Influence of moisture availability on yield and quality of Trifolium species

The response to moisture availability by Trifolium species possessing different reproductive strategies was investigated to determine the implications of using moisture availability to manipulate plant growth and increase seed yield. White clover (Trifolium repens) (a self-incompatible perennial), T. occidentale (a self-fertile perennial) and ball clover T. nigrescens (a self-incompatible annual) were studied. T. repens and T. nigrescens were grown in a controlled environment and three levels of moisture availability were imposed; a control treatment maintained at field capacity and two treatments designed to reduce petiole extension rates to 60 and 30% of the control. Plants were hand pollinated, and at harvest seed yield components measured. Plants of T. occidentale were grown in deep soil bins in an open glasshouse under three moisture regimes which were watered to field capacity every two, four or six weeks. Plants were pollinated by indigenous pollinator species, harvested when ripe and seed yield components evaluated. Differences between species were observed in size and quality of the seed produced and in response to moisture availability. For T. repens, mean seed weight and incidence of hard seed increased as the level of moisture availability decreased while in T. occidentale there was a significant decrease in mean seed weight and hard seed content as moisture availability decreased. For T. nigrescens mean seed weight increased, but the hard seed content remained constant as moisture availability decreased.