Phosphorus is a naturally occurring element that is one of 16 elements essential for plant growth and animal health. Research has documented that applying phosphorus in fertilizers or manure increases crop growth and yield on soils that are below critical agronomic levels, as measured during routine soil testing. Although the economic benefits of phosphorus fertilization on crop production are well-documented, too much of a good thing can be detrimental to the environment. Excessive soil phosphorus is a potential threat to water quality.

Acid soil limits crop yields on many Virginia farms. This soil acidity can be directly toxic to plants, but more often it reduces the plants' efficiency at nutrient utilization.

Most Virginia soils are acidic and require lime applications at three- to five-year intervals. Maintaining the correct soil pH has several benefits, such as encouraging healthy root development and making sure nutrients in the soil are available to the plant. For example, low pH can cause aluminum toxicity and can decrease phosphorus availability.

The Shenandoah Valley of Virginia and some other regions produce more manure nutrients than local crops need. This manure has traditionally been applied to row crops and overapplication has led to soil-test phosphorus (P) being well above agronomic optimum in many cases. In 2008, it was estimated that nutrient-management regulations now require that approximately 85 percent of poultry litter be applied off poultry farms, as they do not have sufficient land to beneficially recycle their manure nutrients.

Crop production has increased dramatically over the last few decades, much of which has been due to the widespread introduction of chemical fertilizers starting in the mid-1900s. Matching fertilizer application rates to crop needs is an essential component of optimizing crop production. However, different crops in separate fields will require varying rates of the major nutrients – nitrogen (N), phosphate (P2O5), and potassium (potash, K2O) – due to variations in soil types, soil test phosphorus and potassium levels, and nutrient ranges of different crops.

Animal manures are a good source of nitrogen (N) and phosphorus (P) for agricultural crops, but they have an imbalance in their N to P ratio, so that if they are applied to meet crop N needs, then P is overapplied. For many years, manures have been applied to meet crop N needs, which has resulted in some soils containing more P than crops require, leading to environmental concerns. Regulations have been developed to limit P losses from manures and soils high in P by moving manure nutrient management from an N basis to a P basis.

The only way to accurately predict lime and fertilizer needs in forages is through soil testing, as explained in “Soil Test Note No. 1 – Explanation of Soil Tests,” Virginia Cooperative Extension publication 452-701. See www.soiltest.vt.edu.

If your Soil Test Report indicates that one or more trace elements are needed, then go to the related sections in this note for information on the recommended trace elements and the specific rates and methods of application. Apply only those trace elements that are recommended, and only at the recommended rates!

their yield potential. Research has documented that applying fertilizer phosphorus increases crop growth and yields on soils that are naturally low in phosphorus and in soils that have been depleted through crop removal. Crop fertilization represents the greatest use of phosphorus in agriculture today.

Correctly collecting a soil sample is one of the most important steps in a soil testing program! The reliability of a soil test can be no better than the sample submitted. For results that can be depended on, it is vitally important to take samples that accurately represent the soil in your fields. When one considers that a one pound soil sample must adequately represent millions of pounds of soil in the area being sampled, the importance of doing a good job of sampling becomes apparent.

Your Soil Test Report and related Soil Test Notes referred to on a report will help you assess your plant’s need for fertilizer and lime.

The procedures for soil analysis used in the Soil Testing Laboratory were established in the early 1950s. A routine test, consisting of eleven separate analyses, is performed on all samples.