Tropical perennials can fill blanks if rains fail

Filling the blanks with tropical perennials


Cropping
Outstanding tropical grass recovery after good early March rains following a dry summer. Tropical grasses combined with winter annual legumes can be long term persistent, productive, high quality, and suit most of NSW.

Outstanding tropical grass recovery after good early March rains following a dry summer. Tropical grasses combined with winter annual legumes can be long term persistent, productive, high quality, and suit most of NSW.

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Tropical grasses combined with winter legumes are opportunistic, and will capitalise on rainfall that may not match the demands of winter annuals.

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WHILE lucerne is a great pasture plant that for most areas provides green feed whenever it rains, so can tropical grasses with winter legumes.

A big feature of tropical perennial grasses is that well managed and selected they can last indefinitely, suit many soils that don’t suit lucerne (deep acidic, shallow, temporarily waterlogged), don’t drop leaf in a dry period and can also be very productive.

Grazing management requirements are not strict, but they do best where good ground cover levels are maintained and periodic rest and recovery periods are allowed.

When autumn breaks, late tropical grasses provide green feed from rain too early for that needed by winter annual legumes.

If springs are dry or cut out early, tropicals quickly provide feed from rain too late for winter annuals.

Production from the tropical grass component varies according to rainfall and how seasons develop. In 2016 many areas experienced a great winter and spring followed by a dry, hot summer.

Legumes such as sub clover, serradella, gland, biserrula and rose clover often ended the season with over four tonnes to the hectare dry-matter.

These largely dried soil water levels, providing little moisture for tropicals unless or until significant summer rains occurred.

However quality of dry feed of the winter legumes was commonly maintained through summer as little rain caused it to break down.

Periodic small rain events, especially on lighter soils, provided good short bursts of green tropical grass feed that added to quality of the dry carryover herbage.

In contrast the previous several years mainly experienced dry springs, often combined with late autumn breaks for many areas, including ours.

Winter legumes (and grasses plus broadleaf herbage including weeds) were late to get away and commonly closed down early, although species like serradella tended to hang on much longer into a dry spring. 

In these years tropical grasses commonly compensate the often lower productivity of winter legumes. Tropical grass growth cycle for many environments goes from early spring right through to the end of autumn and sometimes even into early winter.

They can provide quick feed after a late spring rain that is too late for annual winter legumes that have “shut down” because of the dry spring.

They can respond quickly to summer rains and early autumn rains, often too early to sustain winter legume establishment.

Most of NSW, even southern areas, generally receive periodic rain in late spring, summer and early autumn. Winter annual pastures commonly use such rainfall inefficiently or not at all.

Such rainfall is also a ready target for summer weeds if competitive summer growing pastures are absent. Summer growing tropicals are the best way to combat many weeds, including burrs, African lovegrass and Coolatai grass.

Like all pastures, good soil fertility is a vital part of combined tropical grass and winter legume. In our own example these comprise 40 per cent of our pasture base and play a vital part of our fattening business.

And like for most pasture types, establishing the perennial component is critical.

We only sow perennials after at least a two-year previous cropping cycle (in our case dual-purpose winter cereals), where the summer weed seed bank is largely eliminated. Annual legumes can be established relatively easily, but perennials require weed-free conditions.

Tropical grasses mirror many native summer growing species. For most areas however the best of the introduced species tend to be far more productive, as well as long-term persistent. 

Next week. More research finds paddock elevation differences has big impact on crop yields.

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