Volume 27, 314

Tropical Grasslands (1993) Volume 27, 314–326

Tropical pasture establishment.
5. Improved handling of chaffy grass seeds: options, opportunities and value

D.S. LOCH

Department of Primary Industries, Gympie, Queensland, Australia

Abstract

Many useful grasses have 'chaffy' seeds characterised by a range of appendages: awns, sterile spikelets, and surface hairs or bristles. En masse, chaffy seeds are light and bulky, and do not flow freely because the individual units tend to become entangled. These attributes add to costs of seed cleaning, testing, storage and transport, and make it impossible to sow chaffy seeds evenly through conventional seeders.
Examples are given of the structural diversity among chaffy grass seeds. The functions of hygroscopic awns and other appendages during establishment are examined, indicating situations where intact seeds (including chaffy appendages) should be, sown, and others where structural modification to improve seed handling and distribution would enhance establishment.
Processing methods to remove some or all of the chaffy appendages are reviewed. Machinery available includes hammer mills, de-bearders, brush polishers and de-awners, and cone, belt and filament threshers, as well as equipment for flame treatment and aerodynamic conditioning. Trimming of the normal chaffy seed units is generally preferable 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 marginal moisture conditions.
Processing removes 40% or more of the original weight as inert matter. The advantages of higher seed quality and more uniform seed delivery during sowing, as well as the compensatory effect of lower seeding rates on costs per hectare, should be emphasised in price-sensitive markets. In some situations, artificial coatings applied to processed seeds may also facilitate sowing and improve the competitive ability of establishing seedlings.