Pozo Propuesto Perfil tipo J

The most commonly sown pasture in New Zealand is a mixture of perennial ryegrass (Lolium

perenne L.) and white clover (Trifolium repens L.). While this mixture is suitable for summer-

moist or irrigated pastures, they are less persistent and productive in dryland farming systems subject to periodic water stress in the late spring and summer period (Mills and Moot, 2010). Brock (2006) indicated that the shallow rooting species white clover needed rainfall of 40 mm/month for persistence and 60 mm/month for performance; otherwise without irrigation white clover should not be considered. Further, Knowles et al. (2003) concluded that white clover is generally not tolerant of water deficit conditions, with poor post-drought recovery. Thus, there is a need to consider and evaluate alternative grass-legume combinations, that are more persistence and productive, under dryland conditions.

The annual legume, subterranean clover (Trifolium subterraneum L.), has considerable potential as an alternative to white clover on dryland farms (< 800 mm/annum). Subterranean clover avoids water deficit conditions by growing actively in late winter and spring, flowering and producing seeds before the onset of summer water deficit, and re-establishing from seeds during autumn. Mills and Moot (2010) concluded that in dryland pastures in Canterbury subterranean clover-cocksfoot had greater dry matter production over a seven year period than other mixtures, including perennial ryegrass-white clover.

A further alternative approach to white clover is to use a more water deficit tolerant perennial legume such as strawberry clover. The taproot of strawberry clover generally persists longer than that of white clover (Frame, 2000). Further, Hofmann et al. (2007) indicated strawberry clover showed greater water deficit resistance in a number of key parameters, including water status, photosynthesis and transpiration compared to white clover. However, Hofmann et al. (2007) indicated that a lack of nodal rooting in strawberry clover may be a limitation on the persistence of strawberry clover and stressed the need to examine the production and persistence of strawberry clover under grazing conditions.

Tall fescue is a deep-rooted, perennial grass that may be a useful alternative to perennial ryegrass under dryland conditions (Stephenson and Posler, 1988; Charlton and Stewart, 2006). Tall fescue is noted for its high heat tolerance leading to improved summer growth (Reed, 1996), and tolerance of a range of insect species such as grass grub, porina (Wiseana spp.) (Bourner et al., 1996) and Argentine stem weevil(Popay and Ball, 1998). Tall fescue cultivars have been classified into Continental (summer-active) and Mediterranean (winter-active) types based on their seasonal growth patterns (Stewart and Charlton, 2003; Hand et al., 2010). The summer-active Continental type, has contributed the majority of temperate cultivated germplasm and grows vigorously in summer and moderately in winter (Stewart and Charlton, 2003). Conversely, Mediterranean cultivars grow more strongly in the cool season and have limited summer growth due to dormancy in response to increasing day length and probably high temperatures (Villiers, 1975; Ofir and Kerem, 1982). This may enable grass plants to escape summer water deficit andinitiate autumn regrowth in response to decreasing day length and lower temperatures (Malinowski et al., 2005). However, few studies have measured pasture growth of Continental and Mediterranean cultivars under Australasian conditions or considered interactions with associated legumes. The study by Tharmaraj et al. (2008) in south-western Victoria, Australia showed that the winter-active cultivar Flecha had similar overall seasonal

distribution of forage supply and total annual yield compared to the control ryegrass-white clover pasture, but that the summer-active cultivar Advance had significantly greater herbage accumulation compared to the perennial ryegrass-white clover pasture during summer.

In evaluating pasture grass species, it is important to consider how the grass and legume species interact in mixtures (Harris et al., 1981). Grass competition plays an important role in regulating establishment, growth and persistence of annual and perennial legumes in mixtures and seasonal patterns of growth of grass may play a key role in this (Cherney et al., 1986). It is possible that Mediterranean tall fescue cultivars, which begin growth earlier in spring, may compete more strongly with annual legumes such as subterranean clover than Continental tall fescue cultivar. However, the establishment of the annual legume may be better in autumn when grown with Mediterranean tall fescue due to the slow growth of grass following dormancy providing greater opportunity for recruitment of new plants. Further, Mediterranean tall fescue may compete less strongly than Continental tall fescue with perennial legumes during water stress periods during summer.

The performance of grass-legume mixtures under dryland conditions is also determined by levels of macronutrients critical for legume growth and persistence, such as phosphorus (P) and sulphur (S) (Smith et al., 1998). Tall fescue is generally regarded as high fertility species (Charlton and Stewart, 2006); however, there is little data on response to P and S fertility under New Zealand condition. White clover is noted for being responsive to both P and S fertility. Dodd and Orr (1995) showed that the annual clover species serradella,hairy bird's-foot trefoil and subterranean clover were able to maintain high levels of growth at low P levels relative to their potential at high P, and were thus suited to low P fertility soils. Further, Dodd and Orr (1995) noted strawberry clover as responsive to P and S as the perennial legume red clover.

This study reports pasture growth and composition over two years for a dryland grass-clover pasture in Canterbury, New Zealand maintained under intensive sheep grazing. The specific

objective of the current study was quantify the interactive effects of tall fescue cultivar (Continental, cultivar Advance, versus Mediterranean, cultivar Flecha), sown clover species (subterranean clover versus a combination of white and strawberry clover) and soil fertility (high P and S fertilizer versus low fertilizer P and S) on annual and seasonal DM production, botanical composition, plant density and plant morphology. The effects on pasture nutritive value and sheep liveweight gain of the same pastures are considered in Chapter 4.