EFFECT OF STRENGTH, TILTH AND HETEROGENEITY OF THE SOIL SURFACE ON RADICLE‐ENTRY OF SURFACE‐SOWN SEEDS

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Abstract
Seeds of Medicago sativa, Trifolium subterraneum, Lolium perenne and Phalaris tuberosa were sown on different soil surfaces and the effects of strength, tilth and heterogeneity of the surface on the entry of the radicle into the soil were noted.On a level, finely structured soil surface prepared in the laboratory slight increases in soil strength markedly reduced percentage radicle‐entry. At constant soil strength, radicle‐entry was greater on coarse than on fine tilth; which helped to explain the higher percentage radicle‐entry on heterogeneous soil surfaces taken from the field compared with the level, finely structured surface, prepared in the laboratory despite the lower soil strength of the latter.As conditions for radicle‐entry hecame less favourable (stronger, smoother surface) the rate of radicle‐entry became slower and there was a greater use of radicle‐entry methods in which the radicle was more exposed to desiccation.The radicle‐entry ability of the four species declined in the order: perennial ryegrass < phalaris < lucerne and subterranean clover. Factors considered to account for the superior radicle‐entry of the grasses were better anchorage of the seedling, better angle of entry of the radicle and smaller radicle diameter.