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pastoral development
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Tussock Grasslands MIS
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pastoral development
web paper |
Bill Lowther
AgResearch, Invermay Agricultural Centre, Mosgiel.
Development of tussock grassland by oversowing and topdressing is often done where it is cheapest and easiest, rather than where most needed. To achieve maximum return on farm investment it is essential to research land resources and define feed limitations, before proceeding with seed and fertiliser. [A full discussion on pastoral development is given in Guide to Tussock Grassland Farming edited by Mike Floate (1992)].
A benefit of the development of a portion of the property by the addition of nutrients and the sowing of introduced plant species is likely to be a reduction in grazing pressure on the undeveloped portions of the properties and thus on the indigenous species they support. Continued sustainability of the indigenous species on these areas is seen as an objective almost as important as the provision of more and better feed on the developed areas.
Introduced pasture species are used to improve the quality and the quantity of feed grown for domestic stock. However, matching the increased feed supply to annual stock demands is difficult in an environment characterised by long winters, unpredictable climate and rugged terrain. Every high country run faces a different set of problems and, because of this, no set recipe can be given. The main thing is to know how to approach development and how to get the most from it.
First, build a property plan that includes all resources. Map in detail soil type, aspect and steepness of terrain. This is important, because flats and sunny and shady faces all have different productive potentials, different fertiliser requirements, and vastly different management requirements. Part of the resource plan should include location and continuity of supply of natural water, potential for irrigation dams and future stock water, and location of tracks for both stock and vehicles. When defining limitations it is necessary to look at what is holding back development. It could be a summer or winter feed deficit, acid soils, lack of rainfall, poor access, lack of subdivision, or simply poor management. For instance, if a property is suffering a winter feed deficit, then development in some areas such as shady aspects will only aggravate the situation. Alternatively, if a summer shortage is the problem, irrigation on flats, or oversowing some higher and wetter country must be considered.
Site preparation: Dense vigorous vegetation can reduce both germination and survival of seedlings. If such country is to be oversown, natural roughage should be cleared either by using large mobs of sheep or cattle or, if necessary, burning. However, complete removal of cover can result in poor establishment, particularly on dry sunny faces. Here burning should be contemplated in the season prior to oversowing.
Time to oversow: The best time to oversow varies from early August on low sunny faces to late September on higher shady faces. Later oversowing is not advised, because early onset of dry conditions can seriously reduce establishment.
If grass seed is applied later in the development programme, careful grazing is necessary to reduce competition during establishment.
Inoculation and pelleting: [Inoculation and pelleting of legume seed AgFact No. 35. Bill Lowther and Heather Pryor 1997] Inoculation of seed can be essential because the rhizobia that nodulate clover, lucerne, and lotus are absent from most areas of tussock grassland. It is only where haresfoot clover is abundant that satisfactory populations of clover rhizobia are guaranteed, and inoculation is not essential for clover, but it is still needed for lotus or lucerne. However, if in doubt, inoculate, because compared to overall costs it is a cheap insurance.
Pelleting of inoculated clover and lucerne seed can enhance survival of rhizobia on the seed both before and after oversowing. It is most effective when oversowing in conditions marginal for rhizobia survival and seedling nodulation, such as those on dry sunny faces, bare soil surfaces, and acid soils.
In contrast to clover and lucerne, Grasslands Maku (Lotus pedunculatus) has shown little response to seed pelleting. The present recommendation is to slurry-inoculate the seed using up to five times the manufacturer’s recommended rate of peat inoculant.
On molybdenum deficient soils the addition of molybdenum to the seed coat ensures an immediate supply to all seedlings. Molybdenum deficiency is most likely on the moister yellow-grey earth (YGE) soils (now called pallic soils) with a mean annual rainfall in excess of 600 mm, and in yellow brown earth (YBE) soils (now called brown soils) [see also Guide to Tussock Grassland Farming edited by Mike Floate (1992)]. Similarly, sulphur-containing pellets are recommended for use on sulphur deficient soils, although sulphur fertilisers are still required. The soils of the driest environments brown-grey earth (BGE) soils (now called semi-arid soils) and pallic soils with less than 600 mm mean annual rainfall are likely to be the most sulphur deficient.
