TROPICAL PASTURE ESTABLISHMENT .5. IMPROVED HANDLING OF CHAFFY GRASS SEEDS - OPTIONS, OPPORTUNITIES AND VALUE

Many useful grasses have 'chaffy' seeds characterised by a range of ap pendages: awns, sterile spikelets, and surface hairs or bristles. En m asse, chaffy seeds are light and bully, and do not flow freely because the individual units tend to become entangled. These attributes add t o costs of seed cleaning, testing, storage and transport, and make it impossible to sow chaffy seeds evenly through conventional seeders. Ex amples are given of the structural diversity among chaffy grass seeds. The functions of hygroscopic awns and other appendages during establi shment are examined, indicating situations where intact seeds (includi ng chaffy appendages) should be sown, and others where structural modi fication to improve seed handling and distribution would enhance estab lishment. Processing methods to remove some or all of the chaffy appen dages are reviewed. Machinery available includes hammer mills, de-bear ders, brush polishers and de-awners, and cone, belt and filament thres hers, as well as equipment for flame treatment and aerodynamic conditi oning. Trimming of the normal chaffy seed units is generally preferabl e to the complete removal of caryopses, especially where caryopses are tightly held within the surrounding floral husk. Leaving a protective husk around the caryopsis reduces the risk of physical damage during processing and improves the reliability of field establishment under m arginal moisture conditions. Processing removes 40% or more of the ori ginal weight as inert matter. The advantages of higher seed quality an d more uniform seed delivery during sowing, as well as the compensator y effect of lower seeding rates on costs per hectare, should be emphas ised in price-sensitive markets. In some situations, artificial coatin gs applied to processed seeds may also facilitate sowing and improve t he competitive ability of establishing seedlings.