|Abstract or Summary
- There are two major problems associated with soil acidity and
lime response investigations:
A. Determining how much lime (100% "available" CaCO₃ equivalent)
is required to raise a soil pH (or degree of acidity) from its
existing level to a specified level - presumably where need for
lime is eliminated.
B. Determining responses of different crops on different soils to
lime; and defining some chemical measurement of the soil that
will predict the response of a specified crop.
Investigations in this study were limited to the first problem.
Liming characteristics of 45 acid Willamette Valley soils, representing
the major agricultural soil associations, were determined by incubating
the soils with increments of CaCO₃. The lime required to
bring the soils to the specified pH levels of 6.8, 6.4 and 6.0 varied
widely within the respective pH levels. Relationships between soils,
however, as determined by the value of the incubation curve slope
(meq. of CaCO₃ /100g of soil required to raise soil pH by one unit),
were improved by grouping into related soils. Laboratory measurements
of other soil chemistry parameters were compared with
changes in pH to determine if a satisfactory quick laboratory procedure
could be developed to measure the incubation lime requirement
of soils with different chemical characteristics.
Measurements of soil pH were made by three different methods:
(1) in the supernatant of a 1:2 soil to water suspension; (2) in the
sedimented paste of the 1:2 soil to water suspension; and (3) in the
supernatant of a 1:2 soil to 1 N KCl suspension. Lime requirement
with a buffered solution was measured in limed and unlimed
soils by use of the SMP (Shoemaker, McLean, and Pratt) buffer
method. Soil samples treated with increments of lime were analyzed
for extractable Al and exchange acidity by titration and the unincubated
soils were analyzed for exchange acidity determined by subtracting
exchangeable bases from CEC measured at pH 7. 0 and pH 6. 0.
Results of the correlation analyses showed that the SMP buffer
method should prove useful for predicting the incubation lime requirement.
Correlation coefficients for these two values were .89, .90
and 86, respectively, to reach pH levels of 6.8, 6.4 and 6.0. Soil
pH measurements, extractable Al, and exchange acidity determinations
did not provide as good a basis for determining incubation lime requirements,
Regression equations were calculated for the SMP
buffer/incubation lime requirement relationships.
The purpose of this study was to identify the changes in soil
chemical measurements that take place with application of lime. No
attempt was made to determine whether a crop might respond to an
application of lime on an acid soil. The assumption was made that
yield could be related to specific pH or soil acidity levels that could
be measured in the laboratory. Therefore, the problem was approached
by studying procedures that might determine the application of lime
required to reach a specified pH or soil acidity measurement. It
anticipated that field trials for evaluating lime response will be
carried out in the future to evaluate the usefulness of the SMP buffer
method which showed promise in this regard.