Coating of grass seed may increase establishment of oversown grass in some cases through improved germination. However, advantage remains doubtful as results are highly inconsistent and depend on both site and season.
Fertiliser: Fertiliser recommendations for pasture establishment vary with the soil type. The moister high country YBE soils are more acid and are likely to be deficient in sulphur, phosphorus, and molybdenum. Molybdenum-superphosphate fertiliser applied at 250 kg/ha at sowing should be sufficient for 2-3 years. On YGE soils (greater S deficiency and less P deficiency) 185 kg/ha of molybdenum-sulphur superphosphate (28%S) should be sufficient for 2-3 years. On BGE soils (S deficiency) 185 kg/ha of molybdenum-sulphur superphosphate (28%S) should again be sufficient for 2-3 years. Lime (1 tonne/ha) could be applied at sowing on the YBE soils if the returns can be shown to be economic [see also Guide to Tussock Grassland Farming edited by Mike Floate (1992)].
Grazing management during establishment: The use of large mobs of stock to trample seed into the soil immediately following oversowing can greatly improve seedling establishment. This is especially true for denuded semi-arid areas, where dry conditions for short periods can prevent germination. However, for this practice to be successful, subdivision fences must be planned and erected before oversowing.
Seedling growth is generally slow, depending on location, climate, and species oversown. Grazing should be deferred until seedlings are well established, which in most environments may not be until the autumn following sowing. Dense grass swards such as browntop are an exception. Here strategic grazing during the establishment year is advised to reduce competition from the existing grass sward.
Grazing of Maku lotus must be avoided during the establishment year, because seedling growth is very slow. Following this first year, careful grazing of Maku is necessary to encourage plant spread. Such spread of Maku results mainly from autumn growth of underground rhizomes, and grazing over January-March restricts this spread.
Apply only the minimum fertiliser necessary for a block or landscape, depending on soil requirements and intended utilisation. Careful soil sampling is advised, to obtain specific recommendations for initial (i.e., establishment fertiliser – see above) and maintenance fertiliser rates.
Maintenance fertiliser: Fertiliser applied to maintain pasture production is determined as equal to the nutrients lost from the system by the sale of sheep meat, live sheep, and wool, and nutrient redistribution by animals, together with losses of nutrients by leaching and fixation in the soil. Replacement of nutrient losses does not have to be annually but can be done at 2-3 year intervals on a given block of land. High-analysis, slow release materials are especially suitable because they allow savings on the bulk of fertiliser to be transported and applied and reduce the frequency of application. Maxi sulphur superphosphate (50% S) is (e.g. 100 kg/ha provides 50 kg S/ha for 2-3 years) is an ideal high analysis fertiliser for the dry sulphur deficient soils. For moister soils (see above), which are both sulphur and phosphorus deficient, maxi sulphur super may be mixed with high analysis phosphorus fertilisers such as reactive phosphate rock. Commercial companies prepare these and other specialist mixtures such as "Longlife Super" and "Tussock" fertiliser brands. A model for calculating high country pasture fertiliser requirements ("Overseer") is currently (January, 2002) being upgraded and will be available for all commercial fertiliser recommendations, and for planning purposes. The rates of different nutrients for maintenance vary with the intensity of grazing and/or whether the pasture is cut for hay. Typically oversown tussock grassland blocks support 1 to 3 stock units/ha/year, so maintenance fertiliser S could range between 3 and 9 kg S/ha/year, and, where required, fertiliser P 2 to 6 kg P/ha/year.
Often fencing is not given enough priority in a development programme. However they are essential for sustainable management of the pastures and the efficient conversion of feed into animal products.
The type of fencing is not important, so long as it is effective. However, for cheapest subdivision of difficult terrain, electric fences and solar panels should be considered. Appreciation of aspect is very important when planning subdivision, particularly where improved sunny blocks are the main winter feed source.
The winter feed deficit is likely to remain the major problem, and in some areas early spring and mid-summer may also be pinch periods. Sunny faces up to mid-altitude levels (900 m) can be utilised throughout winter, because snow risk here is less than on the flats. These sunny faces also make excellent lambing blocks, provided there is some relief from grazing in early spring. Subdivision is needed on sunny faces for budgeting winter feed, even spread of ewes during lambing, and mobbing up for rotational grazing following marking.
