Food Plot Soil Amendments – How to Interpret Soil Test Results

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Soil Test Report: PH is the Most Important Characteristic to get Right

I recently received a message from a client who, after sending in his food plot soil test and getting the result was asking me to get him a delivery of lime.  He told me his test came back with a 6.2 pH, close to what it had been before we added a truckload of lime last year.  My investigation uncovered the problem: the soil sample was taken with a shovel and much of the sample was below the depth affected by the lime application.  I find it is a good investment to purchase a soil probe.  Take your samples from multiple places in the field and only go about 6-8 inches down.

pH is important for soil microbial action, which is the most important part of the soil food web and takes place mostly in the O and A horizon – not very far below the surface where oxygen, nitrogen and carbon are available.  Roots create there own pH in the rhizosphere as the root pushes down into the deeper soils looking for nutrients and moisture.  So, I don’t get too concerned with deeper soils pH.

Acid soils are caused by fungal activity and organic matter content (forest soil is high in fungal population and organic matter), parent material (sandstone and shale derived soils are going to be acidic and limestone soils are not, and the application of Nitrogen fertilizers.  The breakdown of N fertilizer in ammonium form releases H ions, which is what acidity is.

I like to get my N from the atmosphere by growing lots of legumes.  The air is mostly nitrogen and there is tons of it available for free over every food plot!  Why pay for it?  It also should be mentioned that our favorite fall foods – the brassicas will bring N that has leached down into deeper soil and bring it back to the surface in the form of proteins in the plant material, making it available in the spring for new growth.

More is Not Always Better

I still have clients who feel that the more fertilizer you put on the better.  If you think that way, stop it.  There is a balance of molecules in the soil that plants need to grow and stay healthy.  Too much of one thing leads to disruption in the uptake of another.  For instance, too much magnesium will interrupt uptake of Potassium.  Also, much of the nitrogen that is applied to soil is leached into ground water and runs off into streams causing serious pollution.  Last but not least, the cost of fertilizer can be a waste of money when you apply more than is necessary.

Only apply fertilizer according to the soil test recommendations for the crop you are planting.

Ok, so lets take a look at this soil sample.2016-04-11_15-45-15

Not bad.  The first thing we notice is the 6.0 pH.  Referring to the above discussion, we decided that we should test again using the upper 6 inches of soil and the pH came in around 6.2.  Healthy soil should have a pH of 6.4.

The other thing that stands out is the very good organic matter.  I credit the fact that we had a good operator on the clearing job and also that we applied poultry manure last year.  Above 5 is a good organic matter level.  The CEC (cation exchange capacity) is a little low.  This number is a relative number and depends a lot on the soil texture and the organic matter.

A sandy soil with low OM is never going to have a very good CEC.  A clay loam soil can be expected to have a higher CEC.

What is CEC and why is it important?

Most of the nutrients we are intersted in are cations or positively charged ions when they’re floating around in soil.  They attach themselves loosely to clay particles and can be exchanged for by the plants.  The plant root will send out hydrogen molecule to exchange for a nutrient element.  Calcium, potassium, ammonium, sodium.  The root can also exchange a hydroxide OH for an anion nutrient molecule which is also attached to positively charged sites on organic matter.  Anion nutrients are phosphorous, magnesium, sulfer.

The percent base saturation of the soil nutrients are provided in my Penn State soil lab sample results.  Test Report for Post

This is the saturation level of the cations that are occupying the sites made available by the CEC.  This is an easier number to make sense of since it is a percentage of the capacity to hold the nutrient.  So we can have steady guidelines.  For instance, the most important figure is the Base saturation of Calcium.  Calcium is important in many functions of the plant and the biosphere.  It should be over 50% and can be as high as 75% in clay soil.  Potassium level should be around 4-5%, sodium should be less than 1%.  The rest of the percentage of sites available are for other nutrients.  There are 14 essential nutrient elements, maybe more, that are necessary for healthy plant growth.  One of these is molybdenum – essential for the production of nitrogenase enzyme that bacteria develop in order to fix nitrogen for the plant.  As you can see in John’s test report, they are asking him to make sure the soybean seeds are treated with Mo, that’s why.

