Fodder trees for drought conditions

April 2008
Professor Tom Barry leads a team at Massey University looking at drought-resistant plants and alternative food sources.

Using the scientific definition from Niwa in the last 31 years there were nine droughts. The East Coast is a lot drier and the projection is that the frequency and severity of drought is going to increase between now and 2080 and they are going to affect a larger area of New Zealand and areas that have not previously been affected. Farmers need to factor in the probability that drought will strike and have contingency plans for dealing with it.

Professor Barry says that traditionally farmers have addressed drought by altering their stocking policy. Beef and sheep farms producing a lot of stock will lamb or calve as early as possible and get lambs and calves off the farm early, which is de-stocking. Others consider bringing in bull calves from dairy farms, fattening them for meat production and selling only if drought occurs.

However there are other strategies, including using plants that can resist drought those with extra-deep root structures that can reach deeper into the soil.

A well-attested option is feeding willow and poplar foliage to livestock. Farmers have observed for many years beneficial results from their stock browsing soil conservation plantings but until recently there was no science to back it up. Farmers have been used to sawing down branches of poplars, willows and others trees such as tagaste (tree lucerne) to provide livestock feed in extreme drought conditions. This is time-consuming and potentially risky to the operator.

Massey set up experiments at Riverside Farm, in Wairarapa, on direct feeding to sheep of purpose-planted willow stems (Tangoio or Moutere) at 6000/ha on five 1ha areas which were previously unproductive on the farm. The rushes were sprayed out and the area electric fenced. Stakes 70cm long were buried half of their length at 1.2m intervals. Once good, leafy green stems had grown, browse feeding of ewes and lambs under controlled conditions showed:

Willows have higher energy values than summer pasture and contain condensed tannins which are absent from pasture. These differences in chemical composition help explain the responses to feeding supplements of forage willow.

Ewes that grazed willow browse blocks for 86 days in 2004, including mating, had higher reproductive performance than ewes that were mated on short, drought-affected pasture.

Forage trees can be used to prevent a decline in reproductive rate which would otherwise occur by mating ewes in short-drought-affected pasture.

It was calculated that 15% of the metabolisable energy and 65% of the condensed tannins consumed by the ewes on the browse blocks was from willow (paddocks had long herbage between willows).

Undrenched lambs on browse blocks had consistently lower dag scores and reduced worm burdens of some economically important internal parasites, than those grazed conventionally.

Sheep will eat material up to 3-4mm wide, while cattle will eat up to 9mm wide stems. Finer branches have the highest nutritive value. As time goes on the animals will eat thicker diameter material.

The willow plantings significantly dried out the wetter land and encouraged the development and growth of pasture species browntop, ryegrass, Yorkshire fog, lotus, white clover and creeping buttercup. These changes in herbage composition were apparent before the browse feeding of willow by sheep began.

Grazing browse blocks is not as effective as anthelmintic drenching for control of internal parasites, but the use of browse blocks could lead to a reduction in anthelmintic use and give a more sustainable grazing system.

A suggested management programme is:

Select unproductive sites, cut the rushes with a tractor-mounted mower about February, blanket spray with glyphosate in Late May and then rip and plant willow poles in June. Close the area from livestock, allow the trees to grow and the herbage to regenerate. Herbage can be grazed in the first winter. Trees need to be kept under browsing height, but should only be browsed once or twice in their second growing season. Exclude all livestock and close up in early October to protect developing tree leaf buds. Browse trees in well-established blocks in December, February and March/April, allowing about 8 weeks between grazing. Each browse block could be grazed for 7-10 days in this rotation. Graze hard with ewes in mid-May to eat down the tree stems and to remove stemmy pasture. Mechanical topping may be needed to reduce tree height. Graze lightly over winter and set-stock over lambing. The use of cattle on Riverside Farm to clean up in mid-May proved impractical, due to pugging and some willow stem breakage.

Safer harvesting of tree fodder in drought conditions

Tree supplements are normally cut from trees that were originally planted on the farm for soil conservation reasons . Farmers that do this regularly have developed safe cutting procedures . Many farmers who may want to use tree supplements in this drought don't know how to do it and do not have the proper gear . Greater Wellington Regional Council ( Masterton Office ) promotes the use of contractors who normally prune pine and other trees for a living , so they have all the safety gear and know good safe procedures . Council is making this service available to farmers. It estimates that about 1.5 million willow and poplar trees have been planted on the North Island East Coast over the last 25 years and that if trimmed this will yield about 36,000 tonnes of dry matter for stock feed . This would contribute significantly to feed that could be used in a drought, if there was a safe way of getting it down .