5. THE PASTURE RESOURCE

The description of dominant farm classes within a specified Agro-Ecological environment was presented above in section 4.

Development of the pasture resource

Pre 1850 settlement
The earliest changes in land cover occurred about 800 years ago when fire was used by Maori to hunt flightless birds such as Moa (see section 1) and to clear land for cultivating root crops. Multiple burning events were the likely cause of a change in vegetation from montane forest to montane tussock grassland because forests were unable to regenerate in the period between fire events. With European settlement the vegetation in the last 170 years has had a second period of rapid change with forest clearance and exotic plant introduction. In the mid 1800s extensive grazing of indigenous tussock grasslands began (White, 1999).

Post 1890 settlement by Europeans
Sheep numbers increased rapidly and production (mainly wool) from cleared forest to grazing pastoral systems peaked in the 1870s. Stock numbers then declined as grazing, burning and declining soil fertility reduced production from these unimproved soils. Increased rates of lowland forest clearance for introduced pasture species were triggered by industry expansion when refrigeration opened export markets to meat and dairy products in the late 19th Century. By 1925, it was estimated that >500 exotic plant species (pastoral, arable, horticultural and ornamental) had become established and 3.2 M ha of native, predominantly lowland rainforest, had been converted to pasture. Initially, lowland areas and dissected uplands (Daly, 1990) in the North Island underwent conversion followed by areas in the South Island. As demand for land by settlers grew, increasing areas of broadleaf montane forest were also claimed for pastoral agriculture. About 4.9 M ha of podocarp-broadleaf forest have been converted to grassland since European settlement (Daly, 1990).

From 1920 onwards innovation in science and technology allowed intensification of farming systems. Improvements included mechanisation, amelioration of soil fertility through improved understanding of nutrient requirements for plants and animals, advances in plant and animal breeding and health issues. More recently diversification and improvements in the quality of products produced has dominated. These improvements have been made while maintaining or improving agricultural efficiency to allow production to remain competitive in international markets.

Initially, new pastures were developed from forest by felling of timber which was then left to dry. It was then burnt and pasture seed was broadcast by hand over the ash. Multiple species seed mixes (containing up to 10 different grass and legume species) were recommended for ‘bush burn’ pasture establishment into the 1950s at total seed rates of 20-40 kg/ha. Once established, pasture and regenerating native seedlings were grazed by sheep and cattle and pastures were fully stocked within 12 months of initial tree felling. Later any large tree trunks, which remained after felling, would be hauled out and burnt. This removal of tree stumps may not occur for up to 20 years after the initial tree felling.

Post clearing “Bush sickness” after forest clearing
In the volcanic plateau of the North Island, after initial pasture establishment, livestock showed severe symptoms of ill thrift known as “bush sickness” even when pastures produced adequate feed. In the mid 1930s, cobalt deficiency in livestock grazing pastures sown into soils formed from volcanic parent materials (e.g. pumice) was identified as the cause. Cobalt is required for synthesis of vitamin D in ruminants. This is now rectified by soil fertilizer applications or a mineral drench to livestock.

Development through improved soil fertility
On occasion the initial pasture establishment failed and/or cleared areas of forest began to revert to scrub and forest vegetation. A combination of hard grazing, subdivision, application of lime and superphosphate fertilizers was used to reclaim these areas. This enabled improved pasture plants to be introduced. Where cultivation was possible pasture improvement was more reliable and lime, superphosphate fertilizer and seed were able to be applied. In the 1950s the widespread use of aircraft to apply lime, superphosphate and seed (mainly perennial ryegrass/white clover) to steep hill country was pioneered.

Because of the large proportion of pastures on land with slopes >16° much research was conducted to determine the effects of slope and aspect on pasture production. Important aspects of this work included the effects of stock behaviour in nutrient transfer, seasonality of production (see below) and differences in aerial fertilizer distribution patterns. This information has been used since the 1970s to develop on-farm grazing management systems, aid subdivision decisions and stratify fertilizer applications. Superphosphate applications totalled 794 000 t in 1981 and increased to 1 270 000 t in 2007 while lime applications were 1 355 000 t in 1981, decreased to 561 000 t in 1987 following agricultural reforms, but have increased to 1 487 000 t in 2007.

Hill country development
On some extensively grazed steep hill country (Farm Class 3, Section 4) reversion to manuka and kanuka (Kunzea ericoides) continues to occur. Some farms are encouraging this reversion on marginal land so native species can be re-introduced through planned plantings. Motivation for what is effectively a voluntary retirement of less productive land varies from farm to farm, but is usually a result of cost, ecological sustainability or a combination of the two. For example, the cost involved with retaining marginal areas as productive grassland may not be financially viable, while exotic tree or encouraging native forest reversion in gullies and on steep slopes could be beneficial to stabilise the ground. This means more productive pastures downstream from the steeper slopes are protected from the effects of soil erosion. Further, both plant and animal (native/endemic bird) biodiversity can be increased. Where possible the focus is shifting to tree planting along waterways and fencing off planted areas to prevent grazing livestock from accessing waterways. Deep rooted tree (or pasture) species are encouraged in riparian strips to reduce eutrophication of waterways by capturing nutrients at depth to reduce nitrate leaching and control movement of phosphorus rich topsoil. Farmers also currently anticipate the possibility of gaining carbon credits from converting steep, eroding pasture land back into indigenous or exotic forest.

Nitrogen use for pasture production
Nitrogen fertilizer was rarely used on New Zealand pastures up to the 1980s and nitrogen fixation from white clover was the main source of nitrogen for companion pasture grasses. The use of N fertilizer (mainly as urea - 46% N) has increased dramatically over the last 30 years particularly associated with the intensification in dairy systems. For example, nationally across all agricultural industries, the quantity of urea applied in 1981 was 17 000 t and this had increased to 433 000 in 2007. Nitrogen fertilizer is also used by some sheep and beef farmers to boost grass production in late autumn and early spring. The consequence of N fertilizer use is a reduction in clover content of pastures. Dairy pastures may receive up to 200 kg N/ha/yr applied in split applications of 25-50 kg N/ha. Intensively managed, high fertility pastures are expected to produce about 10 kg DM/kg N applied, while on less intensive pastures responses up to 30 kg DM/kg N applied have been reported. Many regional councils restrict the total amount of nitrogen fertilizer that can be applied.

Irrigation
Access to irrigation depends on factors including topography, cost and ability to obtain a resource consent which dictates the timing and quantity of permitted applications. Across all farm types, which includes horticulture, floriculture, viticulture, agriculture and forestry industries, <3% of New Zealand total land area is irrigated (~620 000 ha). Of this, 16% is in the North Island and 84% in the South Island (Department of Statistics, 2007). Of the irrigated pastoral area, spray irrigation is the dominant method (74%) and flood irrigation accounts for a further 18%.

Dairy farms account for 235 000 ha of the total irrigated land and 111 000 ha of pastoral land used for sheep farming can be irrigated. About 62 000 ha of irrigated land occurs in cropping and mixed cropping systems and a further 51 000 ha on cattle or mixed sheep and cattle farms. 

Pasture growth patterns
In the 1970s and 80s a major government initiative quantified New Zealand pasture production rates in a series of 21 papers on “Seasonal distribution of pasture production in New Zealand” which were published in the New Zealand Journal of Experimental Agriculture (e.g. Radcliffe, 1974). Data were predominantly collected from 30 sites throughout New Zealand for an average of 11 years (range: 8-27 years). The results enabled the pasture production profile to be generated for most regions and are now used as a reference for individual farms. Nationally, mean annual pasture production from perennial ryegrass/white clover based pastures was reported as 10.0-12.0 t DM/ha/yr. Regionally, perennial ryegrass based pasture yields ranged from 5.2 to 17.2 t DM/ha/yr. The variation in seasonal growth rates primarily reflects differences in temperature and rainfall.

Temperature effects on production in summer moist regions
In summer safe environments, where soil moisture deficits are uncommon, the effect of seasonal temperature variation can be quantified. Figure 41 shows that the mean daily pasture growth rates in Dargaville and Winton are lowest in winter and highest in summer and have similar seasonal production patterns. Both sites receive >1 100 mm/yr rainfall. However, the annual yield in Dargaville (northern North Island) was 17.2±3.6 t DM/ha/yr which was 40% more than from Winton in the southern part of the South Island (12.0±2.3 t DM/ha/yr). The main cause of the difference was higher winter production in Dargaville. Spring production was also almost 60% higher than in Winton. Mean air temperatures (1951-1980) for Dargaville were 11.3°C in winter and 13.9°C in spring compared with 6.0°C in winter and 8.1°C in spring for Winton. These differences mean the annual amount of thermal time (°Cd) accumulated, above a base temperature of 5°C, was 3385°Cd for Dargaville compared with 1940°Cd for Winton (McKenzie et al., 1999).

