This study sought to define the optimum defoliation interval for Lolium perenne, with the maximum interval being determined by the onset of senescence, as reflected by the number of fully expanded leaves, and the minimum interval set by the replenishment of water-soluble carbohydrates (WSCs).In a glasshouse set at 13''C/23''C night/day tem-ptr^^ture and at a plant spacing of 94 m""-(3290 tillers m'-). the accumulation of dry matter against leaf number and days was exponential to the fourleaf stage of the regrowth cycle. Senescence commenced at the 3 5-leaf stage.WSCs in roots, stubble and leaf showed a very significant linear relationship with leaf number. Levels of WSCs in leaves were restored to predefoliation values by the one-leaf stage, after which WSCs accumulated preferentially in the stubble, rising to 22% at the four-leaf stage.Regrowth after 6 d was significantly greater for plants defoliated at the three-leaf stage than at the one-leaf stage, but this difference disappeared at the end of the regrowth cycle. This questions the importance of WSCs in determining the yield of ryegrass under normal rotational grazing management.Regrowth at 6 d was related positively to stubble WSCs (r^ = 0-66) and to stubble DM per tiller

The object of this study was to determine the importance of frequency and height of defoliation on regrowth potential of Lolium perenne. Defoliation interval was based on stage of the regrowth cycle, as indicated by leaves per tiller.Simulated swards of Lolium perenne cv Yatsyn were grown as individual plants in a glasshouse kept at a day/night temperature of 25°C/15''C.Treatments imposed were defoliation at 2, 5 or 12 cm residual height, and low and high water soluble carbohydrate (WSC) level obtained by varying defoliation interval, i.e. defoliating at the I-leaf or 3-leaf stage of the regrowth cycle. Regrowth after freqtient short defoliations was only 65% of the less frequently defoliated plants taken over the full regrowth cycle. This was associated with a lower stubble WSC content (2-15 vs 17-5% in stubble) and a twenty-seven-fold difference in the amount of WSC in the stubble per plant. This difference in total WSC was a combined effect of more and heavier tillers and higher WSC content in stubble of plants defoliated less frequently at the end of the regrowth cycle. The regrowth of plants with WSC levels depleted by frequent defoliation when defoliated at 2 cm was significantly below that of those defoliated at 5 and 12 cm.The results indicate the desirability of defoliating plants at the 3-leaf stage of the regrowth cycle. This not only allows the full regrowth potential to be expressed in that growth cycle, but also in the next cycle, by allowing the replenishment of WSC reserves and optimizing tiller status. The potential to regrow appears then to be based more on the total CofTespondence: W. J. Fulker^on. NSW Agriculture, Wollnngbar Agriculwral Institute. Woliongbar, NSW 2477, Australia. amount of WSC than the proportion of WSC in stubble.

Summary. On the subtropical north coast of New South Wales, Australia, kikuyu grass (Pennisetum clandestinum), biennial ryegrass (Lolium multiflorum) and mixed perennial ryegrass (Lolium perenne)–white clover (Trifolium repens) pastures grazed by dairy cows were plucked pregrazing to simulated grazing height, every 2 weeks for 2 years to determine seasonal changes in various nutrients and in sacco organic matter and nitrogen (N) degradability. Changes in nutrients during regrowth were determined in the ryegrass component of a mixed perennial ryegrass–white clover pasture by sequentially cutting pasture at 3- or 4-day intervals to 5 cm stubble height and non-structural carbohydrates in kikuyu by cutting at 4-day intervals in February–March. There was a significant effect of season on water-soluble carbohydrate (WSC) and crude protein (CP) content of perennial ryegrass with regrowth time, resulting in an 8-fold fall in the CP : WSC ratio from the 1 to 3 leaves/tiller stage of regrowth in mid winter, a 2-fold difference in mid spring but with no discernible difference in late spring. The metabolisable energy (ME) values for biennial ryegrass exceeded 11.9 MJ/kg dry matter (DM) from July to September and then fell markedly to <10 MJ/kg DM in November, coinciding with reproductive development. In perennial ryegrass–white clover pastures, mean ME was above 11 MJ/kg DM from May to September, but fell to < 9 MJ/kg DM in December while in kikuyu, the mean ME, over the recognised growing season, was 8.5 MJ/kg DM but in winter it was 9.5 MJ/kg DM. Fibre content in all pasture types showed a significant seasonal trend with the content of acid detergent fibre (ADF) in biennial ryegrass at 17% from May to August while the mean neutral detergent fibre (NDF) content was 37%. In perennial ryegrass–white clover, the mean ADF was <21% from May to August. The NDF content of kikuyu grass was about 60% during the growing season but 40% in winter. The calcium (Ca) : phosphorus (P) ratio in perennial ryegrass rose from <1 : 1 at the 1 leaf/tiller stage to 2.2 : 1 at the 3 leaves/tiller stage of regrowth due to a simultaneous fall in P and a rise in Ca. A fall in potassium (K) and a rise in magnesium (Mg) and Ca content in perennial ryegrass gave a very significant linear fall in K/(Mg + Ca), on a percentage basis, from 8 at the 1 leaf/tiller stage of regrowth, to 2.5 at the 3 leaves/tiller stage of regrowth. In kikuyu, the level of P changed significantly with season falling as the species became dormant. A fall in P and a rise in Ca content resulted in a high Ca : P ratio (2.5 : 1) in spring. The findings of this study give some insight into the reason why the content of various nutrients change in pasture and the implication of this for providing a balanced diet to dairy cows. A knowledge of these changes should provide the opportunity to balance nutrients in pasture by adjusting time of grazing and/or providing supplements of appropriate quality.

