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Supercal lime fact sheet6/7/2023 Buffer pH measurement reveals how much potential acidity needs to be neutralized by the lime. In order to accurately determine the amount of lime necessary to neutralize soil acidity to the desired level, the buffering capacity of the soil must be measured. If the soil pH level is below the optimum for the desired crop, liming may be necessary (Table 2). Soil pH measurement reveals the amount of active acidity (free hydrogen ions) in the soil solution and whether or not lime should be applied. Soil testing performed every two to four years should be adequate. Because soil pH levels change slowly in a natural setting, soil analysis does not need to be conducted every year. Soils sampled during a dry period may result in lower pH values, and conversely, soil samples collected during an excessively wet period may result in higher pH values. Avoid collecting soil samples when the soil is excessively dry or wet. Soil water content and resulting salt concentration at the time of soil sampling can affect pH measurements. For tilled soils, soil samples should be collected to a depth of 8 inches, and for no-till soils samples should be collected to a depth of 4 inches. Soil pH measurement is a routine analysis conducted on almost any soil sample submitted to a soil testing laboratory. Soil Sampling and Testing to Determine Soil pH and Lime Requirement Pounds of calcium carbonate equivalent lime needed to neutralize acidity produced by application of various nitrogen fertilizers (nitrogen rate of 100 lb N/A) (adapted from Havlin et al., 1999). The amount of lime required to neutralize the acidity created by various nitrogen fertilizer materials is given in Table 1. Ammonium-based fertilizers release hydrogen when oxidized to form nitrate, contibuting to soil acidity. Roots of high-yielding grain and forage crops remove basic cations from the soil and release hydrogen into soil solution to maintain an ionic charge balance within the tissue. High yielding crops, applications of certain forms of nitrogen, and other agricultural practices also contribute to soil acidity. Over time, this continuous removal of basic cations is faster than is their replacement from weathering minerals, resulting in acid soil conditions. These basic cations include calcium (Ca 2+), magnesium (Mg 2+), potassium (K +), and sodium (Na+). Soils that form under high rainfall (conditions like those in Ohio) are subject to extensive chemical weathering and leaching of basic cations that are replaced with H + and other acidic cations (Al 3+ and iron ). Soils of western Ohio are mainly derived from glacial deposits rich in calcitic (calcium carbonate) and dolomitic (calcium-magnesium carbonate) minerals and are less likely to be acidic (Ohio History Central, 2005). Soils in eastern Ohio are derived mostly from sandstone and shale parent material that are low in carbonate minerals and are likely to be acidic. Soils that developed from parent materials low in carbonate minerals (calcium/magnesium carbonates) are usually acidic. Soil parent material and the climate under which a soil was formed are important determinants of soil acidity. Additional information on soil pH may be found in the Ohio Agronomy Guide, available for sale at. For example, legumes require pH levels of 6.2 or higher, but corn can be productive in soils with pH levels as low as 6.0. However, soil does not have to be neutral (pH 7.0) to maximize nutrient uptake or crop production. Low soil pH also limits the release of some nutrients from soil organic matter and reduces nitrogen fixation by legumes. Aluminum in soil solution binds with phosphorus (decreasing phosphorus availability to plants) and inhibits root growth and development (limiting nutrient uptake). High concentrations of hydrogen in soil solution (low soil pH) may cause the release of soluble aluminum from soil minerals. A pH value below 7.0 is considered acid and, depending upon the soil pH and the crop being grown, may require neutralization to raise the soil pH. Due to the way pH is calculated, the higher the hydrogen concentration, the lower pH becomes. PH is a measure of the hydrogen (H +) ion concentration in solution. Soil pH affects soil microbial activity and populations, many soil chemical reactions, and nutrient availability thus it is an important soil property to consider for maximum productivity. Soil pH is an important consideration when producing any crop, and soil pH should be the first soil consideration when attempting to grow a plant.
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