Production in summer dry regions
In regions where soil moisture deficits develop, such as Canterbury, it is unusual for production in winter and early spring months to be constrained by insufficient moisture. However, as soil moisture deficits develop between September and April, mean daily growth rates fall below potential (Figure 42). Annual yields from an irrigated pasture were 10.2±1.0 t DM/ha/yr compared with 5.9±1.1 t DM/ha/yr from adjacent dryland pastures (Rickard and Radcliffe, 1976). The dryland pasture was perennial ryegrass, subterranean clover, with cocksfoot, browntop and white clover. The irrigated pasture was perennial ryegrass/white clover with some cocksfoot, browntop, and Bromus spp. Summer drought can reduce pasture production rates on dryland properties on the east coast to zero which may be less than the temperature constrained winter growth rates. For example, in Canterbury, January (summer) mean monthly dryland pasture production is 13±14 kg DM/ha/d.

Figure 41. Monthly mean daily growth rates (kg DM/ha/d) of perennial ryegrass/white clover based pastures at Dargaville (northern North Island) and Winton (southern South Island) in New Zealand.

Figure 42. Mean daily pasture growth rate (kg DM/ha/d) of irrigated and dryland pastures at Winchmore, Canterbury, New Zealand.

Seasonal variation in mean daily growth rates
Figure 43 shows the upper and lower pasture production variability of mean monthly growth rates (kg DM/ha/d) at a North Island hill country site (Wairakei, Farm Class 4; Section 4) and flat dryland South Island site in Central Otago (Otago Plateau, Alexandra; Farm Class 1, Section 4). Grey lines show one standard deviation in monthly growth rates measured at each site. The greatest absolute variation occurs in summer and reflects the effect of differences in summer rainfall and consequently soil moisture availability. The least variation occurs in winter months when growth rates are solely limited by temperature. It should be noted that dry matter production from unimproved hill country pasture may be only half that of an improved hill country pasture. Much of this is due to lower DM production in winter months from swards which become dominated by browntop and flat weeds. Low legume content compounds the degradation of improved pastures over time and N fixation and transfer to companion grasses is decreased. Improved grasses which require higher fertility conditions, such as ryegrass, fail to persist in competition with species suited to lower fertility conditions such as browntop.

Figure 43. Mean daily growth rates (kg DM/ha/d) of pastures on a hill site at Wairakei (▼; top) in the North Island and on the Otago Plateau (●; bottom) at Alexandra in the South Island. Grey lines are ± one standard deviation and production falls within that range in two out of three years.

Effects of topography

 Altitude
Temperature decreases as altitude increases (about 2°C/300 m) while rainfall may increase (McKenzie et al., 1999). For improved hill country in Central Otago, this resulted in a 450 kg DM/ha/yr yield reduction per 100 m increase in altitude. Because of low temperatures constraining production in winter months, the majority of production in dryland systems is limited to spring months before water stress develops and limits production in summer. At Poolburn (430 m) annual pasture production was 2.8 t DM/ha from a mean annual rainfall of 400 mm. The growing season (Sept-May) accumulates 1500°Cd above a base temperature of 5°C. At an adjacent irrigated site annual production was 8.7 t DM/ha. During the cold five- month winters growth is negligible. Conserved feed from any irrigated pastures is therefore essential for farmers in the Poolburn district (South Island High country; Farm Class 1, Section 4).

Aspect and slope
Differences in total annual production between sunny and shady slopes varies from site to site depending on whether temperature or soil moisture is the major constraint to production (McKenzie et al., 1999). At a high rainfall North Island site, Gillingham (1973) reported yields on N facing slopes were 10% higher than from S facing slopes. He also showed that slope accounted for 22% of the observed variation in pasture growth rates. Annually yield decreased by 109±26 kg DM/ha/yr for every degree increase in slope. The remaining variability was attributed to differences in microclimate, soil fertility and pasture utilisation. In Canterbury hill country where summer soil moisture deficits are common, Radcliffe et al. (1977) reported annual DM yields of browntop dominant pasture from a shady (SW) slope (20-30° at 290-440 m) over a three year period of 7.4 t DM/ha/yr. This compared with 6.1 t DM/ha/yr produced on sunny (N-NW) slopes at the same location.

Animal behaviour
Animal behaviour is also modified by slope and aspect with consequent effects on nutrient transfer particularly within large (>20 ha) un-subdivided hill and high country blocks. These are usually set stocked for long periods each year. Livestock camp in areas that offer the most protection from environmental conditions (Lambert and Roberts, 1978). Gillingham (1980a, 1980b) reported livestock camped on land with slopes of 0-10°. In these camps pasture production was dominated by perennial ryegrass. Yields decreased from 11.0 t DM/ha in stock camps to 5.0 t/ha on slopes of 45°. This was equivalent to a reduction of ~850 kg DM/ha per 5° increase in slope. Faecal P transfer from slopes to stock camps meant soil P levels that were 2-3 times greater than the annual pasture requirement. Saggar et al. (1990) reported 60% of faecal P returns were made to the land with slopes <12° which accounted for 30% of the land area in their study.

Botanical composition of pastures on and near stock camps is strongly influenced by increased N and P fertility and the degree of soil moisture deficit at different sites. At Ballantrae in the Manawatu, annual DM yield production of unimproved pasture was 2.8 on the north aspect, 3.0 on the west, 9.7 on the east and 3.6 t DM/ha on south facing aspects (Lambert and Roberts, 1978). Botanical composition was dominated by native Notodanthonia grass species on the north aspect; perennial ryegrass and mouse-eared chickweed (Cerastium glomeratum) on the south; Yorkshire fog on the east and south and Nertera setulosa in the west and south aspects. Browntop and sweet vernal had similar cover at all sites probably due to their wider tolerance of soil fertility and environmental conditions.

Grass endophytes

The presence of endophyte is vital to maintaining long-term productivity and persistence of ryegrass based pasture due to the protection it offers against pests. The presence of wild type endophyte has been shown to deter black beetle (Heteronychus arator), cutworm (Graphania mutans), root aphid (Aploneura lentisci), porina (Wiseana cervinata) and pasture mealy bug (Balanacoccus poae) (Easton, 1999). Another major pest affected by endophyte is Argentine stem weevil which has been estimated to cost the pastoral industry NZ$ 46-200 M annually through pasture damage (Prestidge et al., 1991).

To maintain protection from insects and minimise livestock health issues novel strains of endophytes, such as AR1 and NEA2, have been developed. These endophytes are non-existent in the neurotoxic lolitrem and ergovaline but contain high levels of peramine, an alkaloid to which Argentine stem weevil is very sensitive. 

However, peramine is not a broad spectrum pesticide and consequently further development of novel strains continues. The recently released AR37 endophyte does not produce peramine, lolitrem or ergovaline alkaloids. It does produce epoxy-janthitrem compounds which confer pest deterrence to a wider range of invertebrate pests than the AR1 endophyte. Some staggers may still occur in livestock grazing AR37 infected ryegrass. Farmers in the warmer areas of New Zealand, where there is the greatest pest challenge to ryegrass productivity and persistence are encouraged to sow AR37 ryegrasses. AR1 is recommended where there is sporadic insect pest attack in more temperate areas and nil-endophyte seed may be safely sown in cool southern or high altitude regions.

Tall fescue endophytes
Similar novel endophyte technology has been applied to tall fescue in recent years and has led to the release of the MaxP endophyte (Neotyphodium coenophialum). Severe heat stress and necrosis can occur in livestock grazing wild type endophyte infected pastures in other countries (e.g. U.S.A.). However, in New Zealand wild type endophyte infected tall fescue is only found on roadsides. Tall fescue in grazed pastures has always been endophyte free. Thus, the development of this novel endophyte was primarily focused on use in international markets. It is likely to increase persistence in New Zealand environments compared with the current endophyte free lines. Development of loline producing endophytes (Ball and Tapper, 1999) particularly for tall fescue and meadow fescue is a current research area (Patchett et al., 2008). These loline producing endophytes show evidence of wound induced alkaloid redistribution by increasing concentrations in areas of tissue under insect attack.

Research is continuing to develop novel endophytes. The aim is to ensure pasture yield and persistence from ryegrass and tall fescue based pastures is maintained at levels comparable to wild type endophyte infected pastures but avoidance of adverse effects on livestock.

Pasture Species

Major species
New Zealand farmers have a large range of improved grass, legume and forage crop cultivars to select from. For perennial ryegrass there are different endophyte options (nil, wild type or modified ‘novel’; see above) available in over 60 different perennial/long rotation cultivars. These cultivars also differ in flowering time, cool season activity and ploidy level. In addition there are 20+ Italian, annual and short rotation ryegrasses. There are at least 15 cultivars of tall fescue, cocksfoot, bromes (Bromus spp.) and timothy. The most commonly sown pasture legume is white clover with 20+ cultivars that vary in leaf size and stolon density. There are several cultivars of red and subterranean clovers and 10+ lucerne cultivars commercially available or registered for use. Subterranean clover seed is imported from Australia and cultivars vary in flowering date (early, mid or late) and hardseededness rating. There are also pasture herbs, namely chicory and plantain (Plantago lanceolata) available (Caradus, 2008).

