Graduate Thesis Or Dissertation
 

Liming requirement of selected Willamette Valley soils

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  • 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.
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