Southern NSW farmers travelling north in winter, often comment on the typically dry grass northern pastures and how unproductive they look.
These are typically remnant native summer grasses, or tropical grasses, sometimes with dry weeds like fleabane in them.
Underneath this generally low quality dry material, often more than 0.5 metres high in mid-winter, especially following good summer rains, can be next to nothing or a thriving winter legume and annual grass pasture.
These contrasts depend on management and seasonal conditions, and can have an enormous impact on livestock productivity. Soil nitrogen build-up, important when pasture is part of a cropping rotation, can also be impacted.
Grazing management to reduce heavy summer grass coming into late autumn and winter is an important aspect but not necessarily the main factor.
Soil fertility is also important, as is the winter legume species component and how it is managed.
Summer grass dry matter level coming into late autumn needs to be not so dense that it prevents sunlight from reaching ground level, a likely requirement for winter legume, like sub clover and medic germination.
For many grass species, native and introduced, this is likely to be around 3t/ha dry matter or lower.
On the other extreme, with no dry grass residue, winter legume establishment can also be delayed and slower.
Relatively open dry grass residue can help protect emerging winter legumes and grasses from drying winds and evaporation and helps keep the top soil moist for longer going into dry weather.
Temperatures tend to be less extreme, frost and heat, where residue cover is moderate.
Following good summers, slashing is often advocated as a means of reducing carryover dry matter levels.
My experience of late slashing, which is well into winter, commonly only has a marginal impact on winter legume establishment.
If you are slashing, it is more likely to assist winter legume establishment if carried out well before late autumn.
This timing allows for some summer grass regrowth, mainly not a bad thing, but is less useful for eliminating weeds like fleabane (more likely to regrow and seed).
Winter legumes under dry summer carryover commonly closely reflect soil fertility.
No matter how ideal the level of carryover summer feed is, if soil deficiencies like sulphur and phosphorus are not addressed, legume growth will be poor.
Also, their contribution to building soil nitrogen, important for future summer grass feed quality, as well as for building soil nitrogen for future crops, will also be poor.
I often am told "that paddock down there is only for store animals and for livestock not requiring good feed quality" because it never grows good legumes.
Generally, a story of soil deficiencies is not addressed.
Winter legume species and variety selection are also an important part of good winter legume growth growing amongst dry carryover feed.
Species are commonly soil pH related.
Alkaline soils with pH above 6.5, for example generally best suit a range of annual medics.
Moderately acidic soils suit species like sub clover and very acidic soils, including those with acid sub soils, generally suit species like serradella and biserrula.
Variety choice within a species of winter legumes is also important.
Hard seed levels reflect a variety's ability to have carryover seed should a drought or run of droughts occur.
For example, the recent three-year drought in many areas (2017, 2018 and 2019) emphasised the importance of varieties with high levels of hard seed and prior management that allowed a good soil seed build-up.
Also important is a winter legume's maturity for a given environment.
Early maturity means early flowering, for example, early August onwards for many environments.
Early maturity allows at least some seed set in a dry spring compared to a mid or late maturing variety setting very little or none if ends early.
For colder areas like the tablelands, flowering too early is not necessarily a good attribute as low temperatures can prevent early flowering.
Grazing management of winter legumes is also important, especially in the first year or so to ensure a good build-up of soil seed reserves.
Next week: Mixed species crops versus single species crops.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact 0428 752 149.