The development of new pasture and forage cultivars is ongoing and commercial companies often work in association with Government owned Crown Research Institutes during breeding, selection and development. Locally bred, pest and disease resistant cultivars which are suitable for grazing or conservation are most widely sown but some cultivars bred in Europe, North America, Argentina or Australia are also sown. These cultivars may have cool season activity or may tolerate more frequent grazing.

Minor species

Cultivars of browntop, Yorkshire fog, Caucasian clover (T. ambiguum), Lotus pedunculatus, L. corniculatus, alsike clover (T. hybridum) and sulla (Hedysarum coronarium) have been developed for use in New Zealand but are rarely sown. Recently, interest in Lotus spp. and sulla has been revived because of their tannin content which may reduce bloat incidence, gut parasites and methane gas production by ruminants while increasing protein absorption. Adoption of annual legumes other than subterranean clover, to produce high quality spring feed and nitrogen fixation in dryland regions has increased. Seed is mainly imported from Australia. Persian (T. resupinatum) and balansa (T. michelianum) clovers are tolerant of wet soils in winter. Arrowleaf (T. vesiculosum) clover is very late flowering and may complement white and subterranean clovers in permanent pastures.

Use of alternative pasture species, which have definite advantages in specific environments, is often restricted due to difficulty in establishment, perceived high cost of new species and widespread promotion of ryegrass/white clover pasture technologies. For example, Caucasian and strawberry (T. fragiferum) clovers are perennial legumes suitable for some New Zealand pastures. However, their use is limited by high seed costs and availability of seed. Slow establishment further limits uptake of these two species because of excessive sowing rates (20-25 kg/ha) of vigorous perennial ryegrass. The clovers are suppressed and fail to establish. Consequently, farmers consider slow establishing species to be failures.

Species selection

Selection of the appropriate pasture species depends on the environment where it is to be sown. Table 12 shows that ryegrasses are highly suitable for inclusion in moist lowland environments (Farm Class 5, Section 4) but are less suitable for South Island High Country properties (Farm Class 1, Section 4). In moist hill country (Farm Class 4, Section 4) recommended grasses include ryegrass, cocksfoot and grazing bromes (Bromus stamineus and B. valdivianus) while lotus, white and red clovers are the most suitable legumes. Species suitable for use in farming systems which experience periodic water stress (“dryland”) include; cocksfoot, bromes, tall fescue, lucerne and subterranean clover.

Pastures for warm, summer moist regions
In warm, summer moist environments in New Zealand, perennial ryegrass/white clover is the preferred pasture combination. These pastures can be easily established and are tolerant of a wide range of management practices. They can be set stocked in spring during lambing and calving and then rotationally grazed throughout the remainder of the year. Typically, these pastures are spring or autumn sown into a firm and fine seedbed with 10-20 kg/ha of perennial ryegrass and 1-3 kg/ha of white clover seed. Timothy, chicory, plantain and/or red clover may be added to this basic mix. A clean, weed free seedbed is particularly important when herb species are included in pasture mixes as the use of herbicides for control of broadleaf weed species is restricted if chicory or plantain are included. 

Subtropical C₄ grasses such as paspalum (Paspalum dilatatum) and Kikuyu (Pennisetum clandestinum) may dominate pastures in moist northern areas of the North Island when perennial ryegrass has lost vigour after stress periods (insect damage, summer drought, winter pugging). These aggressive C₄ grasses are vigorous in the warm summer and autumn but have lower production in winter and spring when temperatures are outside their optimum ranges. Their quality is inferior to perennial ryegrass. Frequent pasture renovation is often required to control Kikuyu particularly in the Northland region. Glyphosate is used to control C₄ grasses prior to overdrilling perennial ryegrass. Insect damage in the warmer North Island regions is more severe than farther south and suitable novel endophytes (see above) in ryegrass and tall fescue cultivars are therefore recommended.

Cool, summer moist regions
The Southland district, in the south of the South Island, has the best examples of perennial ryegrass/white clover pastures in cool summer moist environments (see the Winton production curve in Figure 41). Pasture insect pests develop more slowly in this cooler environment and their populations seldom reach pest proportions (e.g. Argentine stem weevil completes only one generation/year). Nil endophyte ryegrass can thus be sown with relative safety. Timothy is well adapted to the climate and is more sociable with clovers than the more competitive ryegrass. White and red clovers are productive during summer months. In poorly drained and lower fertility areas Yorkshire fog and browntop become dominant in older pastures. Brassicas (swedes and kale) and annual ryegrass forage crops are grown for winter feed, as part of pasture renewal programs (see below), to complement silage made in summer from cereals and pasture.

Dryland pasture options
In summer dry areas, pastures may be sown after a summer fallow (see below) which provides opportunity for thorough weed control and accumulation of soil moisture.

These environments develop summer soil moisture deficits because of combinations of low annual or seasonal rainfall (<700 mm/yr), high warm season evapotranspiration, and shallow, stony soils with low waterholding capacity. Cocksfoot is the second most commonly sown grass in New Zealand and is used for these regions. It is less affected by drought than perennial ryegrass and persists and recovers leaf area and growth more rapidly than perennial ryegrass.

White clover performs poorly in these dry environments especially after the loss of its taproot 12-18 months after sowing. Subterranean clover cultivars imported from Australia are recommended as the main companion legume in cocksfoot based pastures. The annual life cycle of subterranean clover means that it produces high quality spring feed before and during flowering and it then buries its seed burrs in November/December to complete its life cycle. This nullifies competition for scarce water between the grass and legume in summer months. At “Tempello”, a dryland hill country farm in Marlborough, pre-weaning lamb growth rates on a dryland subterranean clover dominant hill country property have increased with improved subterranean clover management from 227 g/hd/d in 2001 to 328-402 g/hd/d (Grigg et al., 2008). Meat produced from the 2 800 ha of effective land (4 800 ha total area) has increased from 60 to 76 t liveweight/year despite a 12% drop in total ewe numbers. Lamb weaning weights have increased from 27 kg LW/hd (2001) to 32.5 kg LW/hd in 2006.

In years with moist summers, volunteer white clover may be a valuable component of dryland pastures. Other annual clovers are currently being tested on dryland farms and several adventive clovers, medics and lotus species are common in lower fertility dryland pastures.

Lucerne
Lucerne is used on the dry east coast of New Zealand for direct grazing and conserving as hay or silage. The area of lucerne sown decreased from 220 000 ha in 1975 to 180 000 by 1979 (Department of Statistics, 1979; Purves and Wynn-Williams, 1989). The rapid change in area was primarily a result of the accidental introduction of the blue green aphid. The cultivars available at the time were decimated as they were not tolerant/resistant to attack. The total area in lucerne in 1992 was only 72 000 ha as stand production and persistence were compromised by pests, diseases and poor management (Purves and Wynn-Williams, 1994). The need for rotational grazing combined with the perception that it is more expensive to grow compared with ryegrass/white clover resulted in a reluctance to grow lucerne. The cultivars currently sown differ in levels of winter activity and pest and disease resistance.

The area in lucerne is rapidly expanding with recent demonstrations of high productivity and profitability. For example, in Marlborough at “Bonaveree” farm with a mean annual rainfall of 530 mm, the area in lucerne has more than doubled from 120 to 300 ha between 2003 and 2009. This lucerne was direct grazed with only true surplus herbage conserved. The economic farm surplus has increased from NZ$ 30/ha to almost NZ$ 140/ha even though annual rainfall decreased over the same period. In 2006/07, lambs averaged 396 g/hd/d from birth to weaning and over 80% of lambs were finished and sent for slaughter by mid December at 13-14 weeks of age (Avery et al., 2008).

Increasingly, where water is scarce for growth, this deep rooting, high quality species is sown on the deepest soils to extract moisture from depths that are inaccessible for grasses. Yields vary throughout the country which reflects differences in environment, soils and management. Annually yields can range from <3.0 to >28.0 t DM/ha.

The quality, particularly crude protein and metabolisable energy, of lucerne herbage is strongly affected by regrowth duration because of changes in the leaf:stem ratio (Brown and Moot, 2004). Recent changes in lucerne grazing management have been critical for maintaining stand production and persistence (Moot et al., 2003). Failure to allow adequate partitioning of carbohydrates to roots by allowing adequate regrowth duration (>5 weeks) between grazing events and preventing flowering in late summer or autumn reduces potential production in the following year (Teixeira et al., 2008). In New Zealand lucerne is rarely sown in mixtures because of its need to be rotationally grazed throughout the year. However, some farmers may sow lucerne in mixes with prairie grass to produce cool season feed while in cool dry areas cocksfoot is useful to combat wind erosion.

