Soil surface moisture measurement and its influence on the establishment of three oversown legume species

Abstract

SUMMARYSoil surface moisture is a dominant factor influencing the establishment of surface sown seed, but its measurement is difficult. A cobalt chloride (CoCl2) saturated paper strip (20×5 mm) technique was developed as a cheap but sensitive indicator of soil surface moisture. The influence of soil surface moisture on the seedling survival of three oversown legume species, subterranean clover (Trifolium subterraneum L. cv. Karridale), strawberry clover (T.fragiferum L. cv. Grasslands Onward) and Caucasian clover (T. ambiguum Bieb. cv. Monaro) was investigated in a glasshouse and a field experiment at Palmerston North, New Zealand, between 1 October and 30 November 1993. Intact sods were sprayed with glyphosate, placed in plastic trays (420×300×50 mm) and transferred to the glasshouse or field. Three soil surface moisture treatments were imposed in the glasshouse. In the field trial, the plastic trays were buried flush with the soil surface in contact with the subsoil and exposed to natural wind and rainfall. Bare seed was oversown in a 20 × 20 mm grid and then pushed into the soil with a roller studded with metal rods to simulate treading by sheep. The low soil surface moisture treatment and the field trial had the lowest seedling survival. The main cause for this was low surface moisture caused by wind, which hindered radicle entry into the soil. Subterranean clover was less susceptible to low surface moisture and had better net seedling survival in all the treatments than the other two legume species.