Phosphate fractions and their relation to the weathering and genesis of some soils of the Texas high plains

Abstract

This investigation was undertaken to determine the weathering status and genetic relationship of the Pullman, Amarillo, and Brownfield soils of the Texas High Plains. These are extensive soils of the area and are of considerable agricultural importance since they occur in the most extensively irrigated region in Texas. The Ruston soils of East Texas were included to provide a relative measure of the weathering intensity. Laboratory analyses included: (a) determination of total soil phosphorus; (b) fractionation of the inorganic phosphates into dicalcium, calcium, aluminum, iron, reductant-soluble, and occluded iron-aluminum phosphate fractions; (c) determination of available phosphates by the Olsen and Texas methods; (d) determination of the titanium and zirconium content of the 0.05-0.25 mm sand fraction; and (e) determination of the very fine/fine sand ratios. The Pullman, Amarillo, and Brownfield soils have formed in the aeolian mantle of the Llano Estacado physiographic unit. The sediments of this mantle were calcareous as indicated by the accumulation of calcium carbonate in the soil profile and the soil reactions. Mineralogical and heavy mineral data show that the soils consist of the same types of materials with marked differences in the amounts of these materials. These differences are believed to have occurred from the selective deposition of the aeolian parent material which determined the relative amounts of quarts and mica at a given location. The Ti0₂/Zr0₂^ ratios indicate that | the sediments were complex and heterogeneous although the sand fraction data indicate that the sediments of individual profiles were uniquely distinct with the exception of one Amarillo soil..