Soil labile of manganese, iron, and zinc as measured by plant uptake and DTPA equilibrium

Labile pools of Mn, Fe, and Zn were measured on soil samples having varying pH levels at both air-dry and field-moist conditions using DTPA. Labile pools of Mn and Fe varied with respect to both pH and soil moisture. The effects of soil moisture and pH on Zn labile pools were slight. Air-dry soil samples at three pH levels were labelled with carrier-free 54Mn, 59Fe, and 65Zn, and ladino clover (Trifolium repens) and tall fescue (Festuca elatior, var. Ky 31) were grown on each in a growth chamber. Uptake of the stable isotopes and radioisotopes was determined and the data were used to calculate soil labile pools of each element. Soil labile pools of Mn measured by ladino clover uptake were very similar to the values obtained from DTPA equilibration. Values for Fe labile pools were higher and generally in disagreement with DTPA-measured pools. Plant measured values for Zn varied depending on soil pH with respect to DTPA-measured pools. Tall fescue-measured soil labile pools of Mn, Fe, and Zn were calculated from uptake data of various combinations of cuttings. At a given pH, Mn labile pools calculated from any of the combinations were remarkably similar, but were lower than DTPA measured pools. Iron and zinc labile pools were erratic with respect to both soil pH and cutting used. Uptake data suggested that a single harvest of tall fescue at ground level after a 5-week growing period could be adequate to measure the soil labile pools of Mn, Fe, and Zn, especially if these elements were studied simultaneously