Sunday, April 15, 2012

Don't Guess, Soil Test

I get a lot of soil sample results in the mail and email. This one comes from a farmer who just bought this farm and he wants my help to make it yield profitably. His corn made 120 and beans 30 last year. He applied 100 lbs of MAP or phosphorous and 100 lbs of potash before last year's first crop and again afterwards.

The columns are difficult to put in this blog so they are understandable. It starts with the lab number, sample number, water pH of the soil, organic matter percent, organic matter in pounds per acre(gives you an idea on humus content, few labs do this, this one is low.) Then there is a saturation number and the typical chemical symbols except for CEC which is an unknown term called Cation Exchange Capacity, or how many positive and negative charges the soil can hold. Those CEC's are typical for his soil and mine and the better soils have 20, 30 and above. They can hold more nutrients but require more potassium.

LAB# Smple WpH OM% OM# SAT P K Ca Mg CEC H Ca Mg K S Zn Fe Mn Cu B
399766 9 7.5 2.2 44 37 120 12 1.8 66 99 1.4 0.4
399767 10 7.6 2.3 45 25 102 12 1.8 66 99 1.4 0.4
399768 11 7.5 2.1 43 17 114 12 1.8 66 99 1.4 0.4
399769 12 7.4 2.4 48 16 174 12 1.8 66 99 1.4 0.4
399770 13 7.3 2.8 56 13 183 10 1.9 47 130 1.3 0.6
399771 14 7.4 2.2 44 17 141 10 1.9 47 130 1.3 0.6
399772 15 7.7 2.4 47 11 102 10 1.9 47 130 1.3 0.6
399773 16 7.5 2.6 51 25 194 10 1.9 47 130 1.3 0.6
AVERAGE 7.5 2.4 47 20 141 11 1.9 57 115 1.4 0.5

The first thing I saw was the high "water pH." 7.0 is neutral and 6.5 is about ideal for most crops. He said the former owner applied a lot of lime. It is obvious he did! I told him he will probably never have to lime again in his life but maybe his 12 year old son will.

Now, this probably looks like gibberish to most of you but to farmers and agronomists who work with soil test results regularly, this makes some sense. This a Mehlich III extraction which is most common but not the one I use. These results shown won't be the same numbers I get from my lab but they are a place to start.

The P and K columns which represent lbs of Phosphorous and Potassium available for the crop are on the low side, so the farmer did well putting on what fertilizer he did. I recommended a tissue test from the crops to get a better idea what the soil balance and micro nutrient uptake is. He has part of it in wheat so he is going to pull tissue and soil samples today and get them to my lab. The results will help me see what to recommend next.

Soil testing is not exact because we are sampling such a small portion of each field compared to the tons of soil underneath one sample. We do have enough information after 100 years of soil testing to get the crop into the "ballpark" as far as nutrient needs.

If you haven't sampled your garden or farm for the last few years, I suggest you do it now. I am willing to help any reader who wants a prettier lawn, better garden or more profitable crop.



  1. Ed

    Great post here! Thanks for keeping people informed and educated about soil testing. It's refreshing to read posts like this.


    Brent Pohlman
    Midwest Laboratories

  2. It was a crude last minute post Brent, but I thank you for your positive comment! I like to hang around positive people like you! If a reader goes back to my first blogs and picks out the similar titles, it may make more sense. I need to get into the habit of linking back to those relevant past blogs!