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| I think the chemical tests in the lab are fairly consistent though the repetitive drudgery doesn't attract the best of minds to the work. The trouble with sampling is that its based on the concept that the soil is homogeneous, that its been really well mixed. Through with strip tilling, plants in rows, and nutrient application with coulters, slot cutters, and spinners and quit plowing, disking, and field cultivating and the field is FAR from homogeneous, if it ever was. I'm sure a row of corn plants does take nutrient from as far out as the center of the space between the plant rows, but there are a lot more roots IN the plant row than between the rows so the plant uptake isn't constant every inch across the rows. No doubt there are differences between plant root vigor within a variety and much larger differences between different varieties. Just look at how often a few corn stalks will be head and shoulders above the rest of the field. Some numbers obviously are blends, not pure breds. Then within the nutrient applications, the particles are not all the same size, whether from the best of chemical suppliers or locally produced manure the density of nutrients varies by the inch.
For 20 years on my farm the pH has been about 6.8 despite an application of lime about 1989 when I bought the place. Until a couple years ago the tenant's soil tests started showing a dropping pH. Is it due to applying AMS or is it sampling? He's strip till, I last planted no till in 2008. With the concentrations of nutrients from applying them while making the strips, I have far less confidence in sampling because the field is getting stratified. 8" strips every 15" get the work, and the in between only gets extracted by extended roots but doesn't get recharged. RTK gets the strips precisely the same place every other year. Its probably that today applying nutrients by theoretical removal plus a fudge factor may be closer to the long term truth that might be checked occasionally by skipping certain applications. And micros just need to be applied occasionally because soil tests are at best inconclusive and sometimes don't represent the plant uptake at all.
Gerald J. | |
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For the sake of discussion........
