A wet soil surface will lose water at a rate approaching evaporation from an open pan. A maximum air temperature of 40 F has a pan evaporation of 0.2 inches, while an air temp of 78 F has a pan evaporation of 0.4 inches of water per day. It reduces to .02-.05 inches per day over 2 to 3 days when a dry layer thick enough to form a protective cover develops. The dry soil depth necessary to retard water loss will vary with surface conditions. Surface roughness and soil color also affect seedbed water loss.
Dark soils absorb heat, increasing rates of loss.
Proper packer-wheel setting is achieved through trial and error. As a guide, packer-wheel setting is about right when soil density above and below the seed are indistinguishable. Seeding too rapidly - as seedbeeds dry, equipment performs differently, usually through loss of seeding depth control. Higher speed aggravates the problem, especially with spring-loaded double disc drills, which have a tendency to bounce and seed shallowly across hard spots. The symposium will focus on progress in disease research as well as disease-related marketing problems.