Why Lime Effective Calcium Carbonate (ECC) Matters
LIME CAN IMPROVE ACID SOILS FOR OPTIMUM WHEAT PRODUCTION
Dorivar Ruiz Diaz, PhD
Assistant Professor, Kansas State University Dept of Agronomy
Soil Fertility and Nutrient Management
Problems of low soil pH are common throughout central and south central Kansas. Well-drained, productive soils under good management usually become acidic over time as natural result of high crop production. This problem typically starts in sandier soils, and is exacerbated by high rates of nitrogen (N) fertilizer application over the years; making long-term continuous wheat production in central and south central Kansas especially vulnerable to this problem.
Strongly acidic soils may present several problems for wheat production. These include aluminum toxicity and in some cases manganese toxicity, as well as deficiencies of phosphorus, calcium, magnesium, and molybdenum. These problems caused by acid soils are difficult to separate one from another and are often simply referred to as the acid soil “headache.”
Aluminum toxicity is the most serious problem that can be associated with acid soils. Typical symptoms of aluminum toxicity include thin stands, poor plant vigor, and purpling. High concentrations of aluminum will reduce development of the roots, giving them a short stubby appearance. The roots will often have a brownish color.
In general terms, aluminum toxicity will reduce yield potential of wheat when soil pH levels get below 5.2 to 5.5 and KCl-extractable (free aluminum) levels are greater than 25 parts per million (ppm). If aluminum levels are not high, pH levels in this range are not as much of a problem for wheat. When soil pH levels are 5.0 or less, yields start dropping off rapidly in most cases.
Where acid soils are causing reduction in wheat production, plant growth and yield can be significantly improved by liming the soils and raising the pH to an optimum range.
What kind of yield increases can you expect? Several studies in Kansas have shown significant increase in yield as well as test weight when liming acid soils (Fig 1 and Table 1). In some cases yield can easily double depending on the severity of the problem.
It can be expensive to apply the full recommended rate of lime to soils. The yield increases from an application of the full rate of lime are likely to hold up for up to 8 years or more. But the initial cost can be quite high. Lime is a long-term investment that many producers are reluctant to make for several reasons. Should producers consider applying a lower rate of lime than what is recommended by the K-State soil testing laboratory?
If the cropping system consists of some combination of wheat, grain sorghum, corn, or sunflowers, without a legume in the rotation, then it's not critical to use the full recommended rate of lime. With these crops, which can tolerate somewhat lower pH levels than soybeans and alfalfa, producers may realize some benefit by applying less-than-recommended rates of lime as long as they are willing to make more frequent applications. If soybeans or alfalfa will be grown on the field in question, and if the pH level is less than 6.0, then the full rate of lime should be applied.
Table 1 below shows the effect of a lower than-recommended rate on wheat yield and test weight. The half-rate increased yield and test weight nearly as much as the full rate in this case. However, producers should be aware that if they use lower-than-recommended rates of lime, they will need to make more frequent applications.
What type of lime is best to apply? All lime materials must guarantee their ECC content and are subject to inspection by the Kansas Department of Agriculture. The purity of the lime material relative to pure calcium carbonate and fineness of crushing are the two factors used in determination of the Effective Calcium Carbonate (ECC) content. Lime can be from various sources and with different qualities. Consecutively, to ensure a standardized unit of soil-acidity neutralizing potential, we use units of ECC.
The ECC is the result of the Calcium Carbonate Equivalence by the Fines Factor of the liming material (ECC= CCE × FF). The Calcium Carbonate Equivalence (CCE) relates to the purity of the material, and is defined as the acid neutralizing capacity, expressed as percent weight relative to pure calcium carbonate (CaCO3) determined in the lab. And the fines factor is established based on ranges in particle size.
Reports from the soil testing lab would generally provide lime recommendations in lbs of ECC/acre. Therefore, the producer needs to know the value of the local liming material in terms of ECC. A simple calculation is shown in Table 2.
With the example in Table 2, if the soil test result suggests an application rate of 3,000 lbs/acre ECC, then the producer will need to estimate the amount of actual lime to be applied (3,000/ 0.6 = 5,000 lbs/acre). Recommendations from the soil testing lab are for the 6-7 inch depth, and for a no-till system this rate should be reduced to 1/3 of the full rate (assuming 2-inch depth of incorporation).
Research has clearly shown that a pound of ECC from ag lime, pelletized lime, water treatment plant sludge, fluid lime, or other sources are equal in neutralizing soil acidity. All lime sources have a very limited solubility and must be incorporated and given time to react with the acidity in the soil to effect neutralization.
Therefore, when selecting a lime source the cost per pound of ECC should be a primary factor in source selection. Such factors as rate of reaction, uniformity of spreading, and availability should be considered, but the final pH change will hinge on the amount of ECC applied.
Other recommendations to increase yields in acid soils include the use of aluminum-tolerant wheat varieties and applying phosphate fertilizer with the seed to tie up aluminum and reduce toxicity. These management practices can certainly help to maintain yields and may be the best alternatives for some producers. However, there is only one long-term solution to low soil pH levels: liming.