19

 The gravel is a composite of four visually distinguishable classes

composed of goethite, gibbsite, kaolinite, and an unidentified mineral

containing Mn (Table 3-3). The porosity of the gravel ranges from 0.13

to 0.32 mL/mL, with a natural-composite sample porosity of 0.2 mL/mL.

 The moisture-release curve for the top 72 cm of soil is shown in

Fig. 3-1. The soil-water content exhibited no initial plateau at low

tension, thereby suggesting the presence of some very large pores that

are full when the soil is saturated, but which drain under relatively

low tensions. The soil lost nearly 0.2 mL of water per cm3 of soil

between saturation and 350-mbar tension (hypothetical field capacity).

It maintained 0.14 mL of water per cm3 of soil between 350-mbar and 15-

bar tension (hypothetical plant-available water).

 Phosphorus adsorption isotherms are presented in Fig. 3-2. The Ap

 horizon exhibits a strong affinity for P, and required nearly 500 ug P/g

 soil (750 kg P/ha to a depth of 15 cm) to support a solution

 concentration of 0.2 ug/mL. The gravel displayed a low affinity for P.

 Taxonomic Classification

 The Ap and Ac horizons constitute an umbric epipedon. The

 epipedon has weak, medium, subangular-blocky structure that breaks to

 moderate crumb. The color has a moist Munsell value and chroma darker

 than 3.5. The organic-carbon content is greater than 2.5%, and the

 depth of the epipedon is greater than 18 cm. Base saturation as

 measured by 1 M NH4OAc at pH 7 is less than 50%.

 The Btc, 2BCt and 2Cb horizons constitute an oxic horizon. This

 horizon is at least 30-cm thick. The cation-exchange capacity using

 NH4OAc (pH 7) is less than 16 cmol(+)/kg clay. There are no more than