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Coastal pasture transitioning

The predicted El Nino that loomed at the end of 2015 was not looking favorable; hot, dry and potentially very desperate. Then the rain began to fall in early January, with some areas receiving double their January average rainfall. Temperatures remained mild with high humidity; providing perfect conditions for summer growing species particularly kikuyu. In a monitoring program conducted locally on a dairy farm some years ago, actual growth rates were recorded at 100kg/DM/ha/day, imagine what growth rates may have been recorded this year. Coincidently this year’s abundance of feed sits alongside high cattle prices making pasture management options limited. As a result landowners are now asking how to manage large pasture yields and how to prepare for autumn/winter feed.

If we look at pasture management options this year, buying extra mouths to keep pastures under control may not be a financially viable option, but conserving surplus pasture growth is a real possibility. Just remember the quality of the bale will never be better than the fresh standing feed. It is essential to assess the stage of growth when pasture is to be cut and think about which class of livestock you intend to feed it to. This will help determine possible weight gain or maintenance outcomes in the livestock.

The third option is to use the mouths you have on hand and sacrifice a proportion of your property while setting up the remaining area for temperate species.

Concentrating on managing a smaller area will provide higher quality feed ensuring any pre-existing or newly sown ryegrass and/or clover plants receive direct sunlight stimulating germination and limiting competition while growing.

A technique described by Fulkerson and Reeves in 1996 still holds true today. The technique recognises the critical importance of timing in relation to soil temperature and light penetration to clover. Success relies on the removal of the kikuyu sward by heavy grazing, forage harvesting or, as a last resort, mulching after the previous grazing and allowing the mat to decompose. Herbicides provide a variable suppression and merely stop growth but do not remove the “shade”. The timing of sowing in the establishment year, or initiating management to favour white clover over kikuyu, is important. If this is begun too early, kikuyu is difficult to suppress, but if too late low temperatures will suppress the clover - a soil temperature (at 10 cm) of approximately 19°C seems optimal for an effective outcome (Fulkerson and Reeves, 1996).

More recently the NSW Department of Primary Industries Primefact ‘Milk production from kikuyu grass bassed pastures’ describes these options in greater detail. Such that:

  1. Graze, sow and then “hard” mulch. Hard mulching means a residue height of less than 2 cm with some soil exposed. Problems can arise if there is too much residue left after grazing which may restrict light and smother the emerging ryegrass seedlings.
  2. Hard mulching after the second last grazing before sowing and then again at sowing is also common. With this method it is mainly the leaf that is removed at the last mulching, having a minor effect on setting back kikuyu growth.
  3. Mulch at the third last grazing, that is 2 grazings before the ryegrass is sown (a preferable method). This allows time (usually 28 days) for the mulched mat to break down and more stem to grow. More stem and so growing points are removed at the mulching prior to sowing. This will suppress the kikuyu growth for a longer time.
  4. Application of desiccants, such as a Paraquat based chemical usually sets kikuyu growth back for 2-3 weeks. Glyphosate can also be used to set back kikuyu growth. (However, if glyphosate is used repeatedly, the kikuyu may not recover over summer allowing less productive grasses such as couch grass to take over. Therefore avoid unnecessary use of high rates and repeated use of glyphosate on the same fields).
  5. Make kikuyu silage. Hard mulch, then lock up the kikuyu for 4-5 weeks before taking a silage cut. As day length is shortening Kikuyu silage might now be opportunistic and made from a true growth surplus. Hard mulching sets back kikuyu growth for 2-3 weeks because the stem grows well during lockup and the silage harvest then removes the growing points on the stem. Sow ryegrass as soon as possible after the silage is removed.

In both articles the authors describe the optimal time to start sowing ryegrass into kikuyu pastures is when the minimum air temperature has fallen below 15°C. At this time the soil is still warm enough to get good establishment and growth of ryegrass but close enough to the onset of colder weather to restrict competition from kikuyu. Below is a graph from the Bureau of Meteorology that illustrates the mean minimum temperatures at the RAN Air Station, Nowra.


Figure 1: Long-term monthly mean minimum temperature, Nowra Air station 2000-2016.

Figure 1 depicts March onwards as being the ideal time to begin sowing or allowing for temperate species to start germinating and growing. However, this graph doesn’t show rainfall and in the last 10 years Shoalhaven/Illawarra autumns have been very variable making for a tough decision as to when to begin controlling summer growing species or when to sow a new pasture.

Figure 2 contains a lot of detail but it highlights strongly the variability experienced over the last 10 years. However despite the variability by looking at rainfall and the mean minimum temperatures together March is still the time to concentrate on making the pasture environment conducive for temperate species; but what is interesting to note is that the rainfall drops away as we move into winter. So if you miss March and start pasture management in late, April or even May it is likely that the first limitation to the temperate pasture species will be rainfall resulting in a delay of winter feed availability often until early spring. Conversely, sowing prior to these optimum times can be desirable to produce early winter grazing, but it requires an aggressive management strategy to suppress the growth of kikuyu.


Figure 2: Rainfall (mm) measured at the Nowra Boat shed over the last 10 years from 2007-2016

In conclusion, for the February to April 2016 period the Bureau of Meteorology has predicted a 55-60% chance of exceeding median rainfall in the Shoalhaven/Illawarra and temperatures at a 50 % chance of exceeding medium maximum temperatures. With this information now is the time to start taking back control of this seasons abundant kikuyu growth to ensure temperate species are not competing for sunlight. Proactive action will be critical in setting these pastures up to be high quality temperate species based pasture swards.

References:

Further information:

Amanda Britton
Senior Land Services Officer - Pastures
Amanda.Britton@lls.nsw.gov.au