So what’s the plan?  I suggested to John that we do not apply fertilizer but apply another truckload of lime and poultry manure.  Pulling the pH up just a little and providing nutrients in organic form will probably take care of any deficiencies he has there.  And, its cheap and easy to apply – just write a check.

He should test again in the fall and if necessary apply only what he absolutely needs for fertilizer then.

Now, take a look at my other client’s test report for a hay field on his property.

Test Report for Post

The Importance of Organic Matter

soil test

A comparison of high organic vs low organic soil from the same area

Notice his organic level is very low.  This is probably due to the fact that this is a field that is cut for hay and the plant material is taken to another part of the farm for winter feed.  Notice how they describe base saturation as the percent of the CEC – which is a good way to describe it.  The levels look good but the CEC is low, so how available are these nutrients?  Soil OM should be built up through mixing a good cover crop and grazing the pasture for a few years instead of cutting hay.  Having livestock on the ground turning course grass into manure is the best way to build soil health.  Notice from the photo of the soil

the color of the field soil with low OM compared to the color of the forest soil next to it.  You can easily see that the OM has been removed while the forest OM is very good with a dark humus layer.

So, what’s my recommendation – you guessed it, another truckload of lime and chicken shit.  That and a good soil building legume mix with grazing will build that soil back to where it should be.

PS

I just got my soil test back from the field in NY you see on my Youtube videos all the time.  The last two years, we planted legumes – clover, soybeans, peas, as well as some sorghum and brassicas.  As you may have seen, we terminated the plot with cows (the farmer that owns it is a breeder) and spun some more brassicas on for the fall.  As you can see, without any soil amendments for last year and using no til planting and livestock for management we have a soil test that shows it does not need any lime or macronutrients and is actually excessive on K.

SoilReport5acField2016

What I see on this soil test report is that we definitely do not want to apply any fertilizer. That would not only be a waste of time and money, but would probably harm the crop.  Excessive K can reduce the uptake of boron, the micronutrient that is most important in N – fixing by bacteria.  Too much K can also interfere with the uptake of Magnesium, which in turn, can cause health problems in plants and also in the livestock that eats it.  We may want to plant some alfalfa in this field to take up the excessive K as it is a big user of this nutrient.

The micronutrients are a tad low which has me thinking that it may be a good plan to apply dissolved sea salt or seaweed fertilizer as a spray application.

One of the reasons this field is in such good condition is that we do not take any of the crop away other than what is used to build venison and beef bodies.  Most of the material is shat back onto the land where is was eaten, building soil and keeping the nutrients on site.

I once was severely criticized by a hunt club for putting up electric fence and grazing some horses in a large planted forage area.  Grass had taken hold there and it had become a weed.  Horses live on grass, deer don’t, so they helped keep the course grasses under control.  Trying to argue with ignorant people is a fool’s errand.  The moral here is to think outside the box of what most folks think about planting stuff.  Food plotting is more like organic farming than it is traditional farm practice.  If you build soil health by using multiple crops, double cropping and using grazing instead of spraying and fertilizing, you will have more productive plots.

And keep in mind that deer know what is nutrient-rich.  If you have great nutrients and a variety of plants maturing at different times with new growth always coming up, you will attract more deer than anything else will and grow nice big ones for the table and trophy room.

 

 

About the Author:

Wildlife habitat manager and consulting forester from Central PA. Studied environmental Agriculture specializing in wildlife management and Forestry. B.S. Agriculture, Masters degree in Forestry. 30 years experience in land investment, forestry and wildlife habitat improvement. Currently working as a Farm Bill Forester for Pheasants Forever on Game Commission and Golden Winged Warbler Initiative.

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