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Post by JoshuaGA on Dec 1, 2011 20:15:14 GMT -5
Need a little guidance on grid sampling. Anyone wish to share their experiences, recent publications, tools I need, etc. to grid sample. Got a field we want to mess with. Neighbor grid sampled a field and put a bee in dad's bonnet over it.
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Bristol Hillbilly
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Post by Bristol Hillbilly on Dec 2, 2011 5:23:15 GMT -5
The sampling I do myself I just take my handheld gps and grid it off in even sections. Ex 30 acre field I will measure width divide by 5 and take 6 grid samples. The outfit that does some others for me measures off 3.5-4 acre grids and samples it that way. They have been doing some for me for 15+ yrs and have been very happy.
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Post by Dave-ECIA on Dec 2, 2011 14:41:48 GMT -5
I'd suggest another route.
We have started to sample by soil type. Pull out your soil maps and overlay it on the field. Be sure to sample each soil type. If the field doesn't have many soil types, a 2ac grid sample tends to tell you the same thing. Over and over again.
I was never a fan of laying a grid over something so non-geometric as soil within a field.
Keep track of the points where you sampled by GPS, but pull them by soil type. You might be surprised what you find.
Do you have a way to mark the sample spots with GPS?? It's important that you go back to those same sample locations, or as close as humanly possible, in the future.
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Bristol Hillbilly
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Post by Bristol Hillbilly on Dec 2, 2011 17:44:16 GMT -5
Dave I right teh gps coord. down on map so it can be replicatied in two years. I have some fields that have 4-5 different soil types in it and some that have 1. Can you go a little deeper in the logic behind this. I realize some of my soil types are alot better than others but the soil map shows me that. Are you adjusting fetilizer to yield potential due to soil type?
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Post by Dave-ECIA on Dec 2, 2011 19:55:19 GMT -5
I'm operating by using the assumption that any given soil type has a maximum potential yield.
Your question skips ahead a little. Let's take this a piece at a time. I have a 99 acre field that has somewhere in the neighborhood of 4 major soil type areas, and 3 small areas of other soil types for a total of around 7 soil types represented in the field. If I were to go by the standard grid of 4ac, I would have 25 unique soil samples.
By sampling by soil type, we pull something like 13 areas. Some of the soil types are differentiated by slope.
Matching yield mqps to soil type, its almost uncanny how the yield variation matches the soil type map.
What I'm trying to find out is this. Do my high and low yield areas show an excess or lack of fertility, or are they consistent in fertility and the yield varies solely due to the inherent yield potential of that soil type.
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Bristol Hillbilly
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Post by Bristol Hillbilly on Dec 3, 2011 0:06:52 GMT -5
So if all things are equal ex sufficient fertility to raise 200 bu corn and x soil type raises 100 then you are taking fertility out of the equarion? That makes sense . I have noticed on my soils that even in some years the poorest soil types will surprise me wondering where the yield came from. I should be getting my maps back soon I will take a look at that. I'm sure on some the line on the yield map will corelate exactly with the soil maps.
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Post by Dave-ECIA on Dec 3, 2011 0:17:27 GMT -5
Yes, I'm trying to take fertility out of the equation and see if the variation is solely due to soil type. The next step will be what to do about it.
Where it really gets interesting.... take your yield maps and overlay multiple years, corn and soybeans, on the same field. Generally, I see the yield variation across the field is the same in both crops and follow the soil types. I have to remember those areas that are wet, compacted, etc, but overall they match up pretty well.
Keep in mind, we broadcast spread these fields forever, so we built up the fertility on the low yielding areas, and probably lost a little on the high yielding areas.
Now that we are sampling by soil type instead of block grid, we are seeing it more clearly.
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Bristol Hillbilly
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Post by Bristol Hillbilly on Dec 3, 2011 9:09:14 GMT -5
Do you have a trip level on some of your tests? What I mean on the ones hired done, we don't put any P down on anything with a P test over 60. Some of the ground being old dairy have P test extremely high. We have saved alot of money over the years by doing this. When the level gets below 60 then we start putting maintenance on. I would think by doing it the way you are the CEC should corespond exactly to the soil types. Does this happen or are the soils so close in similarities that it is not as profound as one would see going from clay to poorer sandy soils?
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Post by Dave-ECIA on Dec 3, 2011 19:24:17 GMT -5
P1 at 50 is where I've been drawing the line. Above that, no P is applied.
CEC is something I'm finding that I don't know enough about. Generally speaking, the higher our CEC, the higher the yield potential. The differences within a field are more subtle, maybe varying from 13 to 18. I can roughly take the CEC x 12 to 14 and estimate max yield with what we're doing now.
One of these years, I'd like to hire somebody to drag a Veris sled across a couple of the fields I see variation not explained by fertility or soil type.
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Jefe™©
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Post by Jefe™© on Dec 3, 2011 21:48:39 GMT -5
CEC is something I'm finding that I don't know enough about. Generally speaking, the higher our CEC, the higher the yield potential. The differences within a field are more subtle, maybe varying from 13 to 18. I can roughly take the CEC x 12 to 14 and estimate max yield with what we're doing now. I probably don't know enough about cations but around here it seems the higher the CSR is the lower the CEC score is. That would be the opposite of what you are seeing with the higher yield potential coming from your higher CEC soils. Also, is your 12-14 x the CEC a universal number or is that something that seems to work on your farm? It clearly doesn't work around here with CEC numbers ranging from 25-33. Shoot, that's a yield potential of 300-450.
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Post by Dave-ECIA on Dec 3, 2011 22:35:35 GMT -5
It's just a number that I use. My best producing soils have a cec in the 18-19 range. My poorer areas are 13ish, excluding some sand ground we have.
The high cec soils are usually tama- muscatine soils with a CSR above 90.
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Jefe™©
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Post by Jefe™© on Dec 3, 2011 23:13:01 GMT -5
I've been doing some research since I last posted. Lots to be learned, that's for sure. Thanks for sparking my interest in cations and the exchange process again. Maybe if I keep reading about it, it will absorb into my mind instead of adsorbing with the chance of being washed away. I came across this site. Haven't looked at other pages on the site but read this page and it seemed to help me understand better. www.soilminerals.com/Cation_Exchange_Simplified.htm
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Bristol Hillbilly
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Post by Bristol Hillbilly on Dec 4, 2011 9:01:15 GMT -5
Dave What is a veri sled?
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Post by Dave-ECIA on Dec 4, 2011 11:07:12 GMT -5
A Veris "sled" is a towed unit that has coulters that penetrate the soil. Those coulters use electric conductivity to measure subtle differences across the soil profile. I've heard these units can do a pretty good job of simulating the differences in CEC within the soil and will give you a map of those differences. It would be interesting to see. It doesn't measure CEC, but conductivity and there are some parallels between the two. It might do a better job of picking up subtle changes in soil type that are hard to pick up with soil tests or color changes. www.veristech.com/products/soilec.aspx
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Post by iadave on Jan 25, 2012 23:16:31 GMT -5
The problem I have with the grid sample is if you hire it done the sample may come from a silted in area by a terrace and not be representative of the area. I look at the soil while I go through the field and take samples where soil types are different and if an area has been treated different. I also check if there is an unexplained area with poor yield. For example I had one area with good soil consistently poor yield. My fertility was down there. I have had my fertilizer custom applied for several years and suspected they had been forgetting the short rows. Well when they applied I checked and guess what? I do right down my gps coordinates where my samples come from.
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