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Pasture renovation after flooding

While a speedy recovery is important don't do a rush job as they usually get poor results. Do the job once and do it properly.

Previous experiences from major flooding events (e.g. Cyclone Bola, Manawatu, Waimana) provide the following guidelines on the approach to pasture renovation.

  • Take time to clear rotting trash
  • Remove any gravel/shingle that won't provide a good seedbed
  • Plant annuals to give quick bulk of feed and undersow or regrass in the autumn.
  • Drilling usually provides better results than oversowing
  • Or use a combination of annuals and permanent pasture by direct drilling or cultivation where a substantial area of the farm has been affected
  • Fly seed on if necessary to get pastures established quickly, use pelleted seed
  • Weeds survive well, especially with spring sowing.  Have a plan for them
  • Nitrogen and Sulphate applications are critical for quick pasture establishment
  • With heavy silting phosphate and potassium may also be required

Pastures will be in a variety of damaged states from being lightly silted to being dead from having been under water for weeks. An assessment should be made, as the method used to get pasture growing again will vary depending on the type of damage. The type of pasture damage that can be expected and a summary of management practises to overcome these problems are outlined below.

Other considerations

Species: There will be a desire to get bulk feed quickly by sowing an annual ryegrass providing that perennial is undersown or regrassing carried out in the autumn.  Some of the new hybrid and perennial species will establish with similar vigour but will persist for much longer.

Establishment: Aeration of the soil is essential especially where the land has been under water for some time.  Ripping, drilling and conventional cultivation will give the best results.

Fertiliser: Much of the silt that covers your farm will have come from steeper hill country and will be of lower fertility.  Capital fertiliser may be required.   Sulphur is essential and with silting greater than 100mm additional phosphate will be required in the spring mix.

Nitrogen: Flooding causes a short-term deficit of nitrogen and sulphur in the soil. The rotting pasture also uses up nitrogen.  Apply SOA or urea with sulphur either at the time of sowing or one week after the pasture has germinated at 150kgs/ha 50% urea; 50% SOA.  Nitrogen is a key to getting pastures established and must continue to be applied at rates of 30-40kgs N/ha.

Summary of key management issues

Feed budget

  • Assess situation rating land as to the percentage of the normal productive capacity and plan the on-going stocking rate
  • Once a day (OAD) milking maybe a suitable option

Protect existing pasture

  • Do not damage existing high producing pastures, stand cows off as necessary

Regrassing

  • Aerate soil if possible
  • Sow annuals and undersow with perennials or regrass in the autumn
  • Or use a combination of annuals and permanent pasture by direct drilling or cultivation where a large area of the farm has been affected

Fertiliser

  • Nitrogen and sulphur are essential at sowing or a week after germination
  • Nitrogen on-going is critical for establishment and feed

Animal health issues

  • Stock cannot graze silty pastures too long - stops rumen function, need to mix with other feed
  • Magnesium important with cows under stress
  • Be aware of nitrate poisoning on lush new grass, especially if stock coming off older feed
  • Clean water troughs

Remember, land is a remarkably resilient resource. Time and some strategic inputs will restore the productive ability of land remarkably quickly.