Establishment, management on over-sown high country

Press, 12 July 1985, Page 25

Establishment, management on over-sown high country

Opinion is divided on the wisdom of including grass seed in the seed mixtures for initial oversowing of tussock grasslands in the South Island hill and high country. “Most farmers do it, but the proportion of seed that establishes is generally very low,” according to a D.S.I.R. scientist, Dr David Scott, of the Grasslands Division at Lincoln. Consideration should be given to leaving the grass introduction to several years later, he said, though there was no data to suggest it was any easier then.

Where sites could be fully cultivated and drilled then seeding mixtures and rates need be no different in the hill and high country than elsewhere.

Initial aerial oversowing of tussock blocks should be based on clover with 4 to 6 kg a ha of inoculated coated seed. Evidence was somewhat divided as to composition with a common compromise being alsike, white clover, and red clover in equal quantities. Where higher fertiliser rates were used and subdivision for subsequent grazing control was good then a higher proportion of white clover could be used. However, there was good evidence, at least in the high country, that many of the reported collapses of oversowings after a number of years were related to excessive build up of white clover material which was toxic to itself and other species, although lack of maintenance fertiliser, and inadequate grazing management were the more common causes. Alsike clover was more suitable for large areas with moderate fertility input which might not get desirable subsequent management.'

Red clover always established, but was generally less than its sown proportion in the established pasture. Lotuses should be sown alone as they were weakly competitive at the establishment stage. The first requirement of any site preparation should be fencing to ensure grazing management. To overstate the case, said Dr Scott, paddocks for development could never be

too small. Paddocks should never be more than 50 ha and sizes of five to 20 ha, or one week’s grazing, would be desirable. Where there was dense resident vegetation, competition should be reduced prior to sowing.

This could be done by grazing, and again if there was prior subdivision fencing into small blocks, then the duration that stock need to be kept on a block to clean it up should not be to the detriment of the stock. The grazing option required planning at least a year in advance of sowing. Other options were burning or costly herbicide. Opinions differed on the preparation of more open resident vegetation, he said. In the high country it had been established that bare ground was a less favourable seed bed for surface sown seed than vegetation. Opinions differed as to whether some cover should be left as shelter for seedlings as compared with its competitive effect. A rough guide would be for short ground cover of 35 cm to occupy 50 to 70 per cent of the area to be oversown.

Drilling was nearly always superior to broadcast surface sowing, particularly so in the drier areas. Throughout most of the high country only spring sowings (mid Septembermid October) should be considered, because of very variable autumn rainfall for growth and establishment, with the additional hazard of loss by winter frost. In the lower dry high country and throughout hill country opinion was somewhat divided on an autumn versus spring sowing, but this probably should be seen as a transition towards the common autumn sowing in

the higher temperature lowlands. There was a general under-estimation of the time pasture needed to be left to establish itself before use. In the high country, this should be a full growing season, and may be several years, on harder sites.

Plants should be allowed to grow to at least 5 cm and preferably 20 to 30 cm in height before grazing. Most initial oversowing or overdrillings of high country tussock country would become extremely clover dominant, and periodic brief, hard grazing would be necessary to encourage root development of any sown grasses.

Grasses might take several years to become obvious.

Inoculation of legume seed was essential throughout the high country, with the only possible exception being for white, red and alsike clover into areas that already had a high population of haresfoot clover. Sowing legumes without rhizobia inoculation was a waste of money. Lucerne should. be inoculated even when resowing into areas which previously had lucerne — and it should never be immediately after a previous lucerne crop. It is doubtful whether individual farmers could consistently inoculate and pellet legume seed, and even commercial seed coating firms with good quality control had occasional failures, Dr Scott said.

Subdivision was the key to the development of hill and high country properties as it was elsewhere in New Zealand. There was a preference for associating this subdivision with the concepts of “special purpose” paddocks rather than with “rotational

grazing.” The important principle in management was not the pastures were grazed in regular sequence but rather that they were grazed intensively for a short period (with a week being a compromise between pasture management and animal considerations) and the pasture allowed to regrow uninterrupted until the next grazing. The caution was that this required period of regrowth might differ widely between pastures on different sites, so that paddocks might not be grazed in the same order in different periods of years.

“These differences in desirable regrowth might be very large in the hill and high country, though we have not considered spelling periods of one or more years as is done in some parts of the world,” he said. “The term ‘special purpose’ paddock conveys the desirable concept of each area or paddock being managed to fulfil feed requirements at one stage of the year.

“On many better sites, the same area could fulfil feed requirements at many times during the year.” When stocked, paddocks should have sufficient animals to achieve utilisation of 60 per cent or better in a period of no more than 10 days. Some hill and high country properties were already achieving the more desirable shift of two to three day It may take three to four years of fertiliser and intensive grazing plus adequate regrowth spelling to achieve the full potential of development. “But increases of five to eight fold in production could be expected,” said Dr Scott.