Alternative pasture grasses
Tall fescue (nil endophyte or novel non toxic types), prairie grass (Bromus willdenowii), grazing bromes, timothy and phalaris (Phalaris aquatica) are all available for use in permanent pastures in New Zealand. In higher fertility lowland sites, tall fescue with novel endophyte is likely to be more persistent than ryegrass and could have increased summer grass production as the optimum temperature for photosynthesis of tall fescue is higher than that of ryegrass. Tall fescue is also likely to be more legume friendly to clovers in mixed species pastures than ryegrass because of its greater thermal time requirement for field emergence and less vigorous seedling growth compared with perennial ryegrass (Moot et al., 2000).

Bromus species provide greater cool season production than perennial ryegrass but tend to be vulnerable to insect pests and perform poorly on acid soils or poorly drained sites. Timothy has very small seed (~0.4 g/1 000 seeds) compared with perennial ryegrass (2.0 g/1 000 seeds), thus establishment can be compromised when sown too deep. Furthermore, field emergence is slow for timothy (230°Cd) compared with 160°Cd for ryegrass so timothy seedlings are out-competed at establishment (Moot et al., 2000). Timothy is a late flowering grass which retains nutritive quality later into the season, and is less competitive with companion legumes, than ryegrass. It is frequently used in hay crops. Phalaris is valued as a minor component of multiple species pasture mixes as it tolerates root attack by grass grub (Costelytra zealandica) but is rarely used as the primary grass species because it may cause irreversible staggers in livestock.

Low fertility pastures are frequently browntop dominant. This mat forming perennial tends to exclude more desirable species through its ability to compete for water and nutrients, predominantly scarce phosphorus. In moist hill country it may be suppressed by mob stocking at high rates in winter. Heavy trampling then tends to favour ryegrass/white clover. Other introduced grasses which may invade improved pastures over time include: sweet vernal, crested dogstail and Yorkshire fog.

Weeds
About 50% of total plant species are exotic and some have become invasive weeds. As gaps open in pastures after drought, flooding, pest damage or overgrazing, annual and perennial weed species may invade. Purchase of certified seed has restricted the level of contamination in recent times. In many cases initial weed introductions occurred from seed sown when pastures were first broken out of scrub and forest over 100 years ago from contaminated seed imported into the country. In pastures which are not normally exposed to water stress, giant buttercup (Ranunculus acris), docks, ragwort (Senecio jacobaea) and dandelion (Taraxacum officinale) are the main weed species. In swampy areas species such as rushes and sedges may be present whereas in high country bracken fern, hawkweeds (Hieracium) and browntop may invade improved pastures if soil fertility levels are not maintained. Perennial rhizomatous species such as browntop, twitch, Californian thistle and yarrow (Achillea millefolium) are common weeds which invade dryland pastures.

Annual weed grasses are Poa annua, barley grass and Vulpia spp. In addition, C₄ annuals such as barnyard grass (Echinochloa crus-galli) and summer grass (Digitaria sanguinalis) are common in warmer, summer dry regions (northern North Island). Annual ripgut brome (Bromus diandrus) and the perennial Chilean needle grass (Nassella neesiana) are major grass weeds in hill country which are capable of creating serious livestock health issues and contamination of wool, skins and carcasses which may be rejected during processing.

Pasture renewal (see below) is required as pasture productivity and quality declines. Species such as Poa annua, shepherd’s purse (Capsella bursa-pastoris), chickweed (Stellaria media), fathen (Chenopodium album), nightshade (Solanum nigrum and S. physalifolium) speedwell (Veronica persica), twin cress (Coronopus didymus), cleavers (Galium aparine), mallow (Malva spp.), horehound (Marrubium vulgare), hawksbeard (Crepis capillaris), hawkbit (Leontodon taraxacoides), catsear (Hypochaeris radicata), dandelion, thistles (scotch, nodding, Californian), Hieracium spp., gorse and broom (Cytisus scoparius) are all common pasture weeds. The woody weed species such as gorse, broom and sweet brier are particularly expensive to control while horehound may present significant problems in lucerne stands. In dairy pastures giant buttercup and ragwort are major weeds in some districts.

Weed control
Weed control in New Zealand pastoral agriculture uses an integrated approach. Combinations of cultural, chemical, mechanical and biological practices are implemented to reduce the impact of least desirable weed species on pasture and animal production. Ensuring pasture cover is maintained by a healthy and vigorous sward minimises invasion by less desirable species. Chemical spraying of fence lines and road verges reduces invasion into surrounding paddocks. Topping, burning and chemical herbicides are targeted methods to prevent seed set of weed species. The decision to employ chemical control or to enter into pasture renewal depends on the species, plant population and the potential for the infestation to reduce farm income.

In most cases, crop rotations, fallow periods, cultivation and grazing management are the most common methods of weed control. Use of pest and disease resistant cultivars and timing farming operations to minimise potential for pest attack or disease are also common practice. Use of chemical control for weeds, pests and diseases is common in susceptible arable and horticultural crops and, when necessary, in establishing pastures and forage crops.

In established pasture chemical control methods are only triggered when failure to control the degradation caused to the pasture will result in an economic loss. For example, annual dicotyledonous weeds may be tolerated in established pastures but ingress of perennial rhizomatous weeds such as Californian thistle triggers a combination of control methods. In spring and summer, thistles are permitted to form seedheads but these are topped before the seed matures. This depletes reserves in rhizomes. In autumn, as the plant begins allocating carbohydrate below ground, a systemic herbicide is applied which is also translocated throughout the root system. Herbicide selection depends on whether the thistle has invaded a monoculture or mixed species pasture. A broad spectrum broadleaf herbicide is applied to grass or cereal monocultures. In a mixed species pasture containing grass and legumes the broadleaf herbicide should be selective so legumes are not killed.

Pest control
Pasture and crop pest control must be cost effective and timed to ensure maximum control is achieved. Where possible, if a pest is a known problem in a region, farmers select species or cultivars which are tolerant or resistant to attack. An integrated approach to pest management is recommended because total reliance on chemicals can result in development of resistant pest populations. Other management strategies include: crop rotations, cultivation, ensuring time of sowing does not coincide with peak pest incidence, removal of crop residues, mob stocking and irrigation. Pest thresholds are developed as the levels beyond which yield and/or economic losses are likely. For example, in susceptible established pastures action is recommended at infestation rates of 100 grass grubs/m² or 20-40 porina caterpillars/m². These two major native pests of pasture have thrived with the development of productive grazed pastures.

Several successes have been achieved with biological control of pest insects. Notable examples include the introduction of the parasitoid wasp (Microctonus hyperodae) to control Argentine stem weevil and Microctonus aethiopoides as a parasitoid for Sitona discoideus a weevil which caused serious damage to lucerne.

Disease
Plant disease control is not usual practice in grass based pastures but may be required in herbage seed crops and supplementary forage crops. One of the major objectives of plant breeders is to select for disease tolerance in pasture species. Cultivars which are susceptible to diseases tend to be less productive and are usually rapidly replaced with newer genetic material. Methods of disease control in crops and pastures fall into four main categories. These are to reduce or eradicate the source of disease, use resistant cultivars, protect the host plant and/or alter the environment (soil, crop and storage). Spread of disease may require an insect vector; thus by controlling the insect (e.g. aphids) the potential for infection can be reduced.

Pasture renewal programs
Crop rotations within New Zealand pastoral agriculture are essential to ensure long-term technical and financial sustainability of the pasture resource (Moot et al., 2007). There are multiple objectives of the cropping phase between periods of pasture. These include to:

1. Maximise short and long term income,
2. Provide feed of adequate quantity and quality to meet seasonal requirements of grazing livestock,
3. Manipulate soil fertility levels by complementary use of depletive and/or restorative crops,
4. Ensure mobile nutrients are prevented from winter leaching as they are retained in plant tissue of the ‘green manure’,
5. Break life cycles of pests and diseases and allow appropriate weed control,
6. Spread seasonal demand for on-farm labour and machinery and,
7. Minimise idle land.

In any pasture renewal program it is undesirable to replace the existing run-out pasture directly with new pasture, because such a sequence fails to address why the vigour of the existing pasture declined. It is recommended that 10% of a farm undergoes renewal every year although this may vary from 5-20% depending on the farming system.

Maize in pasture rotations
Maize is one of the crops which can be used in pasture renewal as it tolerates a wide range of herbicides to control problem weeds and may also provide useful income through the sale of grain or forage for silage production. There are at least 40 different hybrids of maize available which differ in maturity rating and disease resistance. Typically, maize silage yields, when grown with adequate moisture and nutrients, range from 16.0-25.0 t DM/ha depending on the environment. 

