a couple  different goals when I go to the field for soil sampling. One of them is I need to analyze what soil nutrients are in my soil and what’s potentially available to the next crop, so that I can make a budget decision on what fertilizer I’m going to use this year to produce that crop. Then, when I’ve done that, the other thing I want to focus on when I’m going to that field and soil sampling is, how do I apply consistency to my sampling procedures? Then when I do that, I look at the changes in available nutrition and available fertilizer to my crops over time. One of the things that I think is very important when you go to the field and you do soil sampling, in order to look at it more consistently, is you need to GPS locate the sampling points where you’re going to in the field. What I generally do, there’s a couple different apps out there that you can use, but take one of those apps, map your field, place the sampling locations on it before you go to the field. When you get into the field, then jump on the four wheeler. You can drive from location to location and pull those samples. The thing about that is, you’re not going to be able to pull a sample out of the same hole year after year, but you’re going to get in the same general location. In every location I go to, I always pull three cores. So one out in front of the four wheeler, and one at a 45 degree angle from the back side on both sides of the four wheeler, so you get those three cores. You mix those together, you go to the next location. You get three more cores. You mix those with the first three, go to the next location, and so on. 

By doing that, you get enough cores out of the field, enough random locations, you get a good, consistent analysis of that soil. The reason you need enough cores to get that good, consistent look is because, even within one foot of distance, the analysis of that soil is going to be different, and so you want to go out there, you want to make sure you get enough cores. 9 to 15 is recommended if you’re just taking a composite sample across the field. The same is true if you’re doing grid sampling or zone sampling, you need at least nine samples from each one of those grids or each one of those zones. When you’re doing that, that’s kind of how you use consistency in sampling. From a sample point perspective, use a GPS location every time you sample that field, return to the same location, get back into that app, get into that same field, and go and sample those same locations, so that you get a consistent look at that field over time. 

The second thing that you want to focus on, to have some consistency in your sampling is the timing in your rotation, or the time of year, or both. So if you have a real standard rotation, say, wheat, corn, fallow on your dry land, you want to always sample at the same point. And I like to sample after the wheat, before the corn, because the corn seems to be the most profitable, the most viable crop there of the three, and so sample after the wheat and before the corn, so that we make sure we have what we need to grow that top yielding corn. Then make sure we leave some residual fertility in that system for that wheat crop when it’s coming up. If you don’t really have a very good rotation, one of the things I do on my farm is I sample every year. I try to sample every year in November. So time of year has an effect on how those samples read out from a couple different perspectives. One, if you go in there at the time of year where you’ve just taken a crop off. So say, we’ve harvested this corn crop. We go in there, we take a look at the soil analysis. In November after corn harvest, then we get that consistency of having that sample after that crop. The other piece of it that creates some consistency is the time of year somewhat dictates the amount of biological activity that’s going on in that soil. From a soil temperature standpoint, these microbes, the warmer and wetter the soil gets, the more they work. So as we’re cooling off this time of year, into November, it’s a good opportunity to get those samples when that biological activity is at a similar level, year over year. Next piece you want to focus on using some consistency in, is the depth of your sample. So I always try to sample, six inches deep every time I go out. Then, if I’m pulling like a deep core for a soil nitrate analysis I’ll pull a 24 or 36. So 0 to 6 that goes into my composite, that’s the one I’m going to use for the total analysis of all the nutrients, NPK, calcium, magnesium, boron, zinc, sulfur, iron, etc. Then that deep one, we’re really just looking at soil nitrate availability, so 0 to 6 for the complete and then 6 to 24 or 6 to 36 for that soil nitrate. 

The next piece, I think that’s important about using consistency here is that you always use the same lab. Different labs have different methods of analysis, whether that’s the chemical that they use to extract the nutrients from that soil sample, or whether that’s the timing, the length of time that they put that soil in that chemical extract or how many times that it’s shaken after it’s combined with the extract. There’s different methods used by different labs, and so you want to use a lab consistently year after year, so that the analysis that you’re seeing has that consistency to it. Then, the final thing after we’ve done all these things consistently. We’ve got the consistent GPS locations, we’re using the same time of year, the same depth of the sample, we’re using the same lab, then we take those samples, we can make a better decision about the amount of nutrients needed for this crop and future crops in the rotation. Because we not only can look at this year’s sample, but we can look at the change in those soil nutrient availability year after year or over multiple years, when you’ve done this, say, for 10 years or so, and got that consistent long term look at the soil. So that’s how we’re going to apply consistency to this, this time of year, the soil sampling activity that we’re doing in the field. That’s all for today. I’m Matt Long. Thanks for joining us on this episode of EZ Ag. Grow your Yield. Grow your Legacy. Grow Strong with Axis Seed.