Dewan, Hari Chand2024-03-122024-03-121965https://hdl.handle.net/10919/118380The 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.170 leavesapplication/pdfenIn CopyrightLD5655.V856 1965.D482Soil acidity -- VirginiaDissertation