Geographic variation in the reduction of hard seed content of Stylosanthes seeds in the tropics and subtropics of northern Australia

Abstract

The reduction of hard seed content at three sites-Katherine, Townsville and Narayen-was dominated by changes in soil temperature. The amount of soft seed formed was controlled by the number of days during which the maximum soil temperature rose above 50-55¦C, and these varied with both the site and the season. From these observations a predictive relationship was developed which related hard seed content of seed samples in the field to soil temperatures. Comparison of the sites with this relationship showed three distinct patterns of hard seed reduction, with the majority of soft seed being formed in the pre-wet season for the tropics and during the early summer months for the subtropics. The importance of the predictive relationship developed with the above data was discussed in terms of patterns of germination at the field sites used.