Regrowth characteristics of lucerne under different systems of grazing management

Abstract

The regrowth characteristics of lucerne (Medicago sativa cv. Hunter River) were measured within an experiment conducted at Lawes, south-eastern Queensland, from 1971 to 1977 (Leach 1979). The experiment included six grazing and three mowing treatments: (1) R32/G4, (2) R32/G16, (3) R44/G4, (4) R44/G16, (5) R56/G4, (6) R40/G8, (7) R36/M, (8) R48/M and (9) R60/M, where R represents the days of rest between grazings (G) or mowings (M) and G the days of grazing after each rest period. These treatments formed cycle lengths of 36, 48 or 60 days, and regrowth experiments were usually undertaken when the ends of two or more defoliation cycles coincided. There were 15 regrowth experiments: experiments 1-9 were conducted over the first 720 days, experiments 10–14 over the next 720 days, and experiment 15 after another 720 days. In experiments 1-9 an initial harvest was made on day 0, and the regrowth was measured after 8 and 24 days. In experiments 10-14 there were harvests on days 0 and 24, and in experiment 15 on days 0 and 14. Amounts of regrowth were more strongly influenced by season and by soil moisture status than by imposed treatments, with final yields differing by up to 10-fold between winter and summer experiments. Seasonal differences in shoot size, and to a lesser extent in shoot numbers, were also much larger than treatment effects within experiments. These results appeared to be a consequence of the grazing and mowing systems being selected from within a recommended range for lucerne, and also of ensuring that moisture equivalent to the long-term average was received each month. Within experiments the yield of regrowth increased as the resting interval between defoliations increased, with a twofold difference between treatment extremes in some experiments. In general, grazing for 16 days led to better regrowth yields than grazing for 4 days which was in turn superior to mowing. Retaining residues after grazing generally increased regrowth, particularly following 16 days of grazing. However, residues greater than 80–100 g m-2 decreased regrowth. Most treatment differences were particularly evident on day 8, which indicated that treatments affected regrowth mainly through the speed of regrowth resumption after grazing or mowing. Although treatment effects on total regrowth yield were attributable to change in both shoot numbers and shoot size, the latter component was usually the more important determinant. Regrowth yield per unit area was maintained by compensating increases in yield per plant, whilst lucerne density fell from an initial 50 plants m-2 to about 30 plants m-2 over the first 3 years, but subsequent losses of lucerne plants led to decreased yields per unit area.

Herbage production and persistence of Puna chicory (Cichorium intybusL.) under grazing management over 4 years

“…1992). Regrowth yield per unit area of lucerne was maintained by compensatory increase in yield per plant even though density has been reported to decline from an initial 50 to about 30 plants/m 2 over the first 3 years, but subsequent losses of plants led to decreased yields per unit area (Leach 1979).…”

The production and utilization of lucerne in New Zealand

“…The very short grazing time as proposed by Iversen (1967) is often difficult to achieve under farm conditions, and its necessity can be questioned on the grounds that when lucerne is defoliated there is a lag phase before the new basal shoot becomes vulnerable to grazing. The length of this lag phase is strongly influenced by the environmental conditions at the time of defoliation (Leach, 1979b) and it is shorter if the crop is more mature at defoliation (Leach, 1968;Janson, 1975a). Janson (1975a) concluded from simulated grazing studies that lucerne in the midvegetative and early bud stage could be defoliated over 14 days with little effect on the regrowth cycle, but at 1% flowering, a 7-day defoliation gave the best regrowth.…”

Development and evaluation of grazing-tolerant alfalfa cultivars: A review

“…Rotational stocking is generally accepted as essential to maintain alfalfa stands and to allow vigorous regrowth and subsequent animal productivity (Leach 1979;Walton et al 1981). The more intensive management required for rotational stocking systems is acceptable to dairy producers.…”

“…Experience from both North America and Australia indicated that creeping-rooted cultivars were variable in their ability to "creep" and regenerate in pastures (Leach 1979;Smith and Bouton 1993) and cultivars and germplasms selected for this trait were not found to be any more grazing tolerant than adaptive, hay-type checks in intensively managed, highly productive pastures in regions with humid conditions, and high summer temperatures (Gramshaw et al 1982;. In many regions of the USA, creeping-rooted cultivars have also been of limited usefulness because of early fall and late spring dormancy and slow regrowth rates (Busbice and Hanson 1969).…”

“…The major factor limiting trait selection for grazing tolerance in alfalfa is the difficulty in developing accurate techniques to select for the many morphological and physiological traits often associated with grazing tolerance such as deep-set crowns (Piskovatski and Stepanova 1981), rhizomatous roots (Piano et al 1996), subsurface budding (Lorenz et al 1982), broad crowns (Kehr et al 1963), prolific and non-synchronous budding (Kaehne 1978;, extended periods of budding (Leach 1979), maintenance of leaf area under grazing (Brummer and Bouton 1992), maintenance of root carbohydrates under grazing (Counce et al 1984;Brummer and Bouton 1992;Smith et al 1992), disease resistance (Lodge 1991;Smith and Bouton1993) and pest resistance (Leach and Clements 1984). Nonetheless, most of the grazing-tolerant cultivars developed in North America prior to 1990 were selected for two traits: broad crowns and/or creeping rootedness (i.e., the ability of new shoots to be initiated from lateral roots) (Heinrichs 1963(Heinrichs , 1978.…”