Because of drought hardiness and ability to respond to rain over spring, summer and autumn, interest in establishing tropical grass pastures is increasing rapidly.
Our enquiries indicate interest is strong in most districts, including southern as well as northern environments, western, slopes, and tablelands through to coastal.
A few important aspects, discussed here, can help prevent establishment failures, a waste of money and frustration and disappointment. While some people have got away with shortcuts, reliable establishment depends on getting the basics right. Tropical grass pastures can last indefinitely if well established with many stands now well over 30 years old and still performing strongly.
Be especially careful of species and variety selection. All too commonly mixes marketed for a given area contain a good portion of varieties not suited to it. Literature, seed company and state agencies, commonly are not clear as to what are the best varieties for a given area. However we do know, from many years of NSW DPI trials, as well as what has happened in the field, that there are big differences in species and variety persistence as well as productivity.
For example for much of inland NSW, from areas with 400 millimetres to over 700mm average annual rainfall, Premier digit grass has been a standout variety for medium to lighter soils, including acidic ones. Consol is even more hardy for lighter acid soils. Bambatsi panic has generally wide suitability to heavy soils. While it sounds good to have a "smorgasbord" of species in a pasture, it is not much sense to sow such a pasture if many of them are not going to last.
A key establishment aspect is sowing into weed free paddocks. Hence why we emphasise not allowing summer weeds, especially grasses, to seed in fallows or summer crops in at least the two summers, and preferably three, preceding sowing. While suitable tropical grasses are strong against weeds when well established, they are easily out-competed by them as seedlings. Broadleaf weeds can be killed by herbicides but grass weeds can't as they also kill seedling tropical grasses.
We always sow early, around mid-October to early November for our environment. Early sowing requires high standard weed control. Commonly sowing coincides with dry top soil but good subsoil moisture. The aim is for germination to occur from the first following decent rain event. Last season that follow-up rain did not come until three months later but as in previous years proved successful. In some years a good rain falls within a few days of sowing with a fully productive stand in three months.
Some springs/summers are pretty tough, so provided seed costs are reasonable, we will sow around 4.0 kg/ha. That's a lot of seeds per square metre but tough seasons can lead to a lot of seedling wastage. In a tough establishment year these higher seed rates have been worth it. In a good summer sowing at half these rates would be fine.
Seed quality is important. We have successfully used clean unpelleted seed, by far the best value for cost per viable seed. Some pelleted seed can have high levels of pellet material such as fine lime, which means much fewer seeds per kg. Where a seed mix may only contain 50 per cent of the variety one requires, plus seed is pelleted, the end result is a cost per viable seed (given similar germination rate), compared to a straight batch of clean seed, several times higher. Big dollars.
We mix seed with fertiliser and it is sown via the fertiliser distributor. Shallow sowing is vital, from the soil surface to no more than 1.0cm. A following press wheel helps firm soil around the seed, often a good help for germination.
Tropical grasses establish best if soil fertility is at least reasonable. Important for a tropical grass is nitrogen as well as phosphorus and sulphur. Depending on soil test a good sowing fertiliser can be a product like Granulock 15 that contains sulphur, phosphorus and nitrogen at reasonable levels.
We have always added winter legumes in the late summer or autumn following tropical grass establishment unless there remained a good level of their soil seed reserves after the cropping phase.
Next week: Grain yield responses to deep phosphorus fertiliser placement.
- Bob Freebairn is an agricultural consultant, Coonabarabran. Email robert.freebairn@bigpond.com or 0428 752 149.
