Grazing management and pasture production of tall fescue-legume mixtures in dryland pastures

Abstract

Pasture production and composition and liveweight gain of sheep grazing tall fescue-clover and perennial ryegrass-clover dryland pastures at Lincoln, Canterbury was examined in four experiments from May 2008 to December 2010. Four objectives were identified to (i) quantify the pasture production, growth, persistence, composition, (ii) pasture nutritive value and liveweight gain of sheep grazed cultivars of tall fescue, white, strawberry and subterranean clover at high and low P and S fertility, to determine the (iii) effect of time of grazing in autumn on subterranean clover growth was determined, and (iv) effect of spring defoliation management on tall fescue cultivars and perennial ryegrass pastures grown with white and strawberry clover. Experiment 1 examined 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 morphology. Annual DM production was greater in Advance (7790 kg DM/ha) than Flecha (6871 kg DM/ha) in year 1 and Flecha (8367 kg DM/ha) than CA (7547 kg DM/ha) in year 2. Annual DM production of the legume component was greater in subterranean clover pastures than perennial clover pastures in both year 1 (945kg DM/ha v 539 kg DM/ha) and year 2 (1457kg DM/ha v 1042 kg DM/ha). Survival of strawberry clover in perennial clover pastures was poor with a low percentage (< 1 % DM) in pasture after 2 years. The percentage of clover in pastures was generally greater in Flecha than Advance. Annual DM production was greater at high than low fertility in both year 1 (8734kg DM/ha v 7828 kg DM/ha) and year 2 (7134 kg DM/ha v 6834 kg DM/ha). This primarily reflected greater grass growth at high fertility as legume growth was unaffected by soil fertility. Experiment 2 examined the interactive effects of tall fescue cultivar (Advance versus Flecha) and soil fertility (high P and S fertilizer versus low fertilizer P and S) on pasture nutritive value and liveweight gain of ewes and lambs in spring and ewe hoggets in autumn. Liveweight gain per head of single lambs grazing with lactating ewes (22 ewes/ha) was 284 g/head/day over a 27 day period in spring of year 1. Liveweight gain per head of twin lambs grazing with lactating ewes (25 ewes/ha) was 258 g/head/day over a 60 day period in spring of year 2. Over the total spring period in each year, there was no effect of soil fertility or tall fescue cultivar on liveweight per head or ha of lambs. This occurred despite pasture growth and feed availability being on occasions greater in Flecha than Advance, and at high than low soil fertility. Liveweight gain per head of ewe hoggets (22 ewes/ha) was greater in Flecha (52 g/head/day) than Advance (14 g/head/day) over a 51 day period in autumn of year 1 but greater in Advance (282 g/head/day) than Flecha (197 g/head/day) over a period of 18 days in autumn of year 2. The different cultivar effects between years reflected the availability of feed in response to summer rainfall at the start of the grazing period as well as pasture growth during the grazing period. The clover percentage was average 20% and 31.2% in spring 2008 and 2009, respectively. Experiment 3 examined the effects of grazing subterranean clover at the spade leaf, three trifoliate and six trifoliate leaf stages in autumn on seedling populations, seedling survival and DM production of subterranean clover when grown with Advance and Flecha tall fescue cultivars. Seedling death during grazing was greater at the spade leaf (43%) than the three leaf or six leaf (14%) stage. However, because seedling populations were initially high (1326 plants m2), this high death with early grazing simply killed seedlings that would have died for other reasons; and seedling numbers at the start of winter were similar among treatments (619 plants m2). Spring clover DM production was greater at the spade leaf (2834 kg DM/ha) than three leaf (2573 kg DM/ha) or six leaf stage (2648 kg DM/ha), reflecting greater plant size than any difference in plant population. Delaying grazing until after the three leaf stage will enhance seedling survival when seedling populations are low. Experiment 4 examined DM production, botanical composition, and plant morphology of perennial ryegrass, Advance and Flecha tall fescue pastures grown with strawberry clover and white clover under continuous stocking and rotational grazing in spring. DM production in the establishment phase was greater in perennial ryegrass (1098 kg DM/ha) than Advance (563 kg DM/ha) or Flecha (503 kg DM/ha). In the first full year, DM production was greater in perennial ryegrass (9417 kg DM/ha) and Advance (9928 kg DM/ha) than Flecha (7559 kg DM/ha). Annual DM production of legume was greater in white clover (1638 kg DM/ha) than strawberry clover (670 kg DM/ha). Persistence of strawberry clover was poor with the plant population declining from 145 plants/m² at start to 9 plants/m² after 20 months. Although taproots were larger and lasted longer in strawberry clover than white clover plants, strawberry clover plants had fewer nodal roots, which appeared to limit persistence under grazing. There was no effect of continuous stocking versus rotational grazing on DM production or persistence of white and strawberry clover. The study showed that pastures based on either Continental or Mediterranean tall fescue cultivars are capable of high DM production in dryland pastures in Canterbury, particularly when grown with subterranean clover. These pastures gave high liveweight gain, which would enable lambs to be finished in spring before the onset of summer dry conditions. Under the conditions of this study, there was little detectable effect of tall fescue cultivar on livestock performance, indicating a role of both types of tall fescue for dryland pastures in Canterbury. Strawberry clover persisted poorly under all grazing management, and without breeding for improved nodal root development or revised grazing management guidelines, will not be a suitable legume for dryland pastures.