Molybdenum adsorption behavior was investigated on various crystalline and x-ray amorphous Al and Fe oxide minerals, clay minerals, CaC@, and arid-zone calcareous and noncalcareous s soils. Molybdenum adsorption on botb Al and Fe oxides exhibited a maximum at low pH extending to about pH 4 to 5. Above pH 5 adsorption decreased rapidly, with little adsorption occurring above pH 8. Molybdenum adsorption was higher for the oxide minerals having higher specific surface area and lower crystallinity. Molybdenum adsorption on the clay minerals exhibited a peak near pH 3 and then decreased rapidly with increasing pH until adsorption was virtually zero near pH 7. The magnitude of MO adsorption on clays increased in the order: kaolinite < illite < montmorillonite. Shifts in point of zero charge were observed on Al and Fe oxides and kaolinite following M O adsorption, indicating an inner-sphere adsorption mechanism for MO on these surfaces. Molybdenum adsorption behavior on three arid-zone noncalcareous soils resembled that on clays, exhibiting a peak near pH 3 to 4 and decreasing with increasing pH up to pH 7. This behavior is expected since the oxide content of these soils is low. Molybdenum adsorption on calcite and two calcareous arid-zone soils was low, indicating that CaCOJ is not a significant sink for MO in soils.

No abstract

The total and organic phosphorus were determined in five virgin‐like loess‐derived soil profiles occurring along a traverse from southwestern Iowa to northern Missouri. The soils studied were representatives of the Prairie (Brunizem), Wiesenboden, and Planosol great soil groups. The time of soil weathering was assumed to have been the major soil formation variable affecting the soils investigated. The degree of soil profile development in southwestern Iowa had been found previously to increase maximally in a southeasternly direction from the major source of loessial material at the Missouri River. The total phosphorus was found to decrease in the profiles along the traverse in relation to the degree of profile development, and the vertical distribution was found to vary in a systematic manner also. The action of soil weathering was found to have reduced the amount of phosphorus in the A horizons of the soils in relation to the amount found in the C horizons. The phosphorus measured on the B horizons was less than in the A or C horizons and decreased along the traverse to a minimum in the Haig profile (maximal Wiesenboden) and then increased slightly in the Planosol soils. The organic phosphorus was found to decrease also in relation to the degree of soil profile development along the traverse and to decline vertically in the profiles at a progressively greater rate with each succeeding more strongly developed profile. The data indicate a definite relationship between the amount and distribution of phosphorus and the stage of soil development exhibited in each of the profiles studied.

Self‐diffusion coefficients of 32P (D) were measured in four soils: Miller clay, Norwood loam, and two textural intergrades of these two soils. Clay percentages of the soils were: Norwood, 12.5; Intergrade I, 25.0; Intergrade II, 36.0; and Miller, 59.0. The P rates used were 0, 25, 50, and 100 ppm. The moisture levels were 35, 60, and 100% of the water content between ⅓ and 15 bars tension. The D values averaged over all clay and P levels, increased from 10.25 × 10‐10 to 27.76 × 10‐10 cm2/sec as the water content increased from 35 to 100% of the available moisture. The average D value increased from 5.05 × 10‐10 for the Norwood to 26.59 × 10‐10 cm2/sec for the Miller soil. Likewise, D values increased with increasing rates of added P for all soils. The data indicated reduction in available water has less effect on diffusion rates of P in clay soils than in the lighter‐textured soils. It follows that in order to maintain a given rate of diffusion in a soil, as water content decreases, the amount of added P must be increased.

No abstract