The shoot:root ratio of Italian ryegrass and perennial ryegrass cv. in the vegetative phase was constant under constant conditions. With intermittent N supply, root mass and shoot:root ratio of ryegrass in monoculture varied widely. Both relatively and absolutely, root mass was larger than with constant N supply. Short periods of low N were sufficient for a marked increase in root growth. Under constant environmental conditions root mass was closely related to defoliation frequency.

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... genetic variation in root mass existed between perennial ryegrass clones. Differences were largest under conditions of max. root growth. Root mass was positively related to competitive ability. (Abstract retrieved from CAB Abstracts by CABI's permission)