Shady faces should be utilised during the growing season. The warmer of these are best for lambing and mating, while those colder or higher shady faces provide good summer pasture for young stock. Here clovers are of major importance.
Species [A guide to pastures and pasture species for the New Zealand High Country Scott et al 1995; Guide to tussock grassland farming edited by Mike Floate 1992]
The main species in high country pasture mixes are white, alsike and red clovers. However, under the higher levels of utilisation recommended contribution from red clover is often insignificant after the first year. Alsike will contribute most initially, but as its growth form is closer to that of red, it will not persist as well as white clover. Development of the lower altitude sunny faces and elevated fans can provide valuable early spring feed, giving some relief to the lambing blocks. Lucerne should be oversown or direct drilled here on runs with less than 600 mm rainfall, because white clover will not persist. Irrigated grass/clover, red clover, or lucerne on the flats will alleviate the summer dry problem.
Maku lotus oversown on higher altitude sunny faces (up to 1500 m) can alleviate feed shortages during the summer dry period. Here soils are less fertile, but temperature rather than moisture is limiting. An advantage from this is that, in very dry summers, temperatures are generally warmer, ensuring even greater lotus production.
Opinions differ over whether grass seed should be included in the initial oversowing mixture. Because of the low nitrogen status of tussock grassland soils, grasses make little contribution to dry matter production in the early years. The important point here is not when to oversow grasses, but that at some stage they should be oversown, particularly on wintering blocks. Cocksfoot will respond to moderate grazing levels, provided frequent spelling is allowed. In contrast, ryegrass is more suited to higher grazing pressures, but may not be as productive in dry summers, and will not withstand severe winter conditions on cold shady faces above 750 m altitude.
Grazing management [Successful high country grazing management Bruce Allan 1997]
The key to successful management of improved tussock country, as for cultivated lowland, is controlled utilisation. Control prevents both loss of introduced species through overgrazing and loss of pasture quality through undergrazing. Stock numbers must be increased in accordance with increased pasture production, and fencing must be carefully planned to facilitate easy but flexible management. Rotational grazing improves the evenness of utilisation within blocks and creates a feed bank ahead of stock, thereby helping annual feed supply to meet annual feed demand. As a guideline, blocks should be small enough to allow mobs to achieve 60-70% inter-tussock utilisation within a 7-10 day grazing period. There should be sufficient blocks within any rotation to allow at least 3-4 weeks regrowth. In most cases at least 30 hill blocks are needed to operate an effective management system. More blocks mean greater flexibility and control. Following lambing, a grazing density of 50 SU/ha is a desirable goal, but in many areas, remoteness, terrain, and lack of stock water will make achievement of this difficult.
In areas that are on average dry (e.g. < 650 mm rainfall) controlled utilisation of pasture may not be practical during occasional years with moist growing seasons. Stock numbers are geared to the production that occurs in ‘average’ years, so that when pasture growth is enhanced by the moist season it is excess to animal needs. In these circumstances a degree of controlled utilisation of improved pasture is possible by prolonging their grazing and spelling unimproved tussock grassland. In addition undergrazing in one year may be corrected in the subsequent year.
Allan, Bruce. Successful high country grazing management. Meat Research and Development Council, Wellington.
Lowther, Bill; Patrick, Heather (1997). Inoculation and pelleting of legume seed. AgFact no. 35. AgResearch
Scott, D.; Maunsell, L.A.; Keoghan, J.M.; Allan, B.E.; Lowther, W.L.; Cossens, G.G. (1995). A guide to pastures and pasture species for the New Zealand high country. Grassland Research & Practice Series No. 4. New Zealand Grassland Association Incorporated, Palmerston North.
Floate, Mike (1992). Guide to tussock grassland farming. AgResearch, Invermay.
This paper has been developed for this site and cleared for reproduction here by AgResearch. Your comments are welcomed and should be forwarded to Bill Lowther bill.lowther@agresearch.co.nz
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