EFFECT OF GROWING RYEGRASS ON THE DISTRIBUTION OF ZINC IN SOIL POOLS

The distribution of zinc between soil pools was measured over 48 weeks in grassed and bare soils using selective extractants. Although changes in the extractable fractions of zinc occurred in all soils, they tended to be less in the bare soils. From weeks 18 to 48 the rate of uptake of zinc by ryegrass ranged from 3.4 to 106-mu-g Zn/week in the 5 soils studied. The CaCl2 - extractable Zn in the soil increased over the 48 weeks, while the amount of acetic acid-, EDTA-and oxalate - extractable Zn decreased. Superimposed on these changes was the effect of growing ryegrass. There was relatively more CaCl2-Zn, but less acetic acid-Zn and oxalate-Zn, in the grassed soil compared to the bare soil. There was no significant change over time in the difference in the EDTA-Zn pool between grassed and ungrassed soils. Comparison of zinc taken up by the ryegrass and zinc lost to soil, measured by oxalate extraction, suggested that selective extraction was not a good measure of zinc uptake by grass.