Soil Sampling & Soil Fertility

July 2009
Christa L. Carlson-Kirby - Manatee County Extension, Livestock Agent II

We conduct soil tests to find the nutrients in the soil which are available to the plants. Through the soil test we can also find out the salinity or pH of the soil and any elemental toxicity in the soil. Any and all of these components of the soil will affect the production of the plant material grown in the soil.

When a soil sample is collected it is important that the sample be representative of the area of interest. If an area contains different forage, have a clear problem or a different soil type you would probably want to sample that area separately.

pH is an important factor in soils where forages are to be grown. When relating soil pH with fertilizer efficiency 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 soil pH will also affect forage production and water use efficiency. 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 determine the concentration, in 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 soil concentrations, we can better recommend rates to apply the Potassium or Phosphorus to the soils, therefore, limiting the amount of nutrient losses. Because Nitrogen is usually the most limiting nutrient for forages, producers do not always need to apply Potassium and Phosphorus to their soils.

When sending a soil sample to the lab, Magnesium and Calcium levels are measured as well. 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 for lime rather than dolomite. The reason for this is that lime does not contain as much magnesium as dolomite. The lime that is applied is a calcium based product.

Soil sampling is an important component to pasture management. Spending a few dollars on a soil sample can save a producer a large amount of money in the future if done on a regular basis.


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

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