THE WEED FLORA OF CHEMICALLY‐RENEWED LOWLAND SWARDS

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Abstract
The viable‐seed content of soils under grass swards was investigated in relation to the potential weed flora which may occur in chemically‐renewed swards. The viable‐seed populations in the top 6 in. of the soils ranged from 46 million per acre for a 1‐year ryegrass ley to 1·7 million in an old permanent pasture. On the limited evidence available, there appears to be no close correlation between the broad‐leaved weed species present in the original pasture, the viable seeds in the soil, or the volunteer species in the new sward. Large populations of viable seeds of indigenous grass species occurred in most swards, while there was an almost complete lack of seeds of cultivated grasses. The effect of surface cultivation following the application of paraquat to a grass sward is to stimulate the dormant weed seeds in the upper layers of the soil to germinate. If these layers were left undisturbed a relatively weed‐free environment would eventually be achieved.

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