A rising-plate meter and a single-probe capacitance meter were calibrated on perennial ryegrass swards {cultivars S23. Endura, Melle) over the spring and summer (13 March to 14 September 1981). The swards were rotationally grazed by cattle and from mid-June onwards they were irrigated and cut at 5 cm after grazing to remove rejected herbage. Linear regressions were calculated relating meter readings to herbage dry matter mass as measured by cutting 0-2 mq uadrats to either 18 mm above ground or to ground level.The regression for the rtsing-plate meter was constant over the spring (slope 275 kg DM ha"' cm"'} and again over the summer (slope 385 kg DM ha"' cm"*'). The regression for the capacitance meter changed slightly over the spring (slope 112 to 140 kg DM ha"' unit reading"') and was also constant over the summer (slope 20 3 kg DM ha"' unit reading"'). Correlation coefficients were always above 09 and residual standard deviations ranged from 258-525 in spring up to 636-918 kg DM ha"' in summer. Residual standard deviations were lower with the plate meter than with the capacitance meter and were lower with the ahove-ground cutting height. Neither meter was able to give accurate results with tall rejected herbage containing a build-up of senescent material.Herbage mass below 18 mm was greater on Correspondence and present address: Mr P. Michell, Department of Agricullure. P.O. Box 46. South Launceston. Tasmuniu. Australia 7250. 0142-S242/83/1200-0295S02.00 O I9S3 BlackweM Scientific Publicaiions summer than spring swards. When compared with a ground level cut. cutting above ground underestimated herbage mass on summer relative to spring swards; there was also a tendency to underestimate herbage mass on tall pastures relative to short pastures.There was no evidence of a curved relationship between herbage mass and meter reading with either meter and both meters gave readings related to herbage dry matter mass rather than mass of green herbage or water.
A rising-plate meter was used in a double sampling tecbnique to measure the herbage mass of rotationally grazed perennial ryegrass-white clover swards over a period of 2 years. The meter was calibrated by developing a linear regression between meter reading and herbage dry matter mass as measured by cutting 0-2-m^ quadrats to ground level.There was a strong relationship between meter reading and herbage mass, and correlation coefficients were consistently 0-8 or above. The calibration regression was normally constant for extended periods, especially over the winter and spring. The relationship was more variable over the summer but appeared to follow a pattern that was to some extent repeatable between years. The slope of the regression (kg DM ha~' cm~') was 312 and 267 in the two winters and reached values of 800 and 452 in the two summers. The calibration relationship was adequately described by a linear model over the winter and spring but there was a tendency for a curved relationship in midto late summer.The standard pooled regression found with winter ryegrass-clover swards was not applicable to the more erect prairie grass, and the standard regression overestimated slightly the yield of heavily grazed swards. There was no evidence ofa difference in