High Country Tussock Grassland Improvement in Canterbury

New Zealand Journal of Agriculture, Volume 91, Issue 6, 15 December 1955, Page 554

High Country Tussock Grassland Improvement in Canterbury

By

A. R. DINGWALL,

Assistant Fields Superintendent, Department of Agriculture, Christchurch “THERE is a growing interest in the possibilities of improving high country tussock ’ grasslands by the introduction of clovers accompanied by topdressing. This article gives results of a trial on ploughable tussock country in Canterbury.

'T’HE plant communities of these sub-alpine regions, dominated in their virgin state by hard tussock (Festuca novae-zelandiae) or silver tussock (Poa caespitosa), have always been naturally devoid of leguminous plants, except for the. relatively sparse population of native brooms (Carmichaelia spp). During a century of farming occupation many of these areas have become strongly invaded by aggressive but low-producing exotic grasses such as browntop (Agrostis tenuis') and sweet vernal (Anthoxanthum odoratum), to the detriment both of the original vegetation and the carrying capacity of the high country runs. The moderately acid soils of these natural grasslands are inherently low in phosphate and available calcium and nitrogen. In some instances they have also proved deficient in other essential plant nutrients such as sulphur and molybdenum. Thus on unimproved high country swards drymatter production is limited and the herbage produced is seasonally deficient in proteins and certain essential minerals, deficiencies that could be overcome largely by the inclusion of leguminous plants. Introducing Legumes Aerial oversowing or the employment of grassland coulter tips for sub-

surface drilling of seeds and fertiliser offer practical means of introducing legumes over vast areas of tussock grassland swards without an immediate disturbance of the existing vegetative cover. The transformation accompanying the establishment of clovers under such conditions is shown in the upper left illustration on page 553. Though the sowing of clovers in tussock grasslands is by no means a recent practice, the full significance of introducing legumes into these environments has yet to be determined. Opinions may differ as to the eventual outcome of establishing high-fertility-demanding legumes in subalpine tussock communities, but it is generally conceded that their introduction can result in an early improvement in carrying capacity on the sown areas. It is also considered that such introductions, together with the more concentrated grazing afforded, should in time lead to build-up of soil fertility on improved areas. If this desirable result accrues, subsequent establishment of palatable and productive grass species into tussock grasslands may be greatly facilitated. Difficulties with Grasses Whereas experiments and farming practice have shown that clovers can be readily introduced into most hard

tussock and silver tussock areas, useful grasses are not nearly so readily established in the initial stages of improvement. Under certain circumstances, especially on the better-class silver tussock country under favourable rainfall, grasses such as cocksfoot (Dactylis glomerata) and tall oat grass (Arrhenatherum elatius) can often be established with the original sowing. Nevertheless, failing some form of surface cultivation the successful introduction of productive grass species into most of . the high country tussock grasslands, particularly where hard (fescue) tussock forms or formed the dominant constituent, must await a period of clover growth and grazings. High Country Trials As part, of the programme of tussock grassland research a trial was .begun in November 1953 in the Broken River area, “Flock Hill” Station, within the watershed of the upper Waimakariri River. The trial is on ploughablecountry at an altitude of approximately 2400 ft. in the 45in. rainfall belt. The natural vegetative cover (see upper left illustration on page 553) consists of unthrifty hard and blue (JPoa colensoi) tussocks with stunted matagouri (Discaria toumatou) and tauhinu (Cassinia fulvida), strongly invaded by browntop, sweet vernal, and Yorkshire fog (Holcus lanatus). Methods of Seeding The main object of the trial was to determine the comparative effectiveness of three methods of seeding for establishing grasses and clovers in tussock swards.

The three methods were: Subsurface drilling of seed and fertiliser with grassland tips; orthodox broadcasting of seed and fertiliser on an undisturbed surface, as in ordinary and aerial oversowing; and surface broadcasting on a surface disturbed by pitchpole harrowing. The first two methods retain the natural ground cover, but in the third method much of the existing tussock is uprooted, the extent of the disturbance depending largely on the severity of the. pitchpoling and the original density and type of vegetation. Pitchpole harrowing also gives a certain amount of tilth to allow better seed coverage (which is improved by rolling after sowing) and reduces plant competition in the early stages of establishment of seedlings from sown seed. The seeds mixture sown (at 211 b. per acre) in this trial included perennial ryegrass (Lolium perenne), cocksfoot, alsike (Trifolium hybridum), Montgomery red clover (Trifolium pratense), and white clover (Trifolium repens'). The comparative' results from ■ the three seeding methods, as seen in January 1955, the second season after sowing, are shown in the upper right, middle left, and middle right illustrations on page 553. Clover establishment . and growth where subsurface introduction of seed was made by grassland tip drilling has given virtually a complete ground cover of legumes. The same degree of cover has not yet been achieved by either of the other two methods, even though they are by no means unsatisfactory. During the early stages of establishment and through the first season,

