Tuesday, August 16, 2022

Liming Purpose And Options

Peanuts are known to be good scavengers of many nutrients in the soil. However, calcium, one of the most critical elements for good pod yield, must be applied so it can be absorbed through the hull of developing pods. 

Lime or gypsum are the two sources of calcium used in peanut. If an increase in pH is needed, a lime source can be surface applied months in advance for gradual breakdown into the soil solution. Lime should be added if the soil pH is below 5.8, with the target pH being 6.2–6.5. 

If lime is needed, both dolomitic or calcitic lime can be used. Both types increase pH and reduce soil acidity. Calcitic lime is derived from deposits of primarily calcium carbonate. If magnesium is needed, a dolomitic lime can be selected, because it has higher concentrations of magnesium, as it is sourced from deposits containing both calcium carbonate and magnesium carbonate. 

Lime Needs Time

Lime needs time to solubilize, so applications must be made prior to planting for reactions to occur in the soil and for optimal plant uptake by the time plants need it during reproduction. In deep-turned soil, applying lime beforehand will enhance distribution and raise pH faster in the root zone. If a lime source is surface applied after planting peanut, it will not have time to raise the pH or be fully available for calcium uptake by pods.

The two key factors used to compare materials used to raise soil pH are calcium carbonate equivalent and particle size. 

The calcium carbonate equivalent standard is set at 100 (pure calcite). In comparison, common ag lime averages approximately 75% to 100% of pure calcite (calcium carbonate equivalent = 75 to 100). If your product has a calcium carbonate equivalent of 50, you will need to apply twice as much  to meet your soil report liming recommendation. 

Table 1 provides calcium carbonate equivalent estimates of common liming materials that may be available in your area. Use this information as a guide but request the specific calcium carbonate equivalent, particularly of alternative liming materials, from supply dealers for final consideration and application calculations.

Particle Size Matters

The particle size distribution is also important. Liming sources with finer particles will react with moisture in the soil and affect soil pH more quickly. Conversely, products with larger-sized particles will take longer to affect soil pH. Particle size is measured by passing the product through a mesh screen. Bigger numbers correspond to finer mesh and smaller particles. For a faster reaction time, you want a greater proportion of particles to pass through 50 mesh (50 openings per inch). In comparison, particles larger than 20 mesh (0.03 inch diameter) will likely provide little to no liming ability. 

Combining the attributes of calcium carbonate equivalent and particle size is called the effective calcium carbonate equivalent or relative neutralizing value. If available, this value is the best estimate of liming power for your field. Generally, many states use a wet sieving method to determine percent of material that passes through three or more different sieve sizes to help determine effective calcium carbonate equivalent. In Florida, lime material suppliers must provide calcium carbonate equivalent and list the required tonnage needed to be equal to 1 ton of standard liming material, which is the equivalent application rate already determined for you. 

Standard Definitions

Other minimum guarantees include a maximum of 15% moisture, and a “standard liming material” must have a calcium carbonate equivalent of at least 90%. Other liming materials not labeled as “standard” must have at least 75% calcium carbonate equivalent. A calcitic liming material must be comprised of at least 70% calcium carbonate and the remaining calcium carbonate equivalent will be from magnesium carbonate. In dolomitic liming material, at least 30% will be magnesium carbonate and the remainder calcitic carbonate. 

Pelletized lime tends to be finely ground. A greater proportion of the pelleted material passed through 100 mesh (prior to being pelletized). Florida regulations require the label to state how much of this material is equivalent to 1 ton of “standard liming material.” These materials can typically be applied at a rate approximately 10% to 20% less than standard liming materials, or perhaps 30% to 40% less than non-standard liming materials that have a minimum calcium carbonate equivalent of 75%. However, the finer ground the liming material, the less longevity it may have in the field. PG

Article by Cheryl Mackowiak, University of Florida/Institute of Food and Agricultural Sciences soil scientist, North Florida Research and Education Center in Quincy.

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