Ag Geek Speak
GK Technology Inc Team Members, Jodi Boe and Sarah Lovas talk about precision agriculture, agriculture mapping, agronomy and drainage.
Ag Geek Speak
15.5 Precision Composite Soil Sampling Explained
We unpack why “precision composite soil sampling” isn’t a contradiction and show how GPS-marked points turn an old method into a reliable trend tool. We cover workflows, gear, timing, and when shifting results should push you toward zones.
In this episode we discuss
• Pre‑GPS composite sampling and its limits
• Marking exact GPS points for repeatability
• Keeping post‑harvest or spring timing consistent
• Tracking year‑over‑year P, K and pH trends
• When composites signal a move to zones
• Benchmarks versus wider composite coverage
• Core counts for quarters and half sections
• Gear tips: external GPS pucks and apps
• Faster fieldwork once points are mapped
• Starting with GK Field Mapper and ADMS exports
More info about GK Field Mapper here: https://gktechinc.com/gk_field_mapper/
Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that!
https://gktechinc.com/
And now it's time for a Tiny Bite of knowledge. Jodi, we are going to talk about the biggest oxymoron on precision agriculture ever.
Jodi:Ooh, what's that? Using foam markers on a tractor with auto steer ?
Sarah:Close, but no banana. It is talking about composite soil sampling that's precision. Precision composite soil sampling. Have you ever heard of that idea before? I don't know. Have I? It sounds a little intimidating. Is what does it involve? Well, it involves a GPS for one. I think I can deal with that. Well, let's back up and talk about what a composite soil sampling is and what we used to do with soil sampling before we got into precision soil sampling. Did you ever soil sample before precision agriculture was around Jodi? And if so, how did you do it?
Jodi:No, because uh I think uh what is it, the first GPS installed inside of a tractor was like 2003. So I was a very young girl who was not soil sampling at that time. Gold, but dang. To answer your question, I have soil sampled before. Actually, you know what? I take that back. I have never soil sampled without marking my points exactly where I took a core. But I want to hear your perspective.
Sarah:Well, here is age before beauty and all that. Here we go. Let me explain to you how we used to do it in the old days when we used to walk three miles uphill to school and three miles uphill back home again, and we couldn't tell because we didn't have LiDAR to tell us where a uphill was. But anyway, back in the old days before we had GPS, the way that we would soil sample is you would pull into a field, let's say it's a quarter section, you know, 160 acres, for example, and what you were trying to do was get an average uh soil analysis value for all your soil sampling parameters. So you would soil sample, you would take approximately 20 to 25 cores in the field randomly through the field, but in areas that were quote unquote thought of as average. So you would stay out of your headlands, you would stay out of that low pothole, out of the ditches, those kinds of things. If you knew where an old farmyard had been where there had been a lot of manure or weird things going on, you would stay out of that spot and soil sample the the rest of the field without that rich area of manure. And that way you would get an average value. So when we start talking about composite soil sampling, it's kind of like the oldest fashioned way of doing soil sampling ever. You don't need a GPS, you just visually look across the field and you try to figure out where those average spots are and you go and pull them, take 20 to 25 cores in a quarter, you get them back, and you get that average soil test. That's how we did it in the old days.
Jodi:Sounds wonderful. But it sounds like there's a more precise way to do this. Yes.
Sarah:There are many people today where composite sampling maybe is still a fit, but there are more precise ways of doing composite soil sampling than the old days. You can go out with a GPS and find those spots on the field where you want to pull those cores from, those 20 to 25 cores, and you can designate where they should be pulled from either ahead of time or when you're in the field. You can mark them as you go. Some people might put those points on a map before they go out there. Then what you can do is soil sample every year in that same spot. So go back to that same point every year. And theoretically doing that at the same time of the year. Now, when I'm talking the same time of the year, I'm talking about like post-harvest or spring, but let's not do spring and post-harvest. Let's try to be consistent with the general time of the year when we're pulling those soil samples.
Jodi:That is that's such a great, great way to do it. Um, I mean, it sounds like, and and having worked at a soil testing laboratory, one thing that's really important about looking at soil test results is that it's really nice when you can compare from year to year, right? If you're asking the question, like, am I building soil test phosphorus over time? Um, am I, do I seem to reduce in phosphorus over time? Do I seem to reduce in potassium over time or maybe increase? If you're not pulling the cores in the same areas of your field from year to year, and when I say same areas, I mean from those same precise points that are marked, it's really hard to say whether or not that difference from year to year is because of a fertilizer practice, something that you've done or haven't done, or if it's just because you've you've put or drawn a core from someplace outside of where you did before. So adding, simply adding that precise, the precision component of sampling in the same place from year to year adds so much value in terms of what those total test results can tell you about a field.
