Tips for Understanding Soil Sampling | Great Days Outdoors

Soil sampling helps a person better manage land

 

Fertilizer and lime recommendations can be confusing. All the different numbers and suggestions can really make it difficult to understand what soil and crops need to perform best. Let’s simplify things with a few quick tips to understanding soil samples.

When it comes to soil management, pH is the first thing people need to get right. Although some crops are more tolerant of acidic soils than others, a food plot will perform best with a pH of 6.5 to 7.0. Lime is relatively inexpensive and is the key to successful plots.

For perspective, a plot with a pH of 5.5 is 10 times more acidic than one at 6.5. More than 50 percent of fertilizer added to a plot with a 5.5 pH is wasted because it is not able to be used by the plants. Applying one to two tons per acre of agricultural lime is very common to get plots where they need to be.

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Soil Sampling for food plots.

 

What Does It All Mean?

Remember that the three numbers on bagged fertilizer (N-P-K) are based upon 100 pounds, not 50. In a 50-pound bag of 13-13-13, there are 6.5 pounds or units each of actual nitrogen (N), phosphorous (P) and potassium (K). If your sample says you need 40 pounds each of N-P-K, you would need 350 pounds per acre of 13-13-13. This would give you 45.5 pounds of N-P-K.

An advanced soil test is needed to determine current levels of micronutrients like copper, iron, zinc, boron, etc. These micros are usually not present in bagged fertilizer. Although they are needed in very small amounts in comparison to the macros (N-P-K), it can be worthwhile to do an advanced sample every three to four years to keep the micros up to date.

“Keep in mind, even if a soil sample comes back with a pretty acidic pH reading like 4.5 to 5.5, the plot is not a lost cause.”

As a general rule of thumb, cereal grains, corn, and brassicas are nitrogen lovers. Legumes, such as clovers, peas, beans or alfalfa, fix their own nitrogen from the atmosphere and need very little at planting time.

For example, once established, clover can be fertilized with a common 0-20-20. At planting time, a low nitrogen blend like 5-20-20 can be used to give the young clover a small dose of nitrogen while it develops a root system and begins to affix its own from the air. On the other end of the spectrum, corn can use 100 to 200 pounds of nitrogen per acre for a maximum yield.

Keep in mind, even if a soil sample comes back with a pretty acidic pH reading like 4.5 to 5.5, the plot is not a lost cause. A couple of tons of lime per acre can really change how successful your food plot plantings will be.

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Fertilizer or Lime?

Lime is relatively cheap but is often the most overlooked tool for growing good crops to attract and hold wildlife. Continuing to spread fertilizer on highly acidic soils can be counterproductive and frankly, somewhat a waste of good money. I would much rather see someone with pH levels below 6.0 spend some of the food plot budget on lime rather than fertilizer.

The time it takes for lime to begin to breakdown and start to neutralize the acidity in soil can be dependent on several factors. One of these is how fine the lime has been screened at the quarry. Lime that is screened through a very fine mesh is more of a powder consistency and will begin to breakdown in the soil quicker than a more coarse lime screened through a larger screen.

Once you have added lime to a plot according to a soil test, it could be two to five years before you need to spread more lime. The amount of time in between applications can vary with different soil types, rainfall amounts, and other factors. Obviously, very sandy soils typically leach lime and other nutrients quicker through the root zone than heavier soils with a higher clay content.

Spreading it Around

Be sure to contact your local farm supply or co-op to spread lime for you. If your plots are accessible with larger equipment, they can spread the lime for you very efficiently.

Another option is to have the lime delivered and dumped on your property and spread it yourself. Lime and fertilizer spreaders can often be rented from a local co-op or extension service very reasonably if people have a means of loading it themselves.

“Be sure to contact your local farm supply or co-op to spread lime for you.”

Using pelletized lime is an option when access to the plot is restricted by terrain, trees, creeks or other features that can prevent large equipment from getting to the plot. Pelletized lime is a slightly different form of lime compared to agricultural powdered lime. Ag lime that comes from a quarry is called dolomitic lime.

As stated earlier, the time it takes for lime to break down and begin neutralizing acidity in soil is directly related to the particle size, which is determined by how fine a mesh screen the lime is ran through before sale and transport. Pelletized lime is a form of calcium carbonate.

I personally prefer to use ag lime when it is available and can be efficiently spread. Generally speaking, the cost per acre to have the correct amount spread according to your soil test is significantly less when using ag lime being spread by a co-op or farm service.

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