As a C₄ species, maize is commonly grown in the warmer North Island areas of New Zealand where sowing can commence in mid October. Over 90% of the area sown in maize, for silage or for grain, is in the North Island. Canterbury is the southern limit for maize production due to potential for frosts at both ends of the growing season in more southern regions. In cooler areas sowing does not occur until mid November and hybrids with lower comparative maturity ratings, which require accumulation of less thermal time to reach maturity, must be used or there is a risk of crop failure.

With both conventional cultivation and direct drilling the first herbicide is applied about one month prior to sowing maize and the pasture is grazed about 10 days later. The paddock is then cultivated and maize is sown. If necessary, the area is given a second herbicide application prior to direct drilling. Where problem grass species such as browntop, Kikuyu and summer grass are present these may be sprayed out the previous autumn and the paddock sown in Italian type ryegrass for feeding in situ over winter and early spring.

For successful pasture establishment it is desirable to harvest the maize for silage in mid March (autumn) rather than for grain that may not mature until May or June. Following harvest the paddocks are then sown back into pasture using either conventional cultivation or direct drilling. In some cases two or more maize crops may be grown prior to establishing a new perennial pasture. Cereal crops for grazing in situ may be sown in the period between the maize crops.

Brassicas in pasture rotations
There are also 40+ forage brassica cultivars commercially available and over 300 000 ha of brassicas are sown annually in New Zealand farm systems. Of these around 20% will be considered failures (de Ruiter et al., 2009) due to poor preparation/sowing or inadequate control of pests and diseases during establishment. Leaf or bulb turnips (Brassica rapa syn. B. campestris) and rape (B. napus spp. biennis) are the main brassicas used to provide supplementary forage in the summer/autumn months while winter feed deficits are filled by swedes (B. napus spp. napobrassica) or kale.

If a brassica crop fails to establish then a winter greenfeed cereal, such as oats or barley, can be oversown into the paddock in April to minimise yield losses. Cereals are established at a rate of 80-120 kg/ha and can produce 2-4 t DM/ha of winter feed depending on soil fertility and time of sowing. Break-grazing using back fencing is essential if regrowth is required.

In most North Island Hill country properties (Farm Classes 3 and 4; Section 4) about 5-10% of the farm area can be cultivated. This area can be used to incorporate forages into the farming system. The rotations employed depend on financial considerations and the identification of expected periods of feed deficit. Where high quality summer feed is required for lamb and beef finishing (Farm Classes 5, 6 and 8, Section 4) a leaf turnip such as ‘Pasja’ is used. Kale, sown in late spring, allows transfer of feed from summer to winter months. The area available for summer grazing is reduced by establishing kale in spring but the bulk of dry matter produced by the crop is available as standing feed to meet stock demand in winter months.

When kale is used rotations are usually:

old grass pasture → kale (1-2 crops) →spring sown new pasture.

In environments with over 800 mm rainfall/yr kale can be sown in November (late spring) and can, with appropriate management, accumulate >20.0 t DM/ha by the following winter. However, yields can be highly variable (Table 13) depending on nutrient availability, environmental conditions and establishment and management practices. For example, in Canterbury, kale yields were 23.0 t DM/ha from an October sowing (8 months after sowing) and 17.0 t DM/ha for the December sowing (6 months) (Brown et al., 2007) and grew at a rate of 8 kg DM/ha/°Cd above a base temperature of 0°C. Kale is grazed ‘in situ’ and break fenced so stock are allocated a daily feed allowance. If two successive kale crops are grown in the rotation, yields from the second crop are generally lower than the first.

Pasture renewal programs in different farm systems
To maintain animal production, pasture renewal programmes have been developed for most land classes. Where possible, these usually involve a cropping phase but on land that cannot be cultivated oversowing or direct drilling of species is common. In drier South Island environments, the pasture renewal rotations differ with the provision of a summer feed supply during the rotation. Typically rotations are:

old grass pasture → Italian ryegrass for winter greenfeed → leaf turnip or rape for summer feed→autumn sown pasture.

This would ensure successful pasture establishment after autumn break rains, because spring establishment is unreliable.

South Island Finishing/Breeding properties (Farm Class 6; Section 4) employ rotations to ensure adequate feed is produced to meet livestock demand. This is because these systems experience cold winters and summer drought which limits pasture feed production (Moot et al., 2007). Crop rotations provide maintenance feed in winter months and green feeds are used to meet late winter/early spring feed demand which increases during lambing/calving and lactation. Annual greenfeed crops have the added benefit of depleting soil nitrogen following lucerne stands. Old lucerne stands, which are identified for renewal when plant population declines and perennial weed species begin invasion, are cultivated in early spring and left fallow until autumn when a greenfeed Italian ryegrass or cereal is sown. This is fed to stock in late winter/early spring and then cultivated by late October. The paddock is fallowed to accumulate soil moisture, and allow appropriate chemical weed control, until late January when turnips are sown to grow aided by the conserved soil moisture. Turnips are grazed in winter (July) allowing seedbed preparation in early spring before sowing another lucerne stand. If the paddock is being sown to pasture a second summer fallow is used to conserve moisture before the pasture is autumn sown.

Intensive South Island finishing systems (Farm Class 7; Section 4) are generally in summer safe environments. Their main period of feed deficit occurs in winter when temperature limits production from conventional temperate pasture species. There are two main pasture renewal practices (Moot et al., 2007). In the first, the old grass pasture is sown into swedes which are winter (June/July) grazed and then new pasture is sown in spring. Alternatively, a cereal crop is sown in October after the swedes and prior to establishment of the new pasture. These cereal crops are either used as whole crop silage or harvested for grain prior to autumn establishment of the new pasture.

New Zealand’s pastoral resource and integrated agricultural systems rely almost entirely on improved pastures developed by human activity. Prior to settlement the country was forested (see section 1 and Figure 2) and even the high country tussock grasslands, with their low stock carrying capacity (Farm Class 1, Section 4), would not exist without the repeated burning events that occurred for hunting. Thus, most of the opportunities for the future focus entirely on improved pasture species and their management.

Because the New Zealand economy is dominated by the success or failure of its pastoral industries it is important to initially discuss physiological limitations to pasture yield within its pastoral systems. Increases in pastoral production will come from intensification of land which is currently in pasture. The land area devoted to pastoral production has declined over the last decade and, given the country’s topographic constraints, it is unlikely that any new areas will be converted to pastoral agriculture. Intensification is on-going with increasing areas under irrigation, the conversion of sheep and beef farms to dairy production and the more intensive use of easier hill country.

Improved on-farm management
New Zealand farmers readily adopt new technology when they perceive a commercial advantage, but there will always be room for improvement in the standard of farm management. Dairy farmers are characterised as rapid adopters of new technologies in contrast to more conservative sheep and beef farmers. There is widespread acceptance of ryegrass as the principal component of dairy pastures with white clover as the only suitable legume. This widespread belief is strongly reinforced by farm advisers and seed company publicity that is difficult to challenge if circumstances require widespread adoption of pasture alternatives. For example, the adoption of tall fescue, lucerne or lucerne/grass mixed pastures for grazing in the dairy industry may be difficult to promote without significant demonstrable advantages.

In the sheep and beef sector there are moves towards more stratification within the industry. This would ensure that the pasture resource is used more efficiently with store lambs and young cattle from hill country farms (Farm Classes 1-4; Section 4) being supplied to lowland intensive finishing farms (Farm Classes 5-8; Section 4) on contract. This closer integration between farm classes results in more secure returns for the breeding farms and a guaranteed supply of quality livestock for the finishing enterprises. This would also by-pass the fickle nature of store stock auctions. These developments are being accelerated by the increasing influence of large company owned farms which have a range of properties in both wet and dry regions. They are then ideally situated to use their complementary pasture resources by trucking livestock to graze high quality pasture at their various properties. It often makes greater business sense to move animals than buy conserved forages or to grow large areas of winter feed in a self contained family farm.

Management improvements on-farm over the next decade are likely to focus on increasing production efficiencies (e.g. per ha, per mm of water, per unit of P, S or N applied, per labour unit, etc). This will occur in parallel with attempts to decrease environmental impacts of intensive pastoralism. Amongst others, mitigation or reductions are required to 1) reduce methane and nitrous oxide gas outputs from ruminants and grazed pastures and 2) reduce nitrate leaching from winter forages grazed in situ and from urine patches. These two areas are current subjects of intensive research where some progress is being achieved.

Management technologies which will achieve greater resource use efficiencies and which are currently being demonstrated and promoted to farmers include:

• Use of improved cultivars and pasture species,
• Faster and more precise methods for measurement of pasture mass to allow more efficient grazing management,
• Centre pivot irrigation,
• Soil moisture monitoring to ensure irrigation water is applied only when required,
• Routine use of soil and herbage testing to determine fertilizer requirements,
• More precise fertilizer and herbicide application using GPS,
• Once a day milking of dairy cows and
• Computer packages to assist in long and short term decision making (record keeping, accounting, marketing, pasture growth models, fertilizer and irrigation calculators).

