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Jim Meade / Iowa City
Senior Advisor

Re: Grid sampling

To begin with, I don't think of each sample point as the center of a block of land.  We all know that samples taken even 20 feet away can be quite different.  We're just hoping for something representative.  So, in my mind, I see a field with a bunch of points on it, like measles.  In my case, the points are equidistant from other points.  I call this grid sampling only because the points are laid out in a square or other regular pattern starting along a fence line or some such.

 

Now, in my mind, I connect points based on similiarity.  I don't think of it as a block of color with a point in it.  I think of it as a point that I can connect to another very similar point.  At the end of the connections, I should have a line that follows a line of similar soil characteristics.  This might be along a contour line, it might be up a draw, it might be around a sand point, it could be straight across the field.  Some of the lines might seem to enclose a part of the field that I'd treat a certain way.

 

To me, the deal is to connect the dots after the samples are taken based on what the samples day, rather than take samples based on some idea that the contour is important or the yield map is god or any other preconceived notion.

 

If a person used the sample points a the center of a block and put tht in the variable rate applicator, platner or whaterever, it would end up the same as a zone map, anyway.

 

I just think that starting out with the assumption of a zone makes the soil sample process subjective rather than objective.

 

 

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Shaggy98
Senior Advisor

Re: Grid sampling

Sounds like your theory is similar to mine. The original grid or zone is only a starting point. After samples are patterned on a map the original pattern can be manipulated to create a pattern that will become more productive. Could it be that many of today's zone maps started out as grid maps and the information gathered after they were in place turned them into zones?
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Jim Meade / Iowa City
Senior Advisor

Re: Grid sampling

I agree with you.  But, recently a guy tried to convince me to do zone comverage without a good basis for defiing the zones.   That is whay I'm kind of firm about how one generates the zone.  Your way is a good one, and, as you say, it should be subject to change and refinement as appropriate.

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Shaggy98
Senior Advisor

Re: Grid sampling

Thanks for the discussion this morning, made that last 1/2 pot of coffee go that much faster.
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ECIN
Senior Advisor

Re: Grid sampling

Ok Jim - heres a couple of my farms  that are Zone tested

 

my documtims 627.jpgmy documtims 628.jpg

 

After readding how you connect the dots - would that be like zone - so to speak - Like the Shagster said - it's just a good starting point - theway most do a grid around here is just drive and pull one - then there is no defined are- other than its in a 2,5 grid - which we don't have a clue how they pulled it . the zone will define or give you a good idea of your area of type dirt . With the 2.5 you could half in two types of irt or maybe just a foot in that type - then that would throw of your reading some .

It has been interesting in how the samples come out - as to the type of dirt - the good dirt may not need as much as you woul think , because of Organic matter being better .

 

This sample was pull 2 fall's ago with the new ones pull this coming fall

 

I have tried to post up the prescription maps - but this dam computer of mine is showing a error , will try later

 

 

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idalivered
Advisor

Re: Grid sampling

I actually like the theory of grid sampling, but the reallity is that i just end up with as many questions as answers. One of my farm managers said that they hope to correct soil deficiencies by grids, but after 5 years of grid spreading, they get very similar results. My guy , did a grid sampling experiment. He and his 2 assistants all pulled cores in a 2.5 gridded field. they tried to stay within a foot or 2 of each "point". they came up with some very different recommendations in "almost" the same sample point. One of the three is correct. What I am seeing with the zone sampling is that the best soil types (nicollet in my case) was also the most depleted. Our assumption is that while it is the best csr we also have been removing the best crops from that soil type and consequently, depleting the p&k levels there also. There is probably holes in that theory and I almost feel better about blanket analysis spreading by sections of each field. All I can say is soil science is not an exact mathematical equation.

 

We did have 2 fields of lime spread last fall, variable rating by soil types. Makes the most sense for this application. imho

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SpringBrookFarm
Veteran Contributor

Re: Grid sampling

You can accuratly define zones with electromagnetic sled that reads the soil, kind of like a veris machine. being used alot now for variable rate irrigation.

 

I Do not feel grid sampling is dead is some respects. In some areas a zone may be 30 acres, are you suggesting the fertility in that 30 acres is comparable just because its the same zone? I dont think so

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SpringBrookFarm
Veteran Contributor

Re: Grid sampling

When it comes to soil sampling, i honestly dont think it makes a whole lot of difference. The only better way to do it would be to go to smaller grids, say 1 acre instead of 2.5. 

 

Here is my reasoning. All the data pulled in from gird sampled is interpolated and averaged to determine all the values inbetween the points of where the soil was collected. To many people just see dots in a field. Since we cannot collect soil from the entire field mathmatics and statistics have to come into play to determine what is in between all those dots. Whether you do your soil sampling in zones or grids really doesn't matter because the computer doesn't care. All it wants to do is gather the information so it can spit something out for every inch of the field. Having a grid sampled field with fairly evenly spaced points gives you a good overall sample of the field in question. 

 

Question. If you go to zones and say end up with a 30 acre zone are you going to only do one composite sample for that 30 acres? Do you really feel that just because the soil type is the same that the fertility would be? Wouldnt that be taking a step backwards, thats what we used to do in full field sampling. Even if i did zones any zone bigger than 3 acres would be grid sampled so i could get the most amount of samples. When it comes to soil fertility, the amount of samples you take the better it is. Kinda like when we did composits for entire fields, 20 pulls put together was better than 8, well zone and grid sampling is the same thing. Instead of us mixing all the soil together to get an average for the field, a computer is taking all those samples and tying them together to get an Approximate estimate of what is in between those points.

 

Now when sampling you want to avoid low spots or dips or terraces and terrace channels and that type of thing because that could scue the data, but outside of that im really not sure it matters, again if your worried about the accuracy of the test, i think doubling the amount of tests, like going to one acre grids would be better then simplly doing the same amount points just placed differently in zones rather then grids.

 

I dont know, i could be wrong. Soil sampling is important thing to do in our business and shouldnt be taken lightly, but at the same time i also feel people put way to much stock in it because the soil is a living organism in its own right.

 

I do know that i love the information i get from grid sampling compared to what we used to do.

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Jim Meade / Iowa City
Senior Advisor

Re: Grid sampling

Based on the messages and thoughts expressed, maybe it would be good to define what we mean by grid and zone and for that matter point sampling.  As was noted, soil samples a foot apart can be consistently different.  What does that mean about management?

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idalivered
Advisor

Re: Grid sampling

Jim, not sure what it means about management, but i think we and all of agriculture are all trying to use expensive plant nutrients in the most efficient manner possible. Grid and zone sampling are one step in the process.  I'm not a soil science or agronomy major (or even a college graduate) , but just seems like the more we know, the more questions we have.  What we think of as "cutting edge" technology will seem quite misguided in 20 years, but that's how we will get from here to there. My highest yielding farm was one that was just blanket applied with one anaysis per field. Likely one of the most profitable, too. I will continue with  variable rate sampling and applications on some farms.