Legume management after February rain

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Posted on behalf of Prof. Derrick Moot.

Many east coast areas of New Zealand have had 20-100 mm of rainfall in the last week or so with more forecast. This unusual mid-summer situation has messed up my holiday – but more importantly can lead to some management issues that need to be considered for lucerne and sub clover. Lucerne will respond rapidly to the rainfall and give you a flush of fresh growth. It is highly palatable but has three issues to be aware of at this time of year:

  • Lush lucerne now brings us back to spring like conditions so treat it with caution – think about roughage, salt and potentially mowing in front of the animals if you had more than 30 mm of rainfall.
  • If you were dry before the rain there is an increased risk of high nitrate in the lucerne – so try and start grazing in full sunshine when that nitrate has been converted to protein in the plants . Avoid grazing on dull/overcast days immediately after rainfall especially with lambs.
  • The lucerne looks great and will have arrived at a perfect time for mating. However, these hot humid conditions are exactly those that increase the coumesterol levels in lucerne which can reduce ovulation rates. To reduce risk think about grazing the lucerne up to two weeks before the ram goes out – at that time move them onto a grass based pasture. Ovulation can be reduced by up to 25% so if you have other feed on hand this is the year to use it. Once mated the lucerne is fine to be grazed again.
Fantastic lucerne stand recovered after recent rain – avoid mating on it! Excellent feed for cattle, finishing lambs or growing hoggets. Take ewes off such a stand two weeks before the ram goes out. (Photo supplied by Fraser & Shelley Avery, Bonavaree, Marlborough).
Leaf spots on the lower leaves and the high humidity in the canopy cause elevated coumesterol that can reduce ovulation rates. (Photo supplied by Fraser & Shelley Avery, Bonavaree, Marlborough).
New lucerne regrowth after rain can have high nitrate so wait until sunshine returns before grazing. Avoid grazing on dull days while it is still raining. There will be a lot of nitrogen in the soil from urine returns from previous grazing rounds in spring and summer that is then taken up by the plant as nitrate – the suns energy is required to convert it to protein. (Photo supplied by Fraser & Shelley Avery, Bonavaree, Marlborough).

The best pasture to use for mating this autumn may actually be sub clover based. I have had many reports of sub clover striking now however, it is too early to survive into autumn unless more rain falls. To increase the chances of the current sub clover strike making it to autumn stay off it until at least 3-4 true trifoliate leaves have developed on the plant and when you pull it leaves/stems break off rather than the entire seedling being pulled out of the ground. A light grazing at that stage will control the grass that will also have recovered so young sub clover seedlings are not shaded out by the competing grass. I think we need one more 20 mm rainfall event in the next 6 weeks to ensure successful establishment from this strike and this will be an excellent autumn this year for sub clover. This would be a contrast the last couple years when late autumn breaks reduced sub clovers ability to establish before it got cold. Assuming successful establishment sub clover may provide that tupping feed you are looking for so you don’t have to take the risk of mating on the lucerne.

Sub clover strike in North Canterbury (Flaxmere, Harwarden): keep an eye on it over the next 2-3 weeks to see if follow-up rains keep it alive into March – which should then mean it will survive and thrive this autumn (Photo: Sub strike at the Zino’s family farm taken by Andrew Johnson, Luisetti Seeds).
Sub clover emerging on Bonavaree farm, Marlborough: the hard grazing in January to cope with a typical Marlborough summer has opened the space for the sub to come through. Light grazing in 2-3 weeks will aim to control the grass – so lightly taking the top off once the sub has anchored. (Photo supplied by Fraser & Shelley Avery, Bonavaree, Marlborough).
Sub clover germinating after recent rain at Bonavaree, Marlborough: leave it until 3-4 clover leaves have emerged (and it has anchored itself in the ground) before light grazing. A strike this early could either 1) all die if it goes dry again (false strike) or 2) hopefully – provide 2-3 t DM/ha of quality feed by the end of April that can be grazed and then allowed to recover for spring. (Photo supplied by Fraser & Shelley Avery, Bonavaree, Marlborough).
Sub germinating on shallow stony dryland soils at Ashley Dene, Canterbury (Photos: Malcolm Smith, Dryland Pastures Research Group).