Posted 10/17/2020 16:19 (#8550439 - in reply to #8549727) Subject: RE: Soil grids
Ron..NE ILL..10/48 - 10/17/2020 04:58
This has been our experience also. Again, this may be a "here" thing. But let's say we have a 1/4 mi x 1/2 mi straight edge 80. We have several. Maybe 3 soil types (here) with the predominant making 70% of the 80. Slope will be 0-1 degree. Field would be adequately drained. Certainly not uncommon in NE IL.
So, how many points would be sampled (not probed, sampled) in zone testing? Would all zone testers choose the same number of samples? If not, is it possible to choose the wrong company to utilize zone testing?
In our typical "little squares" of 2.5 A grids, we'd have a minimum of 32 grids in that field. Surely in our 330' x 330' tests we would hit all the zones, wouldn't we? There would be no doubt.
That field would cost about $500 to have gps tested with recs & prescription files supplied for our spreader. My spreader does seem to like to spread squares. I don't have the new "half-width" disconnect now being offered. Not sure that is necessary anyway.
Covid mask effectiveness on controlling the virus certainly seems debatable. Not by true believers, but by a big % of the population that is skeptical.
JD vs IH combines is also debatable. I doubt you'll find many owners of $500,000+ combines these days saying "I don't care which I get, they're equal....".
Point is, whichever one is doing is probably OK. However, the other side of all these choices seem to chastise those that don't utilize their stance.
Everyone is going to zone differently and choose where to sample. Here is what I do and compared to a 2.5 acre grid, ssurgo soil type, Aerial image derived soil type. In this case the 80 has a ridge running through that most fields here don't have, so I sampled 4 zones instead of the more normal 3 zones. Usually I have 7 zones and sample zone 3 (zones 1 &2 are extreme low or ditch bottoms and sometimes have water standing), 5, & 7(the very best) and in this case zone 12-13 (the ridge). I dont sample points like if it were grided. I sample 2-5 cores out of an area of a zone a few feet apart. Often I take 3 cores from 4 areas of the same number zone across the field. So I'm after 12 cores that represent each zone for a total of 36 cores (or in this case 48 cores). If I were to grid, I would select a point within the grid that best represents that grid (not necessarily the middle) and then pull 10-12 cores around that point. So if grided, I would pull 320+ cores. These 48 cores take me about an hour to get, more driving and less cores per spot vs grids, so about 1.25 min per core on avg. I drive around the field 3 times basically, doing the best zone, then middle, then poor separately so there is zero chance of dropping a core in the wrong bucket. If I did grids and for arguments sake could take 2x cores in that 1.25 rate, it would take me over 3 hours to sample. Realistically, it would be about 4 hours good cores. So 4x the time/cost to grid vs zone. I do complete analysis and that costs me $26/sample, so about $100/field by zones vs ??? Less than a complete costs less, but 32 samples (so $5-??/sample x 32) 32 complete samples would be over $800. We don't typically have to lime, but if we do its 1-3 of my 7-13 zones. So were are just adjusting NPK and population I can sample every year after each crop, write accurate recs and build maps for about $10/acre per year for the same money as doing a grid once every 4 years and guessing what 4 crops are going to remove based off of 1 year grid test. I dont think anyone that grid samples for a living is going to spend 4 hours sampling an 80. That means less cores, less care for each core, etc. It means some analysis less than a complete. This all equates to less quality of a product imho.
I have attached a few pics of this field with ssurgo soil lines and 2.5 acre grids over my zones. Many of the grids have multiple soil types or multiples of my zones. Often several grids have poor, middle, and best zones in a single grid (often as many as 25-30% of grids) Thats alot of known error by forcing grids and throwing out known zones.
1st pic is ssurgo showing like 7 soil types, but in reality many are closely related, so I would say more like 3 soils.
2nd pic is aerial derived soil types. Shows quite a bit more accuracy than ssurgo based zones for those that "zone" by soils.
3rd pic is my zones with grids
4th pic is my sample points
5th is a corn yield map that is cleaned, adjusted, and then smoothed for zone purposes. 15 bu to 299 bu with field avg of 185 bushels. Again this isn't most common here with this gravelly ridge. But often we have drown out or severe wet that is less than 100 bu to zero and best zones getting 220-270 bu highs with 160-225 field averages.
6th is midwest lab results lo3 is poor, lg5 is middle, dg7 is best, rh13 is ridge.