Drought-breaking rain helps pastures bounce back

Drought-breaking rain helps pastures bounce back

Cropping
Tropical grass pasture (Premier digit grass) prior to drought-breaking rains received towards the end of January. Dormant but previously well managed.

Tropical grass pasture (Premier digit grass) prior to drought-breaking rains received towards the end of January. Dormant but previously well managed.

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Well managed lucerne and tropical grasses have been by far the quickest to respond to rain.

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Good cattle feed 14 days after an almost definite drought-breaking rain, first received in mid-January, occurred on several properties in ours and other districts. This was followed by further widespread rains in February. That rapid recovery is an example of how quickly pastures can recover, given appropriate grazing management as well as pasture type suited to make use of such rain.

Well managed lucerne and tropical grasses have been by far the quickest to respond to rain. In some cases, native grasses have also responded well, although in many environments they are well behind introduced tropicals like Premier digit, Consol lovegrass and bambatsi panic.

Temperate perennials like phalaris, especially in other than normally mild temperature environments, commonly don't respond well to summer rains until temperatures cool and they (the plants) assess the autumn break is occurring.

But within a species, for example, lucerne or Premier digit, response to summer rain has varied considerably, even with the same amount of rain received. For example, in our area, we have seen Premier digit grow at a rapid rate of 150kg/dry matter a day and accumulate within four weeks over 4t/ha. In contrast, other stands have over the same period grown less than 1.0t/ha.

Andrew Freebairn with daughters Georgia and Mia, check the same pasture as above just over four weeks post the beginning of drought-breaking rains.

Andrew Freebairn with daughters Georgia and Mia, check the same pasture as above just over four weeks post the beginning of drought-breaking rains.

In the case of lucerne, some stands have grown at similar rates as Premier digit, with grazing management critical for recovery rate. Quality of both has been high, with lucerne well over 20 per cent protein and digit at 16pc or so. However, we have also seen lucerne stands not survive the drought with only weeds growing in the paddock. In other cases, plant survival has been OK, but regrowth has been slow.

A major factor in plant recovery is the level of stubble retained over the drought. Even relatively low residue levels of perennial plants, with their intact root systems, effectively trap heavy rain events. It's a bit like blotting paper, with moisture retained against reasonable gravity.

Well managed lucerne and tropical grasses have been by far the quickest to respond to rain. - Bob Freebairn

Cropping paddocks with retained ground cover have also helped conserve rainfall from moderately heavy rain events. The intact root system attached to above ground plant material has also helped with moisture capture and helped prevent wind erosion.

Grazing management that combines allowing reasonable plant recovery prior to grazing with adequate ground cover, especially for perennial plants, also helps with plant survival as well as plant recovery. Generally, after grazing, perennial plants use their root reserves to recommence growth before they gradually replenish those reserves. Detailed lucerne research for example, by NSW DPI, shows after grazing, plants draw on root reserves for the first seven or so days and then up to about day 45, replenish these reserves.

Lucerne two weeks after drought-breaking rains on David and Cynthia Bruce's property "Uliman South" Coonabarabran.

Lucerne two weeks after drought-breaking rains on David and Cynthia Bruce's property "Uliman South" Coonabarabran.

Not all species are so vulnerable that they require strict grazing management periods followed by longer no-graze recovery periods. But a flexible system of rotational grazing keeps most species reasonably resilient and able to cope when droughts occur.

Post-drought rain grazing management is also important. Appreciating that plants have gone through a stressful time with their root reserves likely low, it is best to allow them a period of regrowth before grazing to rebuild these reserves. Regrowth will be faster if a good level of leaf material is allowed to develop to best utilise sunlight, an important aspect of growth.

Good soil fertility is also an important aspect of pasture recovery. Not correcting deficiencies like phosphorus and sulphur, and for non-legume plants nitrogen, means root depth and mass will certainly be far less, equally important, grazing quality will be lower.

Next week: Weeds following droughts.

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