Articles on forages, animals, and grazing systems
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Extension Forage Specialist
University of Kentucky
Phone: (859) 257-3358
Fax: (859) 323-1952
Fertilizer is one of the main expenses in a productive grazing system. It is important to apply fertilizer and lime in accurate amounts for best forage production and financial and environmental reasons. Performing a soil test on pastures and utilizing the results to evaluate pasture fertility is strongly advised. Analysis of a soil sample will determine nutrient content of the soil including phosphorus, potassium, magnesium, sodium, sulfur, manganese, copper, and zinc. Soil pH, organic matter, and exchangeable acidity will also be included in the results. These results are used to decide what to apply and how much to apply.
Almost all farmers apply too much or too little lime and/or fertilizer when not using a soil analysis to calculate the amount needed. Applying only what is needed is essential for best plant growth at the lowest price. If too little is applied, stand yield and quality will suffer. If lime is over applied, soil pH will rise which can make some nutrients less available to the plant and cause unfavorable growing conditions. Over application of fertilizer can also be detrimental to the environment and cause contamination of surface and ground water. Performing a simple soil test can help to ensure the correct amounts of lime and fertilizer are applied to pastures.
Soil tests should be taken every 3 to 4 years in pasture areas. Separate samples and analysis should be done for separate pastures and unique areas within the pasture which may have substantial variances in nutrient content. For example, a feeding area or shaded area where livestock might spend extended periods of time build up manure and may have much higher nutrient levels. Spring and fall are the best times to perform a soil test. Earlier in the season is ideal so there is time to purchase and apply fertilizer according to test results. A soil probe, spade and knife, auger, or trowel can be used to collect samples. Samples at a depth of 3 to 6 inches should be taken in 10 to 12 different areas to give a representative sample. All equipment used to take the sample should be clean to avoid contamination that might obscure results. Samples need to be thoroughly mixed in the bucket. Soil sample bags should be filled with 1 to 2 cups of soil and should be clearly labeled. The name given to the sample needs to be easily recognizable to the area it was taken from to avoid confusion. These bags can be obtained from your local extension office. Samples can be returned to the county extension office to be shipped to the testing lab.
County agents can assist in interpreting results and developing a fertility program. For more information on how to take a soil samples, refer to AGR-16: Taking Soil Test Samples.
Fertilizer and lime are usually over or under applied when a soil test is not used. Each unique area should be tested separately and fertilizer and lime should be applied accordingly. Consider test results, history of pasture, grazing practices, and forage species when planning fertilizer applications. Spending only $5.00 to perform a soil test can save money spent on excess fertilizer and can reduce negative environmental effects. It will also reduce loss due to poor yields caused by inadequate fertility. Perform a soil test to determine correct fertilizer and lime applications.