Soil Water Potential Requirement for Germination of Winter Wheat

In semi-arid climates, seed is often sown into soil with inadequate water for rapid germination. Distinguishing between adequate and marginal water can be difficult. Planting decisions become increasingly complicated when one considers possible differences between cultivars. This study was designed to measure the soil water potential limits for rapid, adequate, and marginal germination of winter wheat (Triticum aestivum L.). Laboratory data showed that germination was rapid (3 to 4 d) in soil at water potentials above -1.1 MPa and slower (4 to 5 d) at water potentials that ranged from -1.1 to -1.6 MPa. Below -1.6 MPa, less than half of the experimental units achieved the cutoff criteria of 75% germination with 5-mm radical length within 25 d. Six cultivars varied in time to germination by an average of 0.34 d, and two randomly selected seed lots of each cultivar differed by an average of 0.20 d. We conclude that variation between seed lots may be as important as variation between cultivars when looking for seed with superior germination under marginal soil water contents.