DETAILED research by Wagga Wagga DPI research agronomist Dr Belinda Hackney and interstate colleagues including Prof. John Howieson, Dr Ron Yates (Murdoch University) and Dr Angelo Loi (DPIRD WA), with significant farm adoption, shows frequent big advantage of sowing winter legumes ahead of autumn breaks, notably the case with hard seeded species like biserrula, serradella and gland clover.
Sowing in January-February with appropriate technology of unprocessed hard seed with rhizobia impregnated clay granules (ensuring long survival), has resulted in legume establishment on first autumn rains and generally their development way ahead of more traditional sowing after the autumn break. The quantity of winter-spring feed from summer sowing has commonly been much higher due to earlier establishment.
Early sowing of unprocessed seed, either direct drilled or where appropriate even top-dressed, is a widespread practise in Western Australia where farmers harvest their own seed and don't process it but simply sow dry in January or February. Early sowing allows seed to break down 'hardness" naturally via normal temperature and moisture fluctuations. It makes sense, especially for newer hard seeded species, to likewise plan an area for future seed harvesting.
Rhizobia bacteria, so vital for legumes to convert soil air nitrogen into legume protein and build soil nitrogen, normally only survive a short period when applied to seed by more traditional ways like use of a peat slurry or propriety coating.
Research by Dr Hackney and colleagues has shown that specialised clay granules impregnated with inoculum specific to legume species are successful in achieving nodulation when applied well ahead of germination. The advocated application method is to mix the clay-based product with seed and drill shallow.
These clay granules with appropriate rhizobia have been successfully used in summer sowing and for later so-called conventional sowing for more than a decade in WA and parts of southern NSW with good results. Only one manufacturer, Alosca, WA, supplies this type of product so it is important to telegraph requirements, either direct to manufacturer, or via local agribusiness outlet in spring or at the latest early summer prior to sowing to ensure supply.
The early sowing strategy of unprocessed seed makes sense for introducing specific legumes with their specific rhizobia into long term pastures like native grasses or introduced perennials, or where short term annual legumes pastures are used in a cropping rotation. Adding rhizobia via clay granules to legumes with poor or no effective nodules, a common situation, is also sound strategy to upgrade them.
Ordering early is also a sound strategy if sowing tropical grasses this coming spring. Fortunately with the good mid to late summer and autumn rains in many districts, seed of Premier digit and Consol lovegrass should be readily available.
A good strategy for tropical grasses, provided summer grass weed levels are largely reduced by good fallow management over the past few summers, is to sow dry at the earliest part of the sowing window (for many areas late October early November) regardless of rain forecasts. Unlike temperate perennials, or lucerne, tropical grasses mostly only begin to germinate on rains following sowing.
Early sowing means new pasture has up to five months to receive germinating rains. This past year we sowed early November and did not receive germinating rains until mid-January onwards. But seed was in the soil at the right depth and germinated well after rains. In other years rain has fallen soon after sowing and stands have been fully productive within three months.
It is especially important to check seed quality before purchase. I like to know source of seed to minimise risk of weed contamination. Seed germination and purity is also important. We prefer to sow un-pelleted seed, generally far cheaper on a per-seed basis. Also its commonly preferable to buy seed of variety and species you know is best for your location rather than varieties not long term persistent to a given environment
Note with tropical grasses it's generally best to sow winter legumes into them separately in late summer autumn after establishment.
Next week. More tips for future drought preparation.
- Bob Freebairn, agricultural consultant, Coonabarabran. Email email@example.com 0428 752 149.