Winter an opportune time to check legumes

Strategy time for legumes


On Farm
Early winter 2017 view of annual legumes on John and Caroline Robinson's property, “Coolowri”, Upper Horton. Legumes drive winter feed production as well as provide nitrogen for summer grasses.

Early winter 2017 view of annual legumes on John and Caroline Robinson's property, “Coolowri”, Upper Horton. Legumes drive winter feed production as well as provide nitrogen for summer grasses.

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If your legume count is down, now is the time to fix the problems. Next summer's nitrogen levels are depending on you.

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LEGUME content and vigour are important pasture productivity attributes.

Not only do they provide quality feed for the pasture, but equally important provide nitrogen for the grass (perennial or annual) component.

Now is a good time to assess for legumes and to devise strategies if their presence and health is lacking.

I find it relatively rare not to find some level of legume content in most pastures including native, introduced temperate and tropical perennials, as well as annual species (generally those after a cropping phase not sown back to perennials).

Naturalised clover such as burr medic, ball clover and narrow leaf clover can be important legume pasture components and can provide a similar role (quality feed and nitrogen building) to introduced species such as sub clover serradella and the like.

A major cause of poor legume growth, naturalised or introduced species, is soil deficiencies.

If significant deficiencies of elements like sulphur and phosphorus exist their growth will be stunted, commonly with mid-winter yellow and reddish leaf appearance.

Commonly one has to look hard to find severely deficient plants, but if there, they can be found.

Research shows there is no alternative to applying fertilisers that contain adequate levels of missing soil elements that are in an available form or that relatively quickly convert to an available form after application. No research has supported other than this basic rule. 

Single superphosphate has around 8.6 per cent available phosphorus and 11pc available sulphur and has for many years been a mainstay fertiliser for pastures deficient in both these elements.

Alternative products can easily be benchmarked against single super if these are the main missing elements. 

Animal manures like poultry are variable in nutrient content for a variety of reasons. Typically phosphorus content varies from 1.0 to 2.0pc, with about one third of this being in an immediately available form and the majority of the rest slowly available.

Sulphur content of poultry manure is normally around 0.4pc. 

Rock phosphorus on its own is high in phosphorus but mainly in an unavailable form.

There is no sulphur in rock phosphate. Always check reliable analysis of products being marketed to correct soil deficiencies.  

If legume density is low (scattered rather than continuous), it is best to plan to add the most suitable species next autumn.

Ideally have them in or at least on the ground prior to the autumn break to ensure they germinate on equal terms with existing pastures.

Adding them after the autumn break commonly means they are trying to establish against existing vegetation, such as annual grasses and other herbage.

If suitable species already exist but are thin in population, grazing management to ensure maximum seed set this coming spring is important.

For example if it is an acid soil, one serradella plant can set thousands of seeds if allowed to fully develop but will set zero seed if grazed into the ground flowering time onwards.

Legume rhizobia health is a critical issue with plants not thriving unless coexisting with their appropriate strain.

Adding rhizobia via infused clay pellets or via added seed inoculated with fresh peat and into moist soil can solve this issue.  

Sometimes species such as sub clover can now be assessed for problems such as viruses (commonly reddish appearance and stunted) although symptoms of these can be confused with nutritional problems.

Next week. New varieties lift production of most winter crops.

  • Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
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