While there is a large range of winter legume species and varieties available, it is important to choose carefully, especially if long term persistence and good productivity is required.
Winter legumes are largely those that germinate in autumn, grow through winter and into spring, then set seed in preparation for germination the following autumn. Important aspects to consider include likely flowering starting date, suitability to various soil pH levels, hard seed content level, likely productivity, tolerance or otherwise to various diseases and pests, maybe suitability to aspects like waterlogging and grazing tolerance. Feed quality and maybe bloat tolerance are also important.
It is prudent to select varieties that are able to set seed in years tougher than long term average rainfall might suggest as best for a given area.
For example our farm is in what might be termed a typical medium rainfall environment (625mm average annual rainfall, with summer months on average receiving a bit more rain than winter months) where mid-season winter legumes would seem to be the main choice.
Yet many years of research, by NSW DPI district agronomists, including a long term trial in the 1970s, '80s and '90s on our property, identified early maturing hard seeded Dalkeith as by far our best sub clover variety on moderately acidic soils. And now tropical grasses are a big part of our pasture base, the need for earlier maturity in winter legumes is even more important.
Dalkeith, and similar maturing varieties in many other legume species, begins flowering around August 10 onwards. If spring is dry it will generally set a reasonable amount of seed and if spring is good it will continue flowering well into October. A high level of hard seed means once a soil seed bank has built up there will be an adequate level of seed to allow persistence over a run of droughts (for example 2017 - 2019) or a short to moderate cropping phase.
Researchers working in the tablelands have found medium maturing hard seeded sub clover, and probably also for species like serradella on the more acid soils, better suit than early maturing types.
Flowering too early in colder areas probably sets seed poorly when temperatures are too low. In contrast in drier and warmer areas well to the west of us, commonly better suit even earlier maturing varieties, for example Nungarin sub clover, which is around 10 days earlier flowering than Dalkeith.
Soil pH, and on acidic soil, level of aluminium toxicity (that increasingly becomes an issue as soil pH drops), is an important winter legume species and variety consideration.
Barrel medics tend to suit where pH (calcium chloride method) is 6.5 or higher. Several varieties have high levels of hard seed and maturity ranges from early (for example Caliph) to mid to late maturing (for example Sephi). Some varieties have good tolerance to aphids, a common issue in late winters and springs.
In other news:
One of the major breakthroughs in the past few decades is the release of winter legume species with excellent ability to grow in soils that are acidic in both or either the top and sub soil. For example serradella has proven persistent and productive in soils down to 4.2 pH with high levels of aluminium toxicity.
Several varieties have high levels of hard seed and there are varieties that vary from early flowering to mid and late flowering. Our own property is a good example where early to mid-maturing varieties like King and Elgara have persisted through drought and perform well in average to good years.
Biserrula is also increasingly being appreciated as an acid soil tolerant species with both an early hard seeded variety (Casbah) and a mid-season variety. Like with serradella, suitable rhizobia types for these species also are able to perform well in acidic soils.
Other species with good hard seed levels and acid soil tolerance (although not as good as serradella) to various degrees include gland, bladder, arrow-leaf, balansa, woolly pod vetch, rose clover and most white clover varieties.
It is sensible to seek out seed supplies now for next year's sowing, as commonly by next autumn supplies may be pretty tight.
Next week: Best approach to future farming.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
Have you signed up to The Land's free daily newsletter? Register below to make sure you are up to date with everything that's important to NSW agriculture.
