Importance of Soil Testing for Pasture Grasses

When preparing newly established pastures or already established pastures for the growing season the first step should be collecting soil samples.  Producers who sample in the Fall and Winter have a head start on those that wait until Spring.  A soil sample can tell you many things about your pasture soil health.  That soil sample can inform the owners about what nutrients are available in the soil, the level of those nutrients,available to the plant along with the alkalinity or pH of the soil.                                                                                                                                                                                                                                                                                                       Soil Sampling 

When collecting soil samples it is important that the sample is representative of the are of interest.  If an area contains a different type of forage, has a noticeable problem, or a different soil type, you may want to sample those areas separately. To take a representative sample you first need a clean bucket and collect several sub-samples from around the pasture.  Make sure to stay away from high nutrient areas such as ditches, feeding areas, congregational areas or water troughs.  Your sample should be from the ground level down six inches in depth.  Once you have collected all of your sub-samples you will mix them together, removing plant material, to get a representative sample of your pasture.  You will need to send in approximately 1 -1 1/2 cups of mixed soil for analysis.

Results

After submission of your soil sample you will receive your results back in the form of paper copies in the mail and/or email.  These results will include the pH of the soil, lime or dolomite recommendations, levels of major nutrients including phosphorus, potassium, calcium, and magnesium, along with micronutrients including copper, manganese, and zinc.  These are all nutrients that can affect plant growth and how well the soil reacts with the fertilizer to “feed” the grass.

pH is an important factor in soils where forages or grasses are grown for livestock purposes.  When relating soil pH with fertilizer efficiency for pasture grasses, it has been shown that you will get the most efficiency when your soil pH is at 5.5.  Not only is fertilizer efficiency important, but the pH will also affect the health and hardiness of the forage or grass being grown in that soil.  The target pH for most pasture grasses is 5.5 with legumes preferring more alkaline soils with a pH of 6.0 – 7.0.

Besides pH being tested in a soil sample, the UF/IFAS Soil Testing Lab also conducts test to predict the parts per million (ppm) of phosphorus, potassium, magnesium, and calcium.  Phosphorus and potassium are two of the three components which make up commercial fertilizers when combined with nitrogen.  By testing the ppm of these two components we can better recommend rates to apply the potassium or phosphorus to the soils, therefore, limiting the amount of phosphorus run-off and being better stewards of the land and water.  With nitrogen being the limiting nutrient for forages, producers do not always need to apply potassium and phosphorus to their soils.  However, nitrogen allows for a quality forage and increased production.

The magnesium and calcium levels are measured as well.  These measurements can be used to determine if the soil has adequate amounts of these minerals.  If the pH is low and the level of magnesium is also low then the lab will recommend that the producer apply dolomite to the soil.  This will add magnesium to the soil as well as raising the pH of the soil.  If the pH is low but the magnesium level is adequate then the recommendation would be to add lime rather than dolomite.  The reason for this is that lime does not contain the magnesium that the dolomite does.  The lime that is applied is a calcium based product.  It is important to remember that it can take up to six months for lime or dolomite to fully react in soil.  It is also important to remember not to over apply lime and dolomite due to the fact that it is easy to raise a pH but extremely difficult to lower the pH in soil.

Summary 

Soil sampling is an important component to pasture management.  Research has also shown that for Bahiagrass tissue tests are also important.  Through research it has been found that the tissue of bahiagrass can hold phosphorus when it appears to be inadequate in soils.  The thought is that since the root system grows so deep that they can take in phosphorus through the water at the deeper depths that will not show up in the soil test.

The soil and tissue tests are conducted at the UF/IFAS Soil Testing Lab.  The costs for a soil sample is $7 per sample and for a combination soil and tissue test the cost is $15 per sample.  The Manatee County Extension Office offers soil testing for $3 per sample and tests for pH and $5 for pH and soluble salts testing for homeowners through the Master Gardeners.  Spending a few dollars on a soil sample can save a producer a large amount of money if done on a regular basis.  When the soil sample test results are used for fertilization it reduces the amount of phosphorus run-off into our waterways improving the environmental stewardship of the land.

Any livestock producer who has further questions can contact Christa Kirby, Manatee County Livestock Extension Agent at 941-722-4524.  Any homeowner who would like to have the soil for their lawn tested can contact the Manatee County Master Gardeners, 941-722-4524.

** Adapted from

Silveira, Maria L. Soil Fertility for Forage Crops. 18 May 2007. UF/IFAS Range Cattle Research and Education Center, 2008