The need to at least maintain production per unit area, given that there is no more land available for pastoralism, while facing the requirement that farmers must reduce the environmental impacts of intensive ruminant grazing, is the greatest challenge facing New Zealand agriculture.

The trend towards fewer larger farms, both corporate and family owned, will generate some economies of scale with bulk purchasing of inputs such as fertilizer and more importantly larger flocks and herds that will allow selection from a wider gene pool to breed animals which can more efficiently convert forage into milk and meat. However, the trend to larger paddocks on large farms may lead to less precise use of land where soils and topography may vary considerably over small areas.

Opportunities to overcome topographical limitations (also see section 5)

Over 60% of New Zealand’s pastoral land is on slopes steeper than 15° and pasture production is unlikely to reach the theoretical yield limits. Some of the physical limitations for hill country pastoralists include:

• Steeper country cannot be safely worked with tractor drawn implements;
• Aerial applications of herbicide, seed and fertilizer are required but are expensive;
• Access is more difficult and soil erosion is more likely.

Interactions between topography, plant biology and climate, in most cases, cannot be altered. Hill country farmers must understand the negative effects these interactions can have on productivity and seek to minimise their potential effects. For example, nutrients will continue to be transferred from steeper slopes to high points and less steep areas of un-subdivided paddocks. More intensive subdivision of hill pastures and strategic placement of water and salt supplies (Gillespie et al., 2006) may moderate animal movement and grazing intensity of steep slopes. However, it seems that there is little that can be done to change the camping behaviour of free grazing livestock. Fencing dry warmer north and west slopes from cooler, later maturing east and south slopes is on-going current practice, as is the separation of higher producing rolling country from steeper mid altitude from cooler higher country, undeveloped shrub vegetation from productive pasture. As environmental imperatives become more urgent rivers, streams and steep eroding gullies will be fenced to exclude livestock.

Advances are being made using GPS technologies to more precisely spread fertilizer from fixed wing aircraft but helicopters, which are more expensive, would be required to achieve ideal placement over much of the finely dissected hill country of New Zealand.

Opportunities under dryland conditions
The majority of pastoral systems in New Zealand are managed under dryland conditions and thus are completely reliant on rainfall to provide adequate water for growth. In some regions water stress is uncommon as the quantity and distribution of rainfall is adequate to maintain growth. In these areas, or in irrigated systems, where N is non-limiting water use efficiencies of >30 kg DM/ha/mm water transpired are possible (Moot et al., 2008). However, the water use efficiency (WUE) of an average temperate pasture (e.g. perennial ryegrass with 10% white clover), which is normally N deficient and exposed to water stress during the peak growth period, may only produce ~10 kg DM/ha/mm. Clearly the scarce water resource is used inefficiently when grasses are N deficient. Annual yields from dryland pastures supplied with non limiting N can double yields and may be 50% greater than N deficient irrigated pastures (Peri et al., 2002b; Mills et al., 2006). Therefore, there is a strong case for developing pastoral farming systems where much greater emphasis is placed on legume production. Legumes grown alone or mixed with less aggressive grasses and/or herbs will not require N fertilizer and the dry matter grown will be more nutritious.

Nitrogen and legume use
Animal nutritionists tend to be critical of pure legume herbage diets because of the high crude protein content of temperate legume foliage (25-30%). They emphasise that ruminants require only 15-18% crude protein and that greater amounts supplied in pasture diets are a physiological burden which results in extravagant losses of N in urine. However, despite this, grazing animals prefer to select a diet which is 70% legume and 30% grass. Also, liveweight gains and milk production/animal are maximised at similar high proportions of legume in ruminant diets.

The maximum yield which can be achieved from perennial temperate pasture species is about 28 t DM/ha/yr when N and water are non-limiting (Peri et al., 2002a) but high rates of N (>600 kg N/ha/yr) are required for C₃ grasses to reach this maximum yield (Mills et al., 2006) and these are unlikely to be economically viable or environmentally sustainable for ruminant production systems. This rate also exceeds the arbitrary 200 kg N/ha/yr maximum N fertilizer rate set by environmental agencies. In contrast, nodulated legumes with N self sufficiency and efficient light capturing leaf canopies, such as lucerne, also have a potential yield of 28 t DM/ha/yr (Brown et al., 2005). Clovers with less efficient leaf canopies may have a yield limit of about 18 t DM/ha/yr as monocultures. This is at least 1.5 times the yield expected from typical perennial grass clover pastures where the clover content is normally only about 10% of total annual production. Such pastures are invariably N deficient because of low N inputs from the clover which struggles to compete with grasses.

While grass dominant pastures, which do not receive N fertilizer, may have the “optimum” crude protein levels for ruminants, such pastures generally have low grazing preference. Thus, voluntary intakes are low and animal production per head is about half that of animals on a high legume diet. Furthermore, animal production per hectare for grass dominant pasture with about 16% CP will be unsatisfactory because the pasture yield will only be about half that produced by a pasture where the grass has a CP of 25%. This is because temperate grasses require >4.0% N in their leaf DM for maximum photosynthesis (Peri et al., 2002b) and grass leaf with a CP of 16% contains only 2.6% N (16% CP/6.25). Such swards display obvious N deficiency with yellow/green leaves and low vigour. There is no obvious solution to this dilemma. Perennial grasses and herbs with reduced critical leaf N content (e.g. =3% N rather than >4%) may be developed in future. In the mean time high sugar grasses will not solve the problem. High energy supplements may help to balance ruminant diets but their cost is unlikely to be economically viable for unsubsidised meat production.

New Zealand pastoral farming must therefore get back to basics. It must ensure the lime, superphosphate, rain (+ irrigation) and sunlight reaching the land is used with maximum efficiency for carbon fixation (photosynthesis) and nitrogen fixation by legumes. The high rate of N fertilizer required to achieve maximum productivity from grass dominant pastures is unlikely to be affordable for a sustainable, unsubsidised pastoral industry.

Problems associated with intensification
Increased pastoral production will result in increased livestock carrying capacities. This means the challenges to mitigate issues of pugging and soil compaction, losses of N and P from the soil profile and potential eutrophication of waterways and NH₃ volatilization will need more urgent attention.

Eutrophication of waterways has lead to nutrient application caps in some regions. The use of riparian buffers and adequate fencing to prevent animals accessing waterways is essential. There is potential for multiple species riparian vegetation buffers which allow plantings of strips of ungrazed deep rooted pastoral plants (e.g. lucerne) surrounding waterways to capture excess N at depth. This forage may then be cut, conserved and fed elsewhere. Trees closer to the waterways improve the habitat for aquatic life and create wildlife corridors. Furthermore, >30% of New Zealand’s total greenhouse gas emissions are N₂O, predominately from urine patches, and recent work has shown that nitrification inhibitors can reduce total N₂O emissions from urine patches by about 70% (Di et al., 2007).

Most of the following mitigation strategies are currently employed but much more general adoption of these will be essential if significant progress is to be achieved. Examples of these strategies are cutting and carrying of winter forages to reduce soil compaction on sensitive land. Animals may be housed in winter and/or feeding out may occur on less fertile paddocks rather than where feed was sourced. This increases costs but provides opportunities for more efficient distribution of the nutrients in effluent across specific targeted areas of the farm.

Farm nutrient budgets
Farm nutrient budgets for individual paddocks are likely to be developed with greater precision. Maintenance fertilizer applications can then make allowances for nutrients transferred between different areas. However, if such measures are unsuccessful on some soil types stocking rates may have to be restricted. For instance, in the past, stocking rates of between 2 and 3 Jersey cows/ha on self contained, family dairy farms may have been sustainable. Such farms relied completely on legumes for their N inputs and little feed was bought in. Modern larger properties use up to 200 kg N /ha on the area adjacent to the milking shed. This area of pasture is known as the "milking platform" and all young and dry cows not in milk are grazed elsewhere. Maize silage and other supplements are also bought in to feed to the milking herd. This may result in stocking rates of 4 cows/ha on the milking platform pasture which exceeds the physical and chemical capacity of the land to absorb the increased treading and nutrient load.

Adjustment of legislation
Apart from adjustment to high country Crown lease properties by Tenure Review (see section 4) there is unlikely to be major change in land tenure law, rural subsidy policy, or biosecurity regulations in New Zealand. The current (2009) centre right government may relax some regulations relating to the Resource Management Act which may affect the individual rights of farm owners to develop their properties. They may also relax current regulations to allow foreign financiers to purchase New Zealand farmland. However such developments are still likely to be controlled by strong environmental legislation.

