The effects of sand type and fine particle amendments on the emergence and growth of subterranean clover (Trifolium subterraneun L.) with particular reference to water relations

Abstract

Twelve types of sandy soil exhibited considerable differences in ability to promote emergence? of subterranean clover when compared under suboptimal soil water conditions. These differences resulted from interactions between soil water relations, mechanical impedance, and aeration. Water requirements for satisfactory emergence of subterranean clover in a coarse sand were studied in the laboratory. Highest emergence was achieved when a water content of 10% by weight (–10 cm water potential) was maintained for at least 4 days. Very little emergence occurred when the water content was maintained at 2% by weight ( –120 cm water potential). A sustained water content of about 10% for 4 days was infrequently achieved in the field under natural rainfall conditions. Initial establishment and subsequent maintenance of subterranean clover on coarse sands in the field can be critically limited by the effects of poor soil water relations on emergence. Incorporation of 2.5% by weight of three fine particle amendments in the topsoil produced spectacular improvements in emergence and establishment. Fly ash was superior to clay, which in turn was superior to finely ground silica. This was due in part to beneficial effects on nodulation and growth. Incorporation of fine particle material in the soil layer below the seed zone required less material to produce the same response as uniform mixing throughout the topsoil.