How to Determine Lime Requirements of Soils

The lime content required to raise the soil pH to the desired level is determined by measuring the buffer pH. While active acid refers to hydrogen ions in soil solution, “reserve acid” is used to describe hydrogen ions bound to cation exchange sites on clay particles in the soil. When all hydrogen ions in the soil solution are neutralized, replacement ions are released from these exchange sites, cushioning the change in soil pH. To effectively increase the pH of the soil, it is necessary to neutralize the active acid and a significant part of the reserve acid. Buffer pH is the process used to measure the amount of hydrogen ions bound to these exchange sites. We add soil to a buffer solution, with a known pH and an amount of acid needed to lower the pH, and measure the decrease in the pH of the solution. This value is then used to determine the amount of reserve acid, which is directly related to the amount of lime needed for neutralization. The amount of lime required to achieve a soil pH of 6.5 can be shown in Table 1 at the bottom of this sheet. The LBCEq value depends on the LBC30 of the soil, as already shown. Since LBC has ppm units, “2” is used to convert to lb/acre. Converting ppm to lbs/acre requires treating a soil depth of 6 inches. To convert from a depth of 6 inches to a depth of 8 inches typical of agronomic crops, the factor 8/6 is used.

The LBC looks at pure CaCO3, so 1.5 is used to determine an amount of agricultural lime that has lower purity. Examining all multiplication factors together results in a simplified equation, as shown below, used by the UGA soil testing laboratory. Soil acidity is a useful concept in terms of pH, aluminum toxicity, basic saturation of cation exchange capacity, cation ratios, lime requirements and nutrient availability that affect crop yield in tropical regions. Since the roots of fruit trees explore the same volume of soil for most of their lives, the uniform and deep incorporation of limestone at least 30 cm could provide a suitable root environment for the rapid establishment of plants and the efficient use of water and nutrients. Orchard planting offers a unique opportunity to integrate limestone deep into the soil to facilitate rooting, promote plant development and promote early fruit production. Before planting seedlings, it is recommended to apply evenly and incorporate 90 days before planting limestone of coarse particle size in the layers of 0-20 cm or 0-30 cm to increase the saturation of the soil base (V) to 65%. If the lime requirement exceeds 4 t/ha, it is recommended to apply half of the slice before ploughing, followed by a cross harrow, then apply the other half and repeat both operations. The use of alternative materials in the neutralization of acid mine tailings has been studied by some.

Overall, fluidized bed combustion residues were found to be less efficient than lime. This relative inefficiency was mainly attributed to differences in particle sizes between the two materials (Stout et al., 1982). Nevertheless, greenhouse studies conducted by Dick et al. (1994) found that dry, high-alkaline flue gas desulphurization by-products promote the regreening of acid residues when applied at levels that meet neutralization needs, with little potential for introduction of toxic elements into the leachate or food chain. The addition of 6% sewage sludge with the by-product of DGC created optimal conditions for plant growth. In Brazil, the demand for lime is determined on the basis of the Al, Ca and Mg contents of the soil and, for this purpose, the following equation is generally used: Although NMS (and thus SNS) can be measured by laboratory analyses of soil samples, in most cases the SNS index is determined by a “field assessment method” based on the previous crop. past use of fertilizers and organic manure, soil type and winter precipitation. The SNS index system is shown in Table 4.4.

Limestone is added to aquaculture ponds to increase pond bottom pH and overall alkalinity of pond water (Arce and Boyd 1975; Boyd, 1997; Boyd and Tucker, 1998). Low pond bottom pH is usually caused by replaceable aluminum (Boyd, 1995; Boyd and Tucker, 1998). Under these conditions, phosphorus reacts with aluminum to form insoluble aluminum phosphate. Pond soils can rapidly adsorb phosphorus from fertilizers, especially when granular fertilizer spread on the pond surface sinks to the bottom and phosphorus adsorption is similar in various soil types (Boyd and Musig, 1981). When limestone is added to attenuate the acidity of the pond bottom, the hydrogen ions produced during the hydrolysis of aluminum are neutralized by reaction with calcium carbonate, and the resulting calcium ion replaces the replaceable aluminum on the bottom. Soil pH increases when replaceable aluminum is replaced with calcium. The pond bottoms are limed to a final pH of 6.5-7. Analysis of pond bottom samples to determine lime requirements is beyond the scope of this chapter, but is described in detail by Boyd and Tucker (1998) and Silapajarn et al. (2005). In a broader sense, soil testing is any chemical or physical measurement performed on soil.

The main objective of the soil study is to measure the nutritional status of the soil and the demand for lime in order to provide recommendations for fertilizers and lime for profitable agriculture. Soil testing is an important tool in high-yield agriculture, but only gives the best results when used in conjunction with other good agricultural practices: calcification time is determined by measuring soil pH. pH is a measure of the amount of free hydrogen ions present in the soil solution. We call this part of the hydrogen ions an “active acid”. The lower the pH, the higher the concentration of hydrogen ions in solution. The tolerance of plants with low pH is different for some plant species. For example, most legumes (soybeans, alfalfa, etc.) are very intolerant to low pH and experience yield losses when soil pH drops below 6.0. On the other hand, most grass crops (corn, sorghum, wheat, etc.) are more tolerant at low pH and will produce quite well until the pH approaches 5.2.

For this reason, we recommend applying lime to legumes and other intolerant crops at a pH of 5.9 and below. For more tolerant crops such as grasses, we recommend lime at a pH of 5.2 and below. In order to adjust the soil pH to a desired or desired pH, it is necessary to know not only the current soil pH, but also the buffering capacity of the soil to withstand pH changes. Most soil testing laboratories give lime calibration recommendations based on the pH measured before and after the addition of a pH buffer solution. Research at the University of Georgia has developed a method to directly measure the amount of soil acid that must be neutralized by the application of lime. This property is called the lime buffering capacity (LBC) of the soil and is described below. Most often, agricultural limestone is the material used to neutralize the acidity of the soil. Agro-limestone is usually a mixture of calcite and dolomite that contains silica and other inert minerals. The Ca and Mg present in calcite and dolomite displace acid cations on soil particles, and the hydrolysis products are then neutralized by OH1– (Caruccio et al., 1988). where Al, Ca and Mg are in soil cmolc kg−1. In the state of São Paulo, soil texture and plant species are sometimes also taken into account for lime needs, and the above equation is written as follows: soil samples must be representative of the area in question. It is recommended to take at least one composite sample per 12–15 ha for lime and fertilizer assessments.

A representative soil sample consists of 15 to 20 subsamples from a uniform field with no major differences in slope, drainage or fertilizer history. Each of these listed factors, if modified, affects the number of samples and the unit of area from which the sample is obtained. Before planting new orchards, the best strategy for lime is to select limestone with a long residual effect in terms of particle size distribution and mineral composition. For example, Brazilian legislation allows the marketing of limestone with a low total relative neutralization force (NTP) of at least 45%, which contains coarse limestone particles (100% particles passing through a sieve with 2 mm openings) and has lasting effects. When calcareous material containing 45% PNRT is incorporated into acidic soil, 45% reacts within 90 days, leaving the remaining 55% for acid neutralization in years to come. The determination of limestone requires not only the TRNP, but also the mineral composition to achieve the appropriate cationic base saturation level.