when the plots were subject to continuous and moderately severe grazing, the difference between the drilled and surface-sown areas was even more marked. Differences in clover establishment and growth on the ordinary broadcast and pitchpoled areas have never been so distinctly marked, any difference being in favour of pitchpoling. Pitchpoling has, however, encouraged the establishment of cocksfoot plants, which are not as yet noticeable in the drilled or broadcast sections. Figures for dry-matter herbage production during the second season (from September 1954 to April 1955) confirm observations of response differences and relative merits for clover establishment. These figures are given in Table 1. TABLE I—DRY-MATTER PRODUCTION IN METHOD OF SEEDING TRIAL (September 1954 to April 1955) Method of Dry-matter Relative seeding production production lb. per acre Drilled . . . . 3,507 200 Pitchpoled . . 1,806 102 Broadcast .. 1,770 100 Response to Fertilisers Soil tests of the area taken at the start of the experiment gave the following analytical results: pH, 5.6; available calcium, 2; phosphorus (P 2 O 5 ), 1; potash, 8; and molybdenum, 0.08 p.p.m. With such tests responses to lime, phosphates, and molybdenum are to be expected. A base dressing of superphosphate at licwt. per acre was used for all plots and cross treatments of lime at lOcwt. per acre and sodium molybdate at 2|oz. per acre were added. The layout gave fertiliser treatments of superphosphate alone, phosphate plus lime, and phosphate plus molybdenum. The results achieved and also as observed during the second season are shown in the upper right, lower left, and lower right illustrations on page 553. In the establishment and initial season’s growth the superphosphate plots proved very disappointing, even on a section of the trial where this fertiliser was used at up to 6cwt. per acre at the time of sowing. Seedling establishment was relatively sparse and initial growth showed distinct chlorosis (loss of colour) of leafage. A good strike and early response were obtained with phosphate plus lime, but by far the most outstanding response, as indicated by density of strike, growth vigour, and colour of herbage was achieved with phosphate plus molybdenum. Throughout the second season the sections treated with superphosphate and with phosphate plus lime have shown marked improvement. Toward the end of the second season ground cover of clovers

on the limed plots appeared little inferior to and growth equal to, if not better than, that on the molybdenum plots. The limed plots had received a further dressing of lOcwt. of lime — making a total of 1 ton per —and all plots received a second application of superphosphate at lcwt. per acre in August 1954. The initial molybdenum application of 2Joz. per acre has not yet been repeated. Herbage production resulting from the various manurial treatments during the period September 1954 to April 1955 is indicated in Table 2. TABLE 2—*DRY-MATTER PRODUCTION AND MANORIAL TREATMENTS (September 1954 to April 1955) Fertiliser Dry-matter Relative applied production production lb. per acre Superphosphate ■ .. 2,415 100 Super. + lime .. 3,217 133 Super. + molybdenum 3,796 157 * Production on plots drilled with grassland tips. Conclusion Evidence from this trial indicates that red clover, alsike, and white clover can be readily established in fescue tussock high country by the three seeding methods employed, but that subsurface drilling with grassland tips gives a much more even strike and better herbage production in the first two seasons than either broadcasting on an undisturbed surface or after pitchpole harrowing. On the other hand the inclusion of grass species, perennial ryegrass and cocksfoot, in the initial oversowing does not appear warranted unless some form of prior surface cultivation such as pitchpole harrowing is adopted or the existing cover is naturally open. This is especially so where the tussock grassland is already strongly invaded by such aggressive exotics as browntop, creeping fog (Holcus mollis), sweet vernal, and Yorkshire fog. Though in this trial the results from superphosphate have not been encouraging, experiments and farming practice in some other localities throughout the high country of Canterbury have shown that there are areas where phosphate alone will give immediate and successful results. Similarly, it has been shown that sulphur, which occurs as the calcium sulphate impurity of superphosphate, may play as important a part as the phosphorus fraction of superphosphate in the establishment of clovers in certain tussock areas. However, successful early establishment of clovers in the hard (fescue) tussock grasslands of the upper Waimakariri River watershed would appear to depend on the use of lime (preferably applied 6 to 12 months in advance of seeding) and/or molybdenum in addition to phosphate fertilisers.