Hints on dealing with browntop

Waimarino Bulletin, Volume 2, Issue 37, 5 March 1985, Page 6

Hints on dealing with browntop

Many factors contribute to the development of largely browntop dominant pastures, and the following 'hints' on dealing with the problem have been supplied to the Bulletin for the benefit of Ruapehu region farmers. Browntop is inherently better than ryegrass at competing for phosphate, and, with the very high phosphate retention of the soils of the central plateau, any short fall in fertilizer application very quickly mpans only the most competitive species survive. While ryegrass will compete with browntop and is quite capable of dominating it, it needs a good supply of nitrogen to do this. With winters often in excess of 150 days, the period of the year which clovers are actively fixing nitrogen is not very long so that nitrogen inputs are not potentially as great as in warmer areas. Nevertheless the clovers do fix some nitrogen and by encouraging the cycling of this nitrogen by rotational

grazing, the ryegrasses that are present will respond. . Pasture improvement can be achieved by rotational grazing and especially by heavy grazing in winter, but this process is relatively slow and to be really effective only a small area can be tackled each year due to the constraints of flushing and tupping at one end and lambing at the other. So, while this process will continue as it is a relatively inexpensive development tool, other ways must be looked at if they can speed up the process and are economically viable. The oldest method of renewing pastures is probably by ploughing and putting in a spring sown brassica crop, then putting down permanent pasture either when that or a second crop is finished. This system has a whole set of limitations in terms of pasture improvement. What is required by farmers developing browntop is a system which can rapidly convert browntop pastures to ryegrass pastures when the season and finances (either from income or borrowed) allow, and do this at a cost which is recouped from increased production in as short a time as possible. The system now referred to as Conservation Tillage, or C.T. for short, achieves this objective as well as adding a number of other benefits. C.T. for pasture renovation basically consists of killing the existing vegetation using a herbicide, followed by direct drilling of

new species. It is a simple and reliable technique provided some basic guidelines are followed. Development of browntop pastures by C.T. has really only been possible since the discovery and development of Roundup herbicide which, because of its ability to translocate through the plant, destroys the root rhizomes of the browntop as well as killing the top growth.

The action of killing the root systems speeds up the breakdown of the browntop turf mat so that a lengthy fallow period is not required and you no longer have to put in a forage crop to assist breakdown. Pasture renovation by C.T. can begin in the spring as soon as the temperatures have warmed enough to start the browntop actively growing and can continue right through until mid-late autumn.