The final instalment in our four-part series looking at the value of legumes in dryland farming systems. This week is all about sub-clover.
With the correct management, annual clovers can be some of the most valuable forages in a dryland forage system.
They provide high quality, protein-rich feed early in spring, which drives lactation and lamb growth rates.
Subterranean (sub) clover is the most common annual clover and is endemic in soils throughout east coast hill country and plains, thanks to over-sowing and drilling that took place in the 1960s.
Despite this, Dick Lucas from Lincoln University says that, for farmers to make full use of this clover, it needs to be actively managed. This has been highlighted in the “Maxannuals” trials run on a particularly stony site on Ashley Dene.
In autumn 2013, four different pasture species were established with two varieties of late-flowering sub clover (Denmark and Rosabrook), with and without the top-flowering balansa clover. Tonic plantain and Nomad white clover were also included in every mix.
The mixes were:
- Cocksfoot and sub clover
- Cocksfoot, sub and balansa clovers
- Ryegrass, fescue and sub clover, and
- Ryegrass, fescue, sub and balansa clovers.
The plots were grazed by ewes and lambs in spring, and these clovers drove growth rates in excess of 300gm/head/day in early spring. The plots were closed up and allowed to flower and set-seed in early summer. Weaned lambs were returned to the plots to graze in late summer and autumn. Ewes and hoggets were used to clean up and maintenance graze the plots over late autumn and winter.
Extreme drought impacted on the trial, with the ryegrass dying in its first year and attempts to re-establish it failed.
Seed bank exhausted
Within three years, drought and false strikes decimated the subterranean clover seed bank in the trial area – from about 600kg seeds/ha to just 5kg seeds/ha.
In 2013, after allowing the clovers to set-seed, there was 600kg seeds/ha in the soil. An extremely dry spring in 2014 meant this was reduced to 250kg/ha.
In January this year, a rainfall event triggered a false strike, with some seeds germinating. A subsequent lack of moisture meant all the seedlings were dead by early March. A second false strike occurred in March and, again, the seedlings all died. In September, the seed bank was less than 5kg/ha.
Two years ago, the cocksfoot/clover treatment contained 25% clover. The plantain – which persisted after the ryegrass died – contained 40% clover. Now there are an average of 10 sub clover plants per metre square, while Dick says there should be more like 500 plants per metre square.
As well as the false strikes, there was inadequate soil moisture and two late-flowering varieties of sub were used in the treatments. Late-flowering subs take five weeks to reach maturity and, with extremely dry conditions, the plants wilted before they could produce seed. This meant mining the bank of sub clover seed in the ground to produce plants the following year.
Sub clover will be oversown into the trial area at 10kg/ha in early March 2017.
This time, mid-flowering cultivars will be used, so the burrs are mature by the end of October – before soil moisture completely disappears.
Management will focus on allowing these new seedlings to set seed, so the area will only be lightly grazed in that first spring.
Sub clover management key points:
- Choose the cultivar with the right flowering date for your environment.
- Understand the plant and its lifecycle.
- Sub-clover can be over-sown in autumn.
- Aim high: 500 plants/m2 is aspirational, but 200-300 plants/m2 is adequate.
Herbicides have different effects on different cultivars.
Controlling weeds in newly-established sub clover can be a challenge, with just one herbicide (Headstart) recommended for use on sub clover in New Zealand.
A herbicide trial set up this year is looking at chemical options that will control weeds and allow the clover to reach its yield potential.
Four varieties of sub clover were established: Antas, Denmark, Monti and Narrikup, along with Huia white clover. The treatments were drilled in March, but the dry autumn meant emergence was delayed into May. Seedlings were then sprayed in either June (at 1-2 trifoliate leaf stage), or July (at 3-4 trifoliate leaf stage).
Preliminary results from the first spray treatment show that herbicides have different effects on different cultivars.
- Antas – while the most susceptible in terms of yield decrease – remained the highest yielding.
- Narrikup was the most tolerant and maintained high yields.
- Denmark was tolerant, but low yielding.
- Monti has not thrived in the dry environment, but was tolerant to herbicide.
Headstart and another herbicide, Basagran, both provided effective weed control, with minimal impact on sub clover.