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Copyright 2005, Board of Trustees, University
&c AGRICULTURAL RESEARCH & EDUCATION CENTER
IFAS, University of Florida
/Iradenton AREC Research Report GC1976-14
SPEED OF REACTION OF FINELY GROUND DOLOMITIC LIMESTONE
S. S. Woltz
As the methods of culture of plants become more varied and complex, it becomes
necessary to improve the control and reliability of one of the simpler operations,
namely, liming soil or plant growth media. This report presents information on the
potential rate of reaction of a common liming material, finely ground agricultural
dolomitic limestone, commonly referred to as dolomite. A number of laboratory exper-
iments were performed in this connection using a single soil, virgin Myakka fine sand,
pHl 4.2. The experiment described below characterizes the action of dolomite mixed
with an acid soil.
A sample of finely ground agricultural dolomite was fractionated into four par-
ticle size ranges. Three of these, shown in Table 1, were used as well as the unfrac-
tionated dolomite in a time course experiment. Reagent grade calcium carbonate and
calcium hydroxide were used as chemical controls relative to the ultimate acid-neutra-
lizing capacity of the dolomite. Dolomite is reported to have a typical calcium car-
bonate equivalency of 92% (Breland, I. L. Lime in Florida's Agriculture. Fla. Agri.
Exp. Sta. Cir. S-155, 1964).
Soil was prepared by screening and air-drying in the greenhouse. Dolomite was
dried in a forced-air oven at 700C prior to screening. One kilogr m of soil and 1.5
grams of liming material were mixed very thoroughly by shaking in a clostspolyethyl-
ene bag. One hundred fifty ml of water was added and mixed-by keading the bag. /Bags
were then left open to the atmosphere by rolling down the tops. -Hater was added as
required to maintain a good moisture level for reaction, at or slightly above field
capacity. Small samples were removed at time intervals of 1, 2, 4 and 'days'for pH
determination. The results of pH measurements at time intervals from zero time are
shown in Table 1.
Table 1. Effect of various liming materials on soil pH of
virgin Myakka fine sand, initial pH 4.2.
Days after treatment
Lime amendment* 1 2 4 8
Dolomite, regular** 5.6 5.8 6.0 6.5
Dolomite, very fine 6.4 6.6 6.9 7.0
Dolomite, fine 5.0 5.3 5.5 6.1
Dolomite, medium 4.7 4.8 4.8 5.0
Calcium carbonate***, reagent 6.9 7.0 7.1 7.2
Calcium hydroxide, reagent 8.4 8.5 8.4 8.4
*1.5 gram mixed in 1 kilogram soil, equal to 3000 pounds/acre.
**Dolomite screen size: % of regular dolomite
Very fine through 200 mesh 77
Fine through 100 mesh held on 200 19
Medium through 60 mesh held on 100 3
Coarse held on 60 mesh 1
(Screen sizes used in Table 1)
***Powder, extremely fine particle size
Dolomite, a liming material generally recognized as slower acting, adjusted
the soil pH upward very rapidly as shown in Table 1. The pH reached a level of
6.5 in 8 days. The reason for this rapid reaction are (1) small particle size of
test material, (2) thorough mixing, made possible by having both soil and dolomite
dry prior to mixing, and (3) maintenance of soil moisture at a level adequate for
the support of chemical reactions. Wet or caked liming material is very ineffective
because of the adherence of particles into lumps. A granule of cohesive material is
not significantly better than an unground particle of the same size because such
granules will not be distributed any better than solid particles in the soil (Volk,
G. M. and N. Gammon, Jr. Soil Reaction (pH). Agr. Exp. Sta. Circ. S-39, 1951).
The screen size of dolomite affected the reaction velocity in the usual manner,
namely, the finer the particle size the faster the reaction occurred. Chemically
pure (CP), powdered calcium carbonate and hydroxide reacted very rapidly. These
chemicals were included as standards to determine the acidity reserve of the soil.
The principal observation to be made from Table 1 is that ordinary liming
materials can react very rapidly under conditions of intimate mixture with the soil
and maintenance of adequate soil moisture. These short-term observations will sup-
plement the abundant long-term observations which have been compiled in soils and
horticultural literature. Predictability in liming results requires that both lime
and soil be dry enough to be intimately mixed. Moisture must then be supplied dur-
ing the reaction period if rainfall does not occur. Starting from the optimum con-
ditions listed here and going to various conditions encountered in agricultural
practice, one may estimate in a gross manner the likelihood of slow, moderate, or
rapid pH- adjustment. In this connection, Volk and Gammon (Circular S-39, Fla. Agri.
Expt. Sta., 1951) described the results to be expected from coarsely ground lime-
stone as follows: "The percentage of ground calcic or dolcr-itLc limestone passing
a 60-mesh sieve is a fair measure of the relative rate with which a material will
react when thoroughly incorporated in the soil.... The portion of a material
retained on a 20-mesh sieve is so slow in reaction that it will hardly justify the
cost of handling...."