Legislation to protect New Zealand’s "Clean green image" is likely to be strengthened and laws relating to environmental pollution issues are likely to be enforced more vigorously in the future. This is likely to result in more stringent controls on the use of nitrogen fertilizers, the spreading of effluent, and encouragement to plant riparian strips within fenced off waterways, particularly in dairying regions. Tree planting within steep erodible hill pastures may become obligatory and stocking rate limits on intensive dairy pastures may need to be introduced but as yet none of these measures have been publicly debated.

Farmers are impatiently waiting (2009) for definite legislation which will allow them to participate in the "Carbon Market". With about half of New Zealand's greenhouse gases calculated to come from livestock emissions pastoral farmers require strong market certainty regarding various mitigation measures which they may employ. Carbon sequestration by forest tree planting on less productive farmland is an obvious opportunity which is delayed pending legislative guidance. Current legislation will implement an emissions trading scheme in 2010 but agriculture is currently exempt until 2015.

Social organization
New Zealand social organization in relation to its pastoral industries is unlikely to change radically in the next few decades. There are however some rural population reduction trends which may lead to less precise pasture management. As farms become larger, labour may be substituted with increased mechanisation on large scale properties and managers may prefer to use simple pasture mixtures which are most easily managed. This may result in limited uptake of new pasture technologies which require specific special management regimes.

Pasture plant improvement
Plant breeding programmes should focus on developing plants and animals with increased N use efficiency and increased soluble carbohydrates and lipids. This approach should focus on temperate plants that have a lower N requirement for optimal growth so that the N concentration in urine is reduced. The need for N fertilizer and pure legume pastures may then be avoided. Work is proceeding on increasing the soluble carbohydrates in grasses (see below) but results to date are ambiguous at the animal scale and there has been little publicity regarding the prospect of fixing more carbon per unit of N in C₃ grasses.

Animal breeding programmes aiming to increase the rate of conversion of pasture into saleable animal products are making progress. For example, the recent increases in New Zealand lamb production from significantly reduced ewe numbers is partly attributable to advances in animal breeding, with an emphasis on fecundity and meat production.

New Zealand farmers are familiar with current perennial ryegrass cultivars, their wild and novel endophyte options and the range of white clover cultivars available. The use of this plant material for future plant breeding of these dominant pastoral species, through either conventional and/or genetic technologies may be limited by the lack of genetic variability in highly developed lines (e.g. perennial ryegrass). Market resistance to genetic technologies (both trans- and cisgenic applications) in the food chain is strong in New Zealand and in some high value export markets. This presents a dilemma for science policy and research fund allocation. On one hand New Zealand does not wish to neglect new genetic technologies but there is a risk that these products may never be accepted for inclusion in the food chain by the end consumer. Furthermore, there may be a large opportunity cost in funding genetic technologies rather than concentrating on plant and animal improvement using traditional techniques.

The introduction of pasture species, which show improved production and persistence to the industry standard perennial ryegrass/white clover mix in some environments, can fail to be exploited by rural industry in New Zealand despite the well developed information extension structure. A current example is Caucasian clover which has shown promise for long term production and persistence in montane and lowland pastoral systems. However, it has slow establishment caused by higher thermal time requirements for leaf development in its seedlings compared with white clover (Black et al., 2006). This has meant the species was often suppressed by vigorous perennial ryegrass seedlings when mixtures were established. It is now recommended that Caucasian clover is established as a monoculture or with a low sowing rate of a forage cover crop such as rape. It can then establish and develop its taproot and rhizome system without competition from a companion grass. Once the Caucasian clover is established perennial grass can be oversown. However, now the establishment is understood and recommendations can be made with confidence, the seed is difficult to obtain.

The success of fast establishing perennial ryegrass/white clover pastures means farmers can be impatient with such new species that may establish more slowly. The need to manage speciality pastures with more care can make changes required from the standard ryegrass/white clover management frustrating. Also, the dominant use of pasture seeds premixed by seed companies has led to almost universal use of high seeding rates of ryegrass (>20 kg/ha) which tend to suppress most other species including weeds but do not help the promotion of alternative herbage species. A lack of explanation of the growth habits, peak production periods, management requirements for optimum production and persistence, changes in quality between vegetative and reproductive growth etc. can hinder uptake of other species which may be better adapted for specific purposes than perennial ryegrass and white clover.

Clearly, opportunities exist for new pasture species to fill specific niches but current structures in rural industries require modification before successful adoption is likely.

High sugar grasses
Several perennial ryegrass cultivars bred for high water soluble carbohydrates (WSC) overseas are currently available in New Zealand. These high sugar grasses are promoted for their ability to change the carbon and nitrogen ratio in the rumen thus increasing animal production through improved N utilisation and result in reduced urinary N concentrations. However, recent reviews (e.g. Edwards et al., 2007) report inconsistency in water soluble carbohydrate levels when grown under New Zealand conditions. Genotype x environment interactions were proposed as the cause of variation in trait expression and plant breeders are currently selecting for lines suited to the New Zealand environment. However, the level of increases required to see a response in N utilisation in New Zealand’s intensive grazing systems (100-200 g WSC/kg DM), has not been seen in current material. Equally, the transfer of any benefits from plant to animal performance has been inconsistent.

Seed production in New Zealand
New Zealand is almost self sufficient in herbage seed production with ryegrass and white clover being the main species. New Zealand is the world’s largest producer of white clover seed. With its suitable soils and climate, Canterbury produces more than two thirds of New Zealand’s herbage seeds. Yields are high by world standards with many growers producing >2.0 t/ha of white clover seed in favourable seasons. Apart from species for local consumption New Zealand also produces a wide range of herbage and vegetable seeds for niche markets overseas.

Most of the lucerne and annual clover seed (e.g. subterranean, balansa) is imported from Australia. In recent years seed supply of some annual clover seed has been compromised by Australian droughts and the reliability of seed supply for NZ farmers has been questioned. However, local production of seed from these species is problematic. For example, the technology for harvesting subterranean clover seed from burrs which mature below the soil surface needs further investigation. Strict import and biosecurity regulations mean new species introduction will only be permitted if it can be proved the species will not become invasive.

Initiating a New Zealand cultivar evaluation scheme to evaluate all new cultivars (both imported and locally bred) to test their suitability for local environments would be beneficial to the agricultural industry. Sociability of grasses with legumes and their persistence in grazed pastures should be essential for such a scheme.

Better integration of forages into farming systems
Within given farming systems, greater yields may be achieved by growing a winter active annual such as kale followed by a summer active annual (e.g. maize) but this strategy is likely to require high fertilizer inputs. Currently a collaborative project between research organizations has the objective of producing 40 t DM/ha/yr using this double cropping concept. However, while the 40 t DM/ha objective may be theoretically achievable the nutritive value of the dry matter produced is likely to be deficient in metabolisable energy and crude protein (also see section 5).

Improvements in seedbed preparation and establishment practices used by farmers and their contractors are likely to have the biggest impact on improving integration of forage crops into pastoral systems. Farmers who experience crop failures (see section 5) whether forage crops or alternative pasture species, are unlikely to invest capital into those species again as they are then perceived to be difficult to establish and have increased likelihood of failure.

Pasture rehabilitation
Pasture rehabilitation is driven by potential economic returns. Currently, average pasture renewal intervals exceed 10 years on many farms. Degradation from overgrazing at the farm scale is monitored by individual farmers with increasing guidance and direction from regional councils. In most cases pasture rehabilitation is required after erosion events following significant rainfall. Strategic tree planting is favoured to mitigate future events.

Weed control
With pressures, both economic and environmentally driven, to reduce use of agricultural chemicals the use of goats for woody weed control may gain favour (also see section 5).

Climate change
Salinger (2003) predicted that the impacts of future climate change would result in more rain on the west coast of New Zealand, while eastern areas would be drier and warmer but with greater variability. These predictions will place further physiological limitations on pasture production. Farmers may need to learn how to manage a wider range of pasture species and farming systems will have to be modified to accommodate increased drought frequency in the east and more intense rainfall events and greater total precipitation in western regions.

Summer-moist regions
Increased mean annual temperatures would result in southerly migration of C₄ grasses which currently are limited to warmer regions such as Northland and frost free areas further south. Pest and disease prevalence would also increase. Temperature increases may also increase the number of life cycles that major pasture pests complete in a year. The combination of warmer temperatures and more rainfall in western districts will increase humidity in canopies and fungal disease prevalence could increase. The cost effectiveness of pasture pest and disease control measures will be a major limitation if commodity prices are insufficient to justify applications. Pasture growth rates will increase during winter but warmer summer temperatures will stress some temperate pasture species such as perennial ryegrass. This will require greater use of more drought tolerant species with higher optimum temperatures for growth such as tall fescue, but it will need to be infected with an effective novel endophyte to ensure persistence.

