On Development Of Grasslands

Press, Volume CIII, Issue 30366, 15 February 1964, Page 6

On Development Of Grasslands

A belief that aerial oversowing and topdressing is a technically superior and more economical approach to development of tussock country than cultivation methods was expressed by Dr. K. F. O’Connor, officer in charge of the Lincoln sub-station of the Grasslands Division of the Department of Scientific and Industrial Research, when he spoke to runholders attending a field day at the Department of Agriculture’s experimental area at Broken river last week-end..

During the day several references were made to the approach to land development that had been made by the Lands and Survey Department. Dr. O’Connor said that five years ago he had urged the department to follow the method of the runholder in topdressing and oversowing from the air on such country as Te Anau rather than spending large sums of money on mechanical clearing and cultivation. He described the conventional aproach with cultivation and mechanical methods of land clearing as both economically and biologically unnecessary and often ineffective. Of vital importance to runholders in making decisions about management of their country was what he called “the grassland development transition,” or the build-up of the soil to a higher level of fertility and at the same time attainment of some sort of parallel increased productivity. This grassland development transition was the second phase ■ of grassland husbandry. There would not be much gain, he suggested, in consideration of the first phase, the management and utilisation of natural or unimproved grassland. On country like the terraces at Broken river, he said runholders would be able to see for themselves that sheep were rarely on it. This browntop sweet vernal association producing 30 to 1001 b of dry matter to the acre was carrying something like one sheep to 30 or 40 acres. The sheep were actually being carried on sloughs, wet places and little washes

where production was of the order of about 20001 b of dry matter to the acre and where carrying capacity was about two sheep to the acre, so that these small but significant areas were no longer unimproved and were being improved by the sheep themselves. . Dr. O’Connor said in work Which he had initated close to this experimental area on Enys Flat in 1957 he had ■sought to study the effect of ground preparation on establishment and growth of legumes and grasses. Some people who were disappointed with aerial oversowing and topdressing might be tempted to say “let us use the plough and grow good vega-. tation” But between Springfield and Broken river were paddocks of sweet vernaland browntop that had been ploughed twice since he. had been working in the area. In a good season cultivation could be followed .by a good establishment of cocksfoot or ryegrass, and in a dry season drilling had to be practised as establishment by broadcasting was not satisfactory. Cultivation reduced the need for fertilisers for establishment, but no matter what the ground preparation, an over-riding factor for growth and. production of these sown grasses had been the marked response to sulphur, phosphorous and nitrogen.

With the all-important clovers needed for fertility building, he said there was no gross gain from cultivaton in getting establishment or density of plants. Once satisfactory fertiliser

was applied and sowing was well timed, broadcasting of. clovers.gave sufficiently good establishment for the development of good production As was the case with the grass, no matter What the ground preparation was, it Was fertiliser quality and quantity which governed the actual yeld of legumes. Dr. .O’Connor said evidence of the Department of Agriculture pointed to broadcasting being more effective than drilling in farm practice because it could be done in mid-winter, whereas drilling could not be attempted until the spring.

Dr. O’Connor also referred to another study on the effect of liming on the growth of grasses such as cocksfoot and ryegrass. At every level of application of superphosphate and nitrogen as urea there had been a response in the trials to two tons of lime. This had occurred at Broken River with a pH of 5.4 and also at Pukaki on a soil with a pH of 6.1. Lime Effect The effect of the lime, he said, was to activate nitrifying bacteria in the soil so that conversion of ammonium nitrogen to nitrate nitrogen was increased. This had been shown at Enys Flat in the Broken river area by Dr. J. Robinson, a Canadian, who had studied the bacteriology of this soil while working for a doctorate of philosophy at Lincoln College. It appeared that this conversion to nitrate nigrogen was of great importance to ryegrass and cocksfoot which apparently required some of their nitrogen in the form of nitrate. In contrast, browntop ana sweet vernal were apparently able to thrive when only ammonium nitrogen was available in quantity.. There was also a factor that ryegrasses and cocksfoot were grasses with a relatively high cation exchange capacity on their roots in comparison with sweet vernal and browntop which had low cation exchange capacity. This meant that cocksfoot and ryegrass were poor competitors for cations such as ammonium

and potassium and they were also poor competitors for aniens such as sulphate and phosphate. For any grass to take up ammonium cation a good supply of anions, generally sulphate or phosphate, or both, had to be present so that plants that were poor competitors for sulphate and phosphate apparently required higher applied levels of phosphate and sulphate in order to respond to ammonium nitrogen. The sum of all these features was that if a sweet vernal and browntop legume system was replaced by a ryegrass and cocksfoot system this was almost certainly going to demand higher levels of lime, and probably higher levels of' sulphur and phosphate, though the increase in the latter was probably not so significant as they were already needed by legumes which were least able to compete for them. Since the costs of mechanical cultivation and lime transport were relatively high, Dr. O’Connor suggested that use of aerial topdressing and oversowing was probably more economical than increasing expenditure on lime and mechanical cultivation equipment.

Current experiments by Mr A. J, Harris at the Grasslands sub-station at Gore were also showing that fat lamb production on a browntop-white clover -association under high fertility and close grazing was as good as from white clover and ryegrass. However; Dr. O’Connor said, sweet vernal and browntop had limits to seasonal production, and f°r late winter or early spring production

legume-rich swards of lucerne or clovers might be overdrilled. Rather than introduce ryegrass and cocksfoot in this Way to raise production in low lime areas, he proposed that it might, be desirable to use such low cation exchange capacity plants as wheat, oats and barley. Reviewing the results of several grazing and fertiliser management experiments he had carried out in the Mackenzie basin from Tara Hills to Pukaki, Dr. O’Connor said that where bard grazing was practised production had been superior in the following spring, especially in the grasses.

Thus where a pasture was strong in clover and it was hard grazed, the effect of putting it through the animal was to convert nitrogen to a form more readily available to grasses and at the same time to be making money out of the animals. It also opened swards for entry of sown or volunteer grasses. The obvious need for an effective grassland development transition was sheep and more sheep. Discussing the position at Broken river where, following cultivation there was apparently a need for more fertiliser, Dr. O’Connor said that there was a build-up in nature of organic matter on the surface which could absorb phosphate like a sponge absorbs water. In natural conditions this sponge was already partially filled. When soil was turned over this sponge was lost and the process had to start again building the organic layer and filling it with relatively unavailable phosphate.

Summarising, Dr. O’Connor said the existing grasses in this country were highly productive in season if they were well fed. If they were cultivated there was temporary loss of their production and the farmer was likely to have to face a bill for lime, seed, freight, and for- mechanical equipment and its operation.

It could be, he added, that this situation was widespread on acid soils that had had no previous development. If the liming effect on grasses was of wide significance, it was another example of how work in the tussock grasslands could be of much wider significance for New Zealand as, for example, early work on sulphur and work on the inoculation of legumes. In discussion, Dr. O’Connor said that if the private runholder had been more successful in concentrating on aerial topdressing, the State had been superior in the way that it had utilised the feed that it had grown. The prime sin of the runholder had been in not utilising feed. Mr L. W. McCaskill, the Director of the Tussock Grasslands and Mountain Lands Institute, said he could not help feeling that more areas could have benefited not only from more fertiliser but also more sheep at the right time.