TROPICAL PASTURE ESTABLISHMENT .6. TREATMENT OF SECA STYLO SEED TO REDUCE HARD SEED CONTENT

Two approaches were investigated for the reduction in hard seed conten t of Seca stylo (Stylosanthes scabra). One was to cause strophiole-bre aching through imposition of brief high temperatures by contact with a heated metal plate, and the other scarification of the testa by hamme r milling. Numerous combinations of metal temperature and duration of contact produced a range of levels of the heat dose applied (degree-se conds above 90-degrees-C). Response curves relating heat dose to the a mount of seed softening and killing were constructed. The similarity o f the softening and killing curves, coupled with inconsistency in resp onse between seed lots, explained unreliable results of treatment that were not materially improved by modifications such as prior wetting o r rapid cooling after heat treatment. Two causes of inconsistency were detected: a sharp fall in the mean critical heat dose for killing as seed moisture content rose; and apparently different insulative proper ties of upper and lower segment seed hulls. Heat treatment, besides ki lling some seeds, weakened survivors and further reduced the numbers o f seedlings emerging from soil. Despite its effectiveness in softening seed, it was judged to be too unreliable for practical use. Hammer mi lling, by comparison, was simple and effective. The extent of dehullin g could be controlled at about 50%, with germination of dehulled seeds raised to over 60%, and no effect on those remaining intact. Scarific ation is not a complete substitute for strophiole-breaching, but curre ntly there is no way to produce breached seed commercially other than by expensively suction-harvesting fallen, already weathered seed.