Summer-dry regions
The area of the east coast regions that is subjected to regular prolonged periods of summer/autumn soil moisture deficit are predicted to increase from the current ~3.0 M ha, through climate change. The most commonly sown pasture legume in these areas is still white clover even though it is ill adapted to summer drought. If droughts become more prolonged, and more frequent, production and persistence from white clover will be even less reliable. Leading farmers will show greater reliance on annual pasture species such as subterranean clover and deep rooted perennials such as lucerne.

New Zealand has well developed technologies for grazing lucerne with sheep and, to a lesser extent, cattle. The best advice for dryland farmers is that they should grow lucerne wherever conditions allow and should plant it on the best soils on their properties. Australia leads the world in annual clover research and there is opportunity for New Zealand farmers to adapt Australian technology to their local conditions. Improved management to increase the production of resident (>50 year old) cultivars of subterranean clover is currently being promoted. This in combination with the introduction of the best adapted modern cultivars and adoption of appropriate management strategies should enable dryland livestock farmers to at least maintain their current productivity if soil moisture regimes become more adverse.

The special feature of annual legumes over perennial legumes is their much faster growth rates in the cool season. Dryland farmers can exploit this annual legume productivity in late winter/spring (August to November) for ewe lactation. Twin lambs suckling from ewes grazing a pasture with 50% legume on offer can grow at 350-400 g/head/d before weaning at 90-100 days of age. Ideally all lambs should be sold from drought prone farms by the end of December. The basic technology for dryland pastoral farming is being applied by leading farmers and increasing drought experiences may hasten adoption rates of current best practice. Further advances are anticipated through the introduction of top flowering annual legumes from Australia to complement subterranean clover.

Current work in New Zealand with balansa and arrowleaf clovers suggests they may have a place in dryland pastoral systems. Gland clover (Trifolium glanduliferum) is an early flowering recent introduction which may also complement subterranean clover on sites with <500 mm effective rainfall (e.g. sunny north and northwest hill faces where evapotranspiration is extreme). Gland clover is one of the few annual legumes which is resistant to red legged earth mite (Halotydeus destructor). This major pest of annual legumes is likely to become more troublesome as conditions become warmer and drier.

Climate change predictions for a general increase in temperature will result in higher temperatures in high country regions and extend the perceived altitudinal limit to pastoral development. This limit is currently considered to be 900 m but improved pastures at higher altitudes may be viable in future. Perennial legumes such as Caucasian clover may have a role in such environments.

In conclusion, some of the issues and mitigation strategies discussed in this section are already standard practice for New Zealand’s “top” farmers. Nationally, the biggest shift in future productivity is likely to be achieved by uptake of existing “best practice” strategies by other farmers. This will require the advice and support of the entire agriculture industry (including research organizations, education providers, contractors, commercial field officers and extension staff) to transfer current knowledge onto farms. These practices will then be integrated into existing systems to maintain and enhance efficiency and ecologically sustainable pastoral agriculture.

There are several Government and University based pastoral research programmes in New Zealand. The dominant crown research institute is AgResearch. In addition, Massey University in the North Island and Lincoln University in the South Island provide degree-based agricultural teaching and research.

AgResearch
Website: www.agresearch.co.nz/

Summary. AgResearch is a crown-owned research institute of approximately 1 000 staff, 650 of whom are research and development staff. Annual revenue is over NZ$ 150 M.

Their mission is focused around three complementary objectives:

1. To underpin the New Zealand pastoral sector’s sustainability and profitability
2. To establish a range of biotechnologies and systems in New Zealand
3. To export AgResearch biotechnologies and systems where appropriate

Staff are mainly located on one of four campuses (Hamilton, Palmerston North, Lincoln and Invermay). 

Summary of activities relevant to the dairy sector. The Dairy sector in New Zealand is served by several key research providers, including Fonterra’s own research units, DairyNZ, LIC and some universities. AgResearch seeks to complement these other institutes, not compete in most cases.  Almost all activity within AgResearch is relevant to the dairy sector to some extent. A brief summary by section is shown in Table 14. In addition to these R&D capabilities, AgResearch has one dairy farm in the Waikato (at Ruakura), with another under development (at Tokanui) and one dairy farm in the Manawatu (at Flock House).

Strategic intent. AgResearch has developed a comprehensive strategic plan for improving the pastoral sector of New Zealand through research and development, called 2020 Science. The Dairy sector has a significant place in the strategic direction of AgResearch. Their current plans for research for the dairy industry are encapsulated in Goal 1 of the 2020 science implementation plans. The objective of Goal 1 is:

“by 2020, the net economic/export value of the NZ dairy sector will be doubled while halving (reducing) adverse environmental impacts (to acceptable international standards), through achieving productivity gains, sustainable intensification, reducing emissions to air and water, developing new, high-value products and enabling technologies and services (all compared to 2005 levels)”.

Partner organizations. AgResearch sections work with DairyNZ (in the areas of farm systems, forage and the environment), Fonterra (environment, forage development through its subsidiary Vialactia Biosciences), Massey University, LIC and many dairy processors (including Fonterra) in the development of processed dairy products. Investors include Pastoral21, FRST, DairyNZ and dairy companies.

DairyNZ Ltd, Hamilton
Website: www.dairynz.co.nz/

DairyNZ is the single dairy industry-good body owned by and operated on behalf of all of New Zealand’s dairy farmers. The organization is based at Newstead with two adjacent research farms. Other research staff are based in Northland, Taranaki and Canterbury, also with access to major research farm facilities.

The Science Programme is managed by;

Chief Scientist – Eric Hillerton (Email: Eric.hillerton@dairynz.co.nz)

Leader of Animals Research - John Roche

Leader of Feed/Farm Systems Research - Dave Clark

The whole research team comprises 25 post-doctoral scientists and 75 technical, support and farm staff. More than 55 research projects are commissioned but the major effort is in 6 key areas. These are in;

• Feed Conversion Efficiency (Garry Waghorn and Kevin Macdonald)
• Lactation Management Strategies (John Roche)
• Novel tools to prevent mastitis in dairy cows (Jane Lacy-Hulbert)
• Improved cow fertility by novel nutritional strategies and epigenetics (Susanne Meier)
• Animal welfare (Gwyn Verkerk)
• Dairy systems for environmental protection (Dave Clark).

Lincoln University
Website: http://www.lincoln.ac.nz/

Massey University
Website: http://www.massey.ac.nz/

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9. Contacts

Derrick currently teaches a range of undergraduate and postgraduate subjects and supervises PhD, Masters and Honours students on annual crop production and pasture science. His current research priority is in environmental influences on the growth and development of perennial and annual plant species. Work specifically focuses on: Dryland pastures; lucerne, annual legumes, cocksfoot, nitrogen management, water relations, pasture growth and development Cereal crops; wheat, barley, oats - quality and quantity of production Dr. Derrick J. Moot Professor of Plant Science Department of Agricultural Sciences Faculty of Agriculture and Life Sciences P.O. Box 84 Lincoln University Canterbury 7647 New Zealand Ph: +64 3 325 2811 Fax: +64 3 325 3880 Email: Derrick.Moot@lincoln.ac.nz

Anna is involved in pasture research which focuses on production and persistence of annual and perennial pasture species in dryland environments. This includes: Explaining the effects of temperature, water and nitrogen on the production of pasture species with physiologically based unifying relationships Explaining differences in animal production caused by differences in the quantity, quality and persistence of pasture on offer Dr. Annamaria Mills Postdoctoral Fellow in Plant Science Department of Agricultural Sciences Faculty of Agriculture and Life Sciences P.O. Box 84 Lincoln University Canterbury 7647 New Zealand Ph: +64 3 325 2811 Fax: +64 3 325 3880 Email: Anna.Mills@lincoln.ac.nz

Since his retirement Dick has continued to work on an almost full time basis focussing on extension. Primarily his work involves advising and promoting the use of annual legumes in dryland farming systems. Mr R.J. Lucas Senior Lecturer in Plant Science (Retired) Department of Agricultural Sciences Faculty of Agriculture and Life Sciences P.O. Box 84 Lincoln University Canterbury 7647 New Zealand Ph: +64 3 325 2811 Fax: +64 3 325 3880 Email: Dick.Lucas@lincoln.ac.nz

Warwick currently teaches at both undergraduate and postgraduate levels and is involved in the supervision of students at PhD, Masters and Honours levels. His current research interests include: Agronomy of herbage seeds, cereals, forage brassicas and greenfeeds Apical development of ryegrass cultivars in relation to herbage yield, grazing preference and seed yield. Effluent disposal Dr Warwick Scott Senior Lecturer in Plant Science Department of Agricultural Sciences Faculty of Agriculture and Life Sciences P.O. Box 84 Lincoln University Canterbury 7647 New Zealand Ph: +64 3 325 2811 Fax: +64 3 325 3880 Email: Warwick.Scott@lincoln.ac.nz

[The profile was drafted in the period March to September 2009 and edited by J.M. Suttie and S.G. Reynolds in October 2009].