Liming soils see Soil Acidity fact sheet. Several factors may restrict the release of nutrients to plants. Some groups promote the controversial idea of managing cation ratios, claiming ideal ratios for Ca:Mg or Ca:K. For plant nutrition, a more critical factor is whether the net amount of Ca or K in the soil is adequate for plant growth.
The addition of organic matter will increase the CEC of a soil but requires many years to take effect. Figure 1 illustrates how CEC can change with depth. The sum of the base cations provides an estimate of the CEC of each soil layer. The surface 10 cm has a CEC of 4. At 10 — 30 cm depth, the organic content of the sand is very low, hence the low CEC. The dominant clay in this soil is kaolinite so CEC values remain low.
Figure 1: Sandy duplex soil, with clay at 40 cm. Agronomy Fact Sheet Series With large quantities of fertilizers applied in a single application to sandy soils with low CEC, loss of nutrients is more likely to occur via leaching.
In contrast, these nutrients are much less susceptible to losses in clay soils. Crop production releases acidity into soil. Soil pH will decrease more due to crop production on low CEC soils. High CEC soils are generally well buffered such that pH changes much less from crop production.
Therefore, sandy soils low in CEC need to be limed more frequently but at lower rates of application than clay soils.
Higher lime rates are needed to reach an optimum pH on high CEC soils due to their greater abundance of acidic cations at a given pH.
Soil Test Handbook for Georgia. Kissel, D. Sonon Eds. Classes, Workshops, and Club Meetings UGA Extension offers a wealth of personalized services like workshops, classes, consultation, certifications, camps, and educator resources.
Find out what Extension has for you! Extension Changes Georgia University of Georgia Cooperative Extension programming improves people's lives and gets results. Our Impact. Extension Publications Circular Circular Figure 1.
Schematic diagram showing exchange of cations between the soil surfaces and the soil solution, and the movement of these cations from soil solution to roots rhizosphere for uptake. Figure 2. Influence of pH on the surface charge of soil and its components. Kissel Ph. Humus, the end product of decomposed organic matter, has the highest CEC value because organic matter colloids have large quantities of negative charges. Humus has a CEC two to five times greater than montmorillonite clay and up to 30 times greater than kaolinite clay, so is very important in improving soil fertility.
Clay has a great capacity to attract and hold cations because of its chemical structure. However, CEC varies according to the type of clay. It is highest in montmorillonite clay, found in chocolate soils and black puggy alluvials. It is lowest in heavily weathered kaolinite clay, found in krasnozem soils, and slightly higher in the less weathered illite clay.
Low CEC values can be improved by adding organic matter. Sand has no capacity to exchange cations because it has no electrical charge.
This means sandy soils such as podzolic topsoils have very low CEC, but this can be improved by adding organic matter. Aluminium is not present as a cation when soil pH CaCl2 is over 5 because it is precipitated out of the soil solution. It is only at pH CaCl2 levels below 5 that it may become available as a cation, and under 4. This is one reason why it is important to maintain pH levels at 5.
This shows up as dispersion or cloudiness in water.
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