As you learned in the first YouTube Video in our educational series, pH plays a vital role in the health and nutrient availability of your soil. Please tune into our second video of the series to learn more about Buffer Index as it relates to your soil and appropriate lime application from our field representatives Joe Sisco and Jim Grilliot.

Buffer Index

The relationship between soil pH and buffer index is often misunderstood. Confusion between soil pH and buffer index often occurs, since the two measurements are printed on the soil test report side-by-side. Both are the same unit of numerical measure, and both have commonly shared the pH nomenclature in the past.

Soil pH is a measure of active acidity. The buffer index qualifies acidic soil pH by determining how much lime material to apply in order to attain the desired pH level. The buffer index measures how much reserve acidity is present. The buffer index is configured by adding a chemical solution of a known pH – called a buffer to the soil-distilled water solution after initial pH measurement is taken. The amount of change in pH after the addition of the buffer solution measures a given soil’s reserve acidity or buffering capacity. It can then be used to compute a lime rate needed to achieve desired pH levels. Cation Exchange Capacity is a relative guideline, which can help relate the influences of clay and organic matter on a soil’s buffering capacity and resulting lime recommendations.

This table illustrates the relationship among soil pH, buffer index, and soil type (CEC rating) and their collective influence on the lime recommendations.

Cation Exchange Capacity

Cation Exchange Capacity or (CEC) is a calculated value that estimates the soils ability to attract, retain, and exchange cation elements. In order for a plant to absorb nutrients, the nutrients must be dissolved. When nutrients are dissolved, they are in the form of “ions” hence cat (ION) exchange.

CEC is a very important soil property influencing soil structure stability, nutrient availability, soil pH and the soil’s reaction to fertilizers. Soils dominated by clay with variable surface charge are typically strongly weathered. Soil pH change can also be caused by natural processes such as decomposition of organic matter and leaching of cations. The lower the CEC of a soil, the faster the soil pH will decrease with time. Liming your soil to higher than pH 5 will maintain exchangeable plant nutrient cations.

Soils with low CEC are more likely to develop deficiencies in potassium, magnesium and other cations while high CEC soils are less susceptible to leaching of these cations. 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 soil but requires many years to take effect.

Lime Application

Lime is applied to soil to increase pH, or increase acidity, as grass likes to be on the acidic side. However over applying lime is just as detrimental as needing it and going without. It is the balance of pH that is at stake causing the soil to base or alkali. When the soil is too base or too acidic, it cannot grow beautifully green and healthy. Balancing the soil’s pH is paramount in establishing a healthy root system and green foliage. Lime is composed of ground limestone which contains the minerals calcium and magnesium.

As it relates to CEC, the higher the CEC, the larger the quantity of lime that must be added to increase the soil’s pH levels. Sandy soils need less lime than clay soils to increase the pH to desired levels. Liming is by far the most cost-effective solution to neutralize your soil.

Proper liming provides a number of benefits:

  • Plants develop healthier roots which enhances drought tolerance.
  • Lime is a source of calcium and magnesium.
  • Nutrient solubility is improved by higher pH increasing plant nutrient supply.
  • Increased soil CEC occurs, as well as reduced leaching of basic cations, particularly potassium.
  • Optimal pH allows the breakdown of some herbicides preventing damage to rotational crops.

Although limestone can be applied at any time, several factors should be considered when planning an application. Most importantly the length of time required for pH correction to take place. Crops with more sensitivity to low pH, such as forage legumes, should have pH corrected well in advance of seeding. Soil moisture is critical for the reaction of limestone with soil acidity, thus rainfall patterns can also be used as a guide for application timing. Soils should be sufficiently firm to support heavy equipment and minimize compaction. If subsoil pH is low, a long period will be required for limestone to effect change in the soil pH. Coarse limestone particles react more slowly and take several months to correct pH. Incorporation into the soil will provide faster reaction and pH adjustment.

Now that you know the crucial role of pH, buffer index, cation exchange capacity and lime application to improve your soil health and nutrient availability, get your soil tested by our experts at Midwest Labs by clicking on the following:

S3C with Recommendations

If you have additional questions on proper soil testing, please contact Midwest Labs at 402-334-7770 today.