Down To Earth: Choosing pasture legumes for next autumn sowing

Three very dry years (2017-19), followed by three wet years (2020-22) and a very dry winter spring this year are testament to that.

Legumes can build soil nitrogen by around 25 kilograms per hectare for every tonne/ha of legume drymatter production. Plus they provide high protein, high quality feed.

Soil nitrogen is important for the grass component, as well as for crops if part of a rotation.

I am not advocating willy-nilly mixtures of often poorly thought out combinations of species and varieties, including some by seed companies.

Commonly, these include species and varieties with no hope of help in a specific pasture situation.

I recall an example where over $300/ha of pasture seed was recommended but the end result was that 90 per cent of 10 species failed.

Sometimes these mixtures include summer and winter species that, even if suitable, should be sown at different times.

Regardless of species or variety maturity a most important requirement for all long term annual legumes is at least a good level of hard seed.

Hard seed means seed that won't germinate out of season. For example, from summer rains if a winter species.

The exception is untreated hard seed of species like serradella and biserrula where summer sowing does not lead to false early germinations.

Also critical for adding legumes to a pasture is that their appropriate root nodule bacteria (rhizobia) is properly added with them.

For example, inoculant group Al for lucerne, SRDI736 lucerne on acid country, AM for many but not all medics, C for sub clover, balansa, bladder, arrowleaf, rose and gland clover, E for woolly pod vetch, S for serradella and WSM1497 for biserrula.

Legumes not having access to their appropriate rhizobia fail to build soil nitrogen and commonly are poor growers.

Applying rhizobia with new legume sowings is as important as choosing the best species.

Granules via Alosca pellets added to pasture seed at sowing - while a bit expensive - is a more reliable method of ensuring rhizobia survival, especially if sowing dry and if rain doesn't lead to germination for some time.

An example of benefits of combining selected mixed species winter legumes is from our property east of Coonabarabran, in the upper latitude part of central west NSW.

Soil type of most paddocks can vary, even within a short distance, in top and sub soil, from pH 4.4 to 6.2.

Our winter legume mix includes yellow serradella, slender serradella - as long as we can find any seed - sub clover, gland clover, rose clover, arrowleaf clover and balansa.

Not all of these are universally important but have their niche.

Yellow serradella grows and persists well in moderate pH to highly acidic areas.

In dry years it has grown into spring longer than all but biserrula, because of acid soil tolerance and fast-rooting depth.

Early maturing hard-seeded varieties king and elgara flowered from early August onwards this year and set useful levels of seed. Because good seed set occurred in better years, a missed seeding is not critical anyway.

Slender serradella is especially waterlog-tolerant and was the standout species in the wet areas in the wet years.

Its high, hard seed levels helps guarantee its persistence until the next wet winter year.

Sub clover is good on the medium loams and less acidic lighter soils and coexists in these parts with biserrula and serradella.

Hard-seeded, early-maturing varieties like dalkeith allows some seed set in most but not all drier years.

It is productive in good years and like many subs has useful short term waterlog tolerance.

Rose clover, a much underrated species, also suits many soils, is productive and is proving long-lasting.

Hard-seeded arrowleaf is great in good springs and can go unnoticed in drier years. Barrel medic suits our heavy soils.

Because seed of species like serradella and biserrula commonly come from Western Australia, it is best to order seed early to avoid unnecessary delays at critical sowing opportunities.

Much the same can occur with pelleted form inoculum. Many other important factors include grazing management (critical for aerial seeded varieties) and soil fertility.

Next week: Recognising outstanding crop research.