Like many farms across NSW, soil type commonly varies across a paddock, let alone across a property.
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Other issues, like elevation and slope direction, can also add to considerable property climate differences.
Seasonal variability, from too wet to too dry, impact species and variety choice.
So do aspects like disease, for example, soil fungi, pests like aphids, and susceptibility to herbicides.
As an example, our property soil type varies from very acidic, combined with subsoil acidity, to neutral pH, and elevation differences of 40 metres, which impacts on frost severity and frequency.
In a year like we have had, some areas can be very wet for extended periods - all impacting pasture choice.
Most but not all medic species tend to favour soils with a pH (calcium chloride method) of 6.5 to 8.5.
In many areas, the dominant species is naturalised burr medic (Medicago polymorpha) and regardless of what is sown, it commonly gradually dominates high pH soil pasture paddocks.
This is not necessarily a bad thing, although an issue for wool contamination.
Varieties have been released that have spineless pods, for example, Santiago.
Barrel medic, a similar species with varieties like Caliph, also has spineless pods and a range of varieties with good to high hard seed levels.
Sub clover, especially in medium to higher rainfall areas, remains the most overall dominant winter legume with a large range of varieties.
Overall sub clover suits soils with a pH 4.8 to 6.5, but "brachy" types (Brachycalycinum) suit more alkaline soils with pH up to 8.
While many sub-clovers have shown reasonable semi-water logging tolerance this past year, Yanninicum types especially suit these conditions.
For all winter legume species, selecting varieties with high hard seed content is vital for long-term persistence.
For example, many areas experienced three consecutive years of drought from 2017 to 2019 with little or no seed set.
Provided good soil seed reserves existed before the drought, generally, seed levels provided excellent regeneration in 2020 when the drought broke for varieties with good hard seed levels.
Also important for whatever the species, is the right maturity of a variety for a given area.
Quick maturing varieties generally best suit drier western areas and long maturity for areas with milder and later springs.
However, even in so-called better rainfall areas, it is commonly a good idea to have earlier maturing varieties as part of the mix to cater for runs of drier years.
For example, our property, in a 625 millimetre average annual rainfall area, with Dalkeith, an early maturing sub clover, our dominant sub.
Examples of earlier hard-seeded varieties include Nungarin sub clover, Caliph barrel medic, Prima gland clover, Cefalu arrowleaf, Casbah biserrula, Bartolo bladder and King, Yelbini, Elgara and Santorini yellow serradella.
Low soil pH, and level of aluminium toxicity (that increasingly becomes an issue as soil pH drops), are important aspects for species and variety consideration.
Not only are topsoil pH and aluminium levels important, but also knowledge of the subsoil.
Lime can correct topsoil's low pH but generally only has a minimal effect on the subsoil.
Therefore the importance of choosing varieties with tolerance to low pH.
Serradella, and also in many situations biserrula, have proven persistent and productive in soils down to 4.2 pH with high levels of aluminium.
Several serradella varieties, including pinks and yellows, have high levels of hard seed, and varieties range from early to late flowering.
Most varieties don't like waterlogged conditions for long periods.
One serradella species, varieties Jabala and Westport, has good waterlogging tolerance.
Unfortunately, the seed is pretty scarce.
Many other winter legume species are available with a range of good characteristics, including good hard seed levels and acid soil tolerance (although not as good as serradella).
Balansa has excellent semi-waterlogging tolerance.
Gland, bladder, arrow-leaf, woolly pod vetch, and rose clover have good acid soil tolerance and hard seed levels.
Many other factors not covered also impact variety choice.
For example, some need more grazing care, especially at flowering, to ensure seed set.
Next week: Grain sorghum has a wider sowing window.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
