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Back | Quarterly Report | Iowa Dept. of Agriculture Aglime Research Soil Acidity Limits Crop Yields The soil in many Iowa fields is becoming more acid. The problem has grown increasingly worse in recent years. It now threatens the ability of many farmers to sustain their current crop yield levels. "Soil acidity is robbing income from farmers in many areas of Iowa," warns Iowa State University extension agronomist, Regis Voss. Soil pH Soil pH is a measure of the acidity or alkalinity of the soil. The degree of acidity or alkalinity is determined by measuring the concentration of the hydrogen (H+) ions in the soil solution. This is expressed in terms of a scale with a range of 0 to 14. A pH value of less than 7.0 is considered acid and a soil with a pH greater than 7.0 alkaline. At a pH level below 5.0, elements such as aluminum, manganese, and iron become more soluble in the soil solution. These levels could be considered toxic to the plant.
 Determining Soil
pHIf lime is needed, spend your first dollars on Aglime. Liming will make more of the nitrogen, phosphorus and potash already present in the soil more available for plants. The pH is dynamic. In order to determine what it is, a soil sample of the tillage depth (0-6 inches) should be sent to a soil testing laboratory to be analyzed by trained professionals every 2 to 4 years.  The Role of Lime
Calcium and Magnesium In Iowa, Aglime is sold on its neutralizing ability (ECCE), not on its percentage of calcium or magnesium. Top agronomists from Iowa State University, University of Wisconsin, and the University of Illinois advise that it is the carbonate content of both calcium and magnesium that raises the soil pH. Calcium and magnesium are benign carriers. The most common liming materials include calcite (CaCO3), and dolomite (CaCO3MgCO3). The speed of the reaction is dependent upon contact of the lime with the soil. Smaller particle sized liming materials react faster to neutralize the soil and are more effective than larger particles. For every pound of ammonia nitrogen fertilizer applied, 3.6 pounds of lime are needed to needed to neutralize the acidity produced by nitrification. Benefits of Liming Aluminum and Manganese Toxicity The primary reason low pH reduces crop yields, is because the lower the soil pH, the more available aluminum and manganese become. Even at low concentrations, aluminum and manganese ions can be very toxic to most crops. As a result of low soil pH, aluminum toxicity is a major factor in limiting crop production throughout Iowa. Liming the soil reduces the solubility of both aluminum and manganese removing them from the soil solution. Nutrient Availability  The availability of most nutrients is
greatest between a soil pH of 5.6 to 6.5. The soil pH of 6.2 to 7.0 is
considered best for crop production. Liming improves the physical condition of the soil, resulting in greater root proliferation and nutrient uptake. Liming an acid soil to a proper soil pH improves the fertility and physical characteristics of the soil. Aglime increases microbial activity, effectiveness of certain herbicides, and ultimately crop production. It also raises the amount of calcium available for the plant to use in cell development. Many soil experts feel this added calcium availability often increases crop yield, even when the original soil pH tested near neutral. A growing plant removes calcium and magnesium from the soil, which lowers the soil pH. In the process of nutrient uptake, the plant releases H+ ions into the soil, increasing the soil acidity. Plant decomposition also contributes to the overall soil acidity.
Lime and No Till On an acid soil, aglime should be incorporated to adjust the soil pH to the desired level in the entire plow layer before no-till crop production is initiated. Studies show that surface applications of lime will rapidly change the pH of surface soil. They also indicate that even shallow pH improvement could affect herbicide activity and nutrient availability. Recent Pennsylvania State University studies indicate - "On no till fields it may take up to 9 years to bring the pH of the top 6" to desired levels are attained, they are easy to maintain with no incorporation." This study also indicates surface liming approximately every three years, based on a regular soil testing program, should be adequate for no-till systems. Balanced Fertility Maintaining an optimum nutrient balance can be accomplished by soil testing on a regular basis and applying lime, nitrogen, phosphorus, potassium, sulfur and micronutrients as required. Increased nutrient availability and crop production result when lime is included as part of a Total Nutrient Management Program. Aglime| Members | Related Links | ILPA Email | Limestone Handbook | What's New | Home ILPA
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