The contribution of a temporary watertable to surface soil water content and the establishment of surface sown seeds

Abstract

A temporary watertable was established in large undisturbed cores of a podzolic (duplex) soil in a glasshouse. The upward flow of water from the watertable to the soil surface through a 7 d drying cycle was assessed by measuring soil water content and matric potential, and the rate of evaporation from the soil surface (by weighing). Evaporation from the soil surface (Ea) closely followed evaporation from a free water surface (Eo), with little change in surface water potential or content until the watertable was depleted. This indicated that soil evaporation was balanced by the upward flux from the watertable, at rates up to 0.37 mm/h. Surface water potential was maintained above - 0.04 MPa for 7 d, and 12% of ryegrass seeds established themselves on the bare soil surface. When the A horizon was wet to field capacity but no watertable was established, Ea was much less than Eo especially in periods of high evaporation. Also, the soil surface dried to below - 0.04 MPa within the first day and no seeds germinated. It appears that sowing on sites with temporary watertables could assist germination and establishment after aerial sowing.