Posted 10/16/2020 08:19 (#8548467 - in reply to #8548331) Subject: RE: Soil grids
garyl - 10/16/2020 07:14
Interesting discussion. I would challenge people to do this experiment. Go to what you think is a random spot in your field. Take 13 core samples in the shape of a cross 2 ft apart one in the center and 3 on each side. Test the individual core samples. Don't tell the lab what you are doing. You will learn a lot.
What is that going to prove? Have you been to your soil lab?
My answer is likely your inability to take consistent cores. Most variability comes from soil sampling, not from lab variability. Yes there is some lab variability, but most test for that regularly (again have you been to your lab?). The reason for higher core counts is to help eliminate variability of uneven nutrient from application (bcast or banded) and mechanical incorporation, or previous plant residue.
One core is not representative of a sample. Thats my whole point. The more cores you take, the more statistically accurate the sample is. Statistically, the accuracy curve really starts to taper off around 9 cores and much more so in the 12-16 core count, and pretty much flat at around 24 cores.
Less than 9 cores per sample is highly variable results imho. 12 cores from the JCB probes i use fill a bag to the middle of the sample bag full line and is a reasonable amount of time to get. I want to avoid manually mixing and then only submitting part of the soil collected because that leaves the door wide open to human errors too. 0-6" sample means you submit 6.0" cores, not 5.75" or 6.25" cores.