This plot cut study, conducted on the subtropical north coast of New South Wales, evaluated the effect of defoliation interval, seeding rate and application of nitrogen and lime on production and survival over summer of a Lolium perenne/Trifolium repens pasture. There was a 117% or 12 781 kg DM/ha difference in DM yield between the worst and best treatment combinations over the 17 month period of the study. The best treatment combination for yield also gave the highest rate of ryegrass survival and lowest levels of 'summer grass' ingression over the first summer. Defoliation at 4 weeks or 'when ready' (before onset of senescence, 'lodging' or rust), compared to at 2 weeks, increased DM yield by 18 and 32% in year 1 and 41 and 59% in year 2 respectively. The larger difference in year 2 was primarily due to a greater ingression of 'summer grass' (winter dormant) and a lower survival of ryegrass plants over the first summer in the most frequently cut plots. The lower root DM in summer at the more frequent cutting interval may have been one factor responsible for the defoliation effect. DM yields of a 'clover dominant' sward (nil N except at sowing and 8 kg ryegrass/ha; clover = 53%) was 85% in year 1 and 50% in year 2 (up to August) of that of a 'ryegrass dominant' sward (100 kg urea ha-1 mo-1 and 35 kg ryegrass/ha; clover = 8%). The lower yield of the 'clover dominant' pasture in year 2 was partly due to a greater level of 'summer grass' infestation. Application of N increased plant survival over summer, but under grazing, many plants may have been lost through sod pulling by stock, as roots were more restricted to the surface. Application of lime increased DM yield in both years.

A grazing study was conducted, over a 3-year period (1997–99), on the subtropical north coast of New South Wales, Australia, to compare the yield of prairie grass (Bromus willdenowii cv. Matua), tall fescue (Festuca arundinacea cv. Vulcan) and perennial ryegrass (Lolium perenne cv. Yatsyn), on a well-drained red krasnozem soil at Wollongbar Agricultural Research Institute (WAI) and on a heavy clay soil at Casino. The effect of grazing interval (equivalent to the time taken to regrow 1.5, 2.5 or 4 leaves/tiller) in spring, and forage quality of prairie grass in winter and spring was also assessed. At both sites, the dry matter (DM) yields of prairie grass over the establishment year and in year 2 were significantly (P<0.001) higher than for the other 2 grass species (mean for 2 years over the 2 sites was 23.8, 8.9 and 7.7 t DM/ha for prairie grass, ryegrass and tall fescue, respectively). In year 3, there was no production of tall fescue or ryegrass at the WAI site while prairie grass produced 11.3 t DM/ha although this was obtained from natural seedling recruitment after the sward was sprayed with a herbicide in February of that year. At the Casino site, ryegrass and tall fescue still made substantial growth in year 3 (3.1 and 2.1 t DM/ha for ryegrass and tall fescue, respectively) but this was significantly below the yields of prairie grass (5.5 t DM/ha). More frequent grazing of prairie grass in spring (equivalent to 1.5 leaves/tiller of regrowth) led to significantly (P<0.05) less plants surviving summer and less seedling recruitment in the following autumn. The annual yield of the 1.5 leaf treatment was significantly (P<0.05) lower than the remaining treatments but only in the third year of the study. Analysis of prairie grass forage samples, taken in June (vegetative sward) and November (reproductive sward), gave magnesium values of less than 0.2% DM which is below the concentration found in ryegrass and that recommended for dairy cattle. The Ca : P and K : (Ca + Mg) ratios in prairie grass improved, as a forage for dairy cows, with regrowth time up to 5 leaves/tiller. Metabolisable energy remained constant with regrowth time in June at 10.8 MJ/kg DM but fell significantly in November from 10.7 MJ/kg DM, immediately post-grazing, to 9.2 MJ/kg DM at the 4.5 leaves/tiller stage of regrowth. In contrast to observations in ryegrass, the water-soluble carbohydrate content of forage samples of prairie grass taken in November showed a substantial increase with regrowth time to over 12% DM at the 3 leaves/tiller stage of regrowth. The high productivity and forage quality of prairie grass obtained over a 3-year period suggests this grass species could be a suitable temperate perennial grass for subtropical dairy pastures. An appropriately long grazing interval in spring seems critical to optimise plant survival over summer and for adequate seed set for seedling recruitment the following autumn. If summer weeds and/or grasses invade to a significant extent, the large seedbank of prairie grass provides the opportunity to spray out the pasture in summer and rely on seedling recruitment to establish a new sward in autumn. The forage quality of prairie grass in winter and spring is similar to perennial ryegrass but the magnesium levels are substantially lower and stock grazing this type of pasture for extended periods would need to be supplemented with this mineral.