A Boggabri colleague in a 600 millimetre average rainfall environment (300 metres above sea level), with mainly lighter soils, has successfully established tropical grass pastures with 100 per cent success rate annually during the past 30 years.
Also none of the earliest sown stands show signs of deterioration of either perennial grass or winter legume content. Their property now has more than 2400 hectares of tropical grasses in more than 60 paddocks.
Key aspects of reliable success include a high standard of weed control, early perennial grass sowing (mid-October/early November depending on temperature), add legumes following autumn, shallow sowing, robust seed rates of untreated grass seed for economy, variety choice and soil fertility.
Summer annual grasses, like button, arm, barnyard and liverseed, plus existing perennials, while good feed, are competitors for soil moisture and commonly are the leading reason for new grass establishment failures. For high establishment success rate, a minimum of two and preferably three summers of totally preventing these weeds setting seed is important for driving down the soil weed seed bank.
Broadleaf weeds can be selectively removed from a new grass establishment, but grass can’t.
Winter crops, combined with sound summer fallows, are used to largely eliminate summer weeds that compete with emerging tropical grasses. These crops can also be used to clean up annual winter weeds like capeweed and Paterson’s curse via in-crop selective herbicides. If new winter legumes begin weed free they have a good chance of suppressing new invasions.
Recent research published in CSIRO Crop and Pasture Science, (2017, 68, 493–500, “Temperatures for seedling emergence of tropical perennial grasses) authored by scientists M. K. Egan, S. P. Boschma, S. Harden, C. A. Harris, and C. Edwards, confirms many of the tropical grasses suited to NSW establish at typical mid- to later-spring temperatures.
Relative early dry sowing maximises the probability of receiving good establishment rain in spring, summer, early autumn. For many areas, early sowing provides close to 100pc chance of receiving such rain.
Especially on lighter soils, best tropical grass establishment occurs from shallow sowing, from soil surface to 10mm, generally pressed wheeled in. A range of depths from 10mm (bottom of delved or cut via sowing implement) to surface helps maximise establishment.
Variety choice is critical for long term persistence in a given environment, including soil type. Be especially wary of mixtures that include species with a lessor reputation for long term persistence. If species as part of a mixture don’t last indefinitely, not only do they add unnecessarily to cost, but also leave gaps that take time to refill. For many medium and lower rainfall areas Premier digit grass for most soil types, bambatsi panic for medium heavy textured soils and a new NSW Department of Primary Industries selected panic variety, Megamax 059, take some beating.
Seed supply of tropical grasses is possibly likely to be better this year than last season. Several farmers have harvested seed as well as some regular suppliers. I have always preferred clean seed as one gets more seeds per dollar, often by a multiple margin. It is important to have seed quality data, including assurances of contaminants of species one may not be able to cope with.
Because of seed shortages last season, we successfully used seed with only 9pc germination. With sale price adjusted to reflect low germination and increased sowing rate to equate viable seeds sown per square metre results were fine.
Next week: Yield mapping technology: interpretation challenge.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
