The objectives of this investigation were to (1) segregate the forms of soil acidity in certain Virginia soils and to study each form Independently, (2) to develop techniques to more accurately define the components of soil acidity, and (3) to relate forms of soil acidity to mineralogical and chemical properties and genesis of the soils studied. Three soils, Mayodan, Creedmore and Whitestore, developed from Triassic parent material in Chesterfield County, Virginia, were selected for the study. The high base unsaturation is responsible for the release of Al from the clay and its accumulation in the subsoils. The chemical data show that exchangeable Al is the predominant source of acidity. The mineralogy of these soils is quite similar. The predominant clay minerals present are kaolinite and vermiculite. From the acidity standpoint, the surface soils, compared to the subsoils, have better developed hydroxy-Al interlayers in the vermiculite. In the subsoils of the three soils the hydroxy-Al interlayer development is in this order: Mayodan>Creedmore> Whitestore, the same sequence as the drainage (decreasing). The main reason given for these differences in interlayer development is the frequency of wetting and drying. The ranges of soil acidity include H₃O+ (first range), Al³⁺ (second range) and positively charged hydroxy-Al groups third range). The potentiometric titration of the soils in <i>N</i> KCl do not show significant inflections for the third buffer range. Variations in the rate of titration and in temperature did not seem to influence the inflection for the third buffer range. The potentiometric and conductimetric titrations in H₂O, after the removal of exchange acidity and free-salt, give distinct inflections for the third buffer range. The conductimetric method for the determination of third buffer range in soils, as employed in this investigation, is recommended. The extraction studies with salt solutions and the potentiometric titrations of Al-saturated vermiculite show that only part of exchangeable Al is extracted with salt treatments and the rest is either hydrolyzed or trapped. The hydrolyzed Al is titratable, whereas the trapped Al is chemically inactive. MgCl₂ was more effective than KCl as an extractant. This is probably due to the greater hydrated radius and the higher valence of the Mg-ions. The smaller K ion causes collapse of the vermiculite and trapping of Al in the interlayer space. The results show that the use of KCl in soil titration is not recommended because of its effect on Al-hydrolysis, the competition of added Cl^- ions with OH^- ions and the trapping effect during K-fixation when vermiculite is present. / Ph. D.

An investigation of the pH, organic matter content, and cation exchange properties of the soil of the 26-year-old rotation and continuously cropped plots at Blacksburg, Virginia was carried out. Individual soil samples were taken of the eight sub-plots which represent each plot. After the chemical work had been completed, the data obtained were analyzed statistically. As a result of this investigation, the following conclusions are considered worthy of mention: Fertilizer and cropping practices which tended to increase crop yields also tended to increase soil organic matter and cation exchange capacity. There was a significant, positive correlation between organic matter content and cation exchange capacity of the soil. The organic fraction seemed to be of greater importance than the mineral fraction in contributing to the cation exchange capacity of this soil. Superphosphate, rock phosphate, muriate of potash and farm manure had or no effect on soil reaction. Ammonium sulphate caused a reduction of the pH and exchangeable calcium and magnesium and an increase in exchangeable hydrogen. The application of this fertilizer decreased exchangeable calcium but had no influence on the pH. Of the total potassium applied as muriate of potash, an average of 15 percent remained as exchangeable potassium in the upper six inches of soil. Where farm manure was applied, exchangeable calcium, magnesium, potassium, and cation exchange capacity were increased significantly. Examination of the samples and crop yield data from the check plots indicated considerable soil variation. / Master of Science