A comparison of seedling emergence and early seedling growth from dry-sown natural and fluid-drilled pregerminated onion (Allium cepaL.) seeds in the field

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Abstract
The emergence of seedlings from natural ungerminated, fluid-drilled germinating and uniformly germinated seeds was studied in a range of changing environments in both irrigated and unirrigated crops. In general, seedlings from uniformly germinated seeds emerged before those from germinating seeds, and seedlings from both emerged before those from ungerminated seeds. This earlier emergence from germinated seeds led to larger seedlings at subsequent harvests. The timing of emergence was correlated with mean temperature in all seed treatments on irrigated plots, but only in the uniformly germinated seed treatment on unirrigated plots. Fluid-drilled germinating seeds produced consistently greater spreads of seedling emergence times than either the uniformly germinated or the ungerminated treatments over the whole range of environmental conditions. More seedlings emerged from uniformly germinated seeds than from ungerminated seeds particularly under more favourable conditions, whereas germinating seeds tended to produce more seedlings than ungerminated seeds under favourable conditions but fewer under poor seed-bed conditions. The percentage emergence was negatively correlated with mean temperature in the ungerminated and germinating seed treatments but not in the uniformly germinated seed treatment. However, percentage emergence from uniformly germinated seeds was correlated with initial soil moisture content. The results suggest that the major cause of pre-emergence seedling losses from germinated seeds was soil moisture stress which can be largely overcome by pre-sowing irrigation.