COMPARATIVE GROWTH OF WHITE CLOVER SOWN INTO POTS OF SOIL FROM OLD PASTURES AND ADJACENT ROADSIDES

It is often claimed that improved pastures grow better in the early years after initial establishment than after many years of fertilization and grazing. A pot experiment was conducted to compare the dry matter production of white clover and perennial ryegrass when sown into soil from old established pastures and into soil taken from adjacent roadsides which had not previously been cultivated, fertilized, sown or grazed. On 8 out of 10 sites, white clover growth was consistently poorer when sown into the paddock soil than into the roadside soil. The average growth on paddock soil from these 8 sites was only 61% that of growth on the roadside soils. With perennial ryegrass there was no similar depression; in fact, the overall average growth of grass on the paddock soils was 121% that on the roadside soils. The explanation for this difference in growth of clover on the two soil types was apparently not due to any difference in the N status of the clover plants, as at no harvest was this difference significantly reduced when N fertilizer was regularly applied to the clover. The economic importance of these findings depends on confirmation of the results in the field. Possible, but untested, explanations may lie in different levels of soil-borne pests and diseases, or a residual allelopathic effect of improved pasture species on the growth of clover on the old pasture soil.