Composite soil testing

[craig]

I find it interesting that the debate rages on some new technologies and their value( CTF and variable rate fertilizing) because we don't have proven research. At the same time we harp on the value of composite soil testing which can only be classed as a very inexact science. In research we think it's very important to reduce variablity yet we randomly travel a field with numerous soil types and profiles and assume the results of composite sampling are a representative average of the field. A composite soil test may be better than a educated guess but for the cost leaves lot's to be desired.

[FarmRanger]

Agreed Craig,
Even with benchmarking, composite tests just give you a vague idea where "average" nutrient levels are.

The last few years I've tended to make my best guess as to what yields might be, and fertilize to replace the nutrients I'm taking out.

Experimenting a bit with variable rate applications, but I'm still on the fence as to whether we should be putting less fertilizer on less fertile areas of the field because they yield less.

An example would be an eroded knoll that produces very little; it will never produce more if we starve the plants seeded there because historical yields in those areas indicate less fertilizer should be applied due to lower production potential.

Thoughts?

[craig]

FarmRanger
We have been using variable rate for about 3 years and
we still struggle with yield potential. There are some
good fertilizer savings to be had from not over
fertilizing lower yielding land yet we sometimes see a
fertilizer response on that land even in a dry year.
Thinking maybe split application might be a better
way to go on light sandy soils. Still lots to learn but at
least we are thinking this stuff through vs what we did
in the past.

[skip]

We are thinking alot more about these systems with higher grain prices and more expensive fertilizer prices...at least it pays to do some of the research. We are looking for Maximum Economic Yields...borrowed that term from an agronomist speaker I heard.

[AG_guy]

This is how i now do my soil testing. I used to go up and down the field taking random samples, I never really believed in benchmark soil sampling and i have a diploma in precision Ag.

Now what i do is find a location in the field that represents the rest of the field. GPS that point and soil sample a 100 x 100 foot square. I do 15 random sample in that area.The reason being is that out of that bag of soil the lab only uses roughly 2 tablespoons of soil to base there results on. So if you test that same 100 x 100 square you will know what happening there and you will get better results. Then every year you can look back and see what happening and know ig nutrients are increasing or decreasing. It's a more controled method of sampling.