Sarah:That's so true, Jodi. You know, there's places around here in the Red River Valley of North Dakota that are pretty flat and pretty consistent across the uh across the landscape. But uh, and and composite sampling actually works fairly well in some of those fields. And some of those fields you still need to think about doing um zone management, even when there is the same soil type in the same field and it's all flat. But if you use precision composite soil sampling where you soil sample in the same point every year, if you get a different value, for example, of your soil pH or your phosphorus from year to year, that can be a trigger to tell you that you should probably start thinking about adding in some other precision soil sampling concepts. It might be time to think about doing some zones, just trying to figure out if there's something different out there.
Jodi:That's such a great point, Sarah. So, another thing to think about too is there's a form of soil sampling or a more precision coded version of composite sampling where you set benchmarks out in a field where you measure the same area, you choose where your benchmark is going to be, and then you sample that same spot from year after year after year. The one challenge with this is like, even though you might have benchmark spots that you decide that represent the whole field and you're going back to that same spot year after year, the challenge in that is that it's hard to pick one spot or even like three spots that really represent what, like, how do you choose one benchmark spot that you're coming back to every year that represents the whole field? So it's another way to do it. But if you ask, I mean, if you're gonna be the person that picks the benchmark, and anybody that doesn't know the field isn't gonna be what the one that wants to choose that, by doing more cores across a wider area, like you would in composite sampling, right? Like you recommend 15 to 20 cores in every zone or every, I don't know. What is your how many cores do you like in your composite sample, Sarah?
Sarah:For a for quarter section, I usually like to pull 20 to 25. If it's a half section, I'm up at like 30 is usually pretty standard, 30 to 35, something like that.
Jodi:Yeah. So just, I mean, spreading out that the spatial variability, even though you're only getting, you know, one result with a composite or a benchmark with that composite where you've got those 30 different soil sampling points that are coming together for the average, you're really spreading out that variability and getting a more average rate or an average soil test result. So just something to think about when you're considering these things. But yeah, I mean, if if you're somebody that's soil sampling and you know, you're doing composites and you just want to level up the value of what those soil tests are coming back as and what they're helping you or your customers do in terms of soil fertility, get out there and get a GPS. Yes, most phones and a lot of tablets will have an internal GPS, but if you get like an external GPS puck, like a Garmin Glow or others that you can connect to your devices, those tend to be more reliable. And you can go ahead and start marking those solo sample core points so that you can come back to those every single year. And not only do you get the benefit of hopefully stabilizing those soil test values over year or year over year, so you can do some comparing and contrasting, but also it can hypothetically speed up the time that you're in the field. If you know where your points are going to be, instead of having to decide in the field where you're gonna sample, it can speed up your soil sampling process too.
Sarah:Actually, Jody, I think that's a very important point for this particular podcast. Once I started marking points in the field, um, the first time I would lay out my sample points, um I would create those points when I was in the field and I wanted them to be well, you know, good, good points that I was laying down. And so the first time that I would lay those soil sample points out, it would take me a little bit longer. But then the years that came after that, boy, it sure sped me up. I knew exactly where I was supposed to be going. And, you know, up here in the northern plains and North Dakota, it actually gets dark, you know, pretty early in November. And so it actually has helped me work a little bit longer into the night, like, you know, eight o'clock at night, nine o'clock at night, if I needed to get something done before we had some weather coming or whatever, and it was getting dark outside. So it's always nice when you've got that computer there and you know where you're supposed to be driving.
Jodi:Absolutely. So speaking of like advances in technology over time and moving from, you know, non-precision composite sampling to precision composite sampling. And if you're somebody that's been sample soil sampling for a while and you want to not have a computer in your vehicle, or if you're if you're looking to start collecting these points where you're pulling samples from and you're doing composites and you've never done that before, really, really great place to start is to download the GK Field Mapper app. Um, just the free version. You can record your soil sampling points, you can keep them in your phone, you can save those soil sampling points for future use and you can come back to them year after year. And if you're somebody that's already has your points marked in ADMS, you can get GK Field Mapper where you can just export those points that you've got in ADMS saved right onto your phone, onto your iPad, your your Android tablet, whatever you've got, and have those ready to go and be out there making precise composite samples.
Sarah:You can embrace the oxymoron of precision composite soil sampling.
Jodi:Oh, I love that. So do I. Because at GK Technology, we have a map and an app for that. Tune in next time for a tiny bite of knowledge from GK Technology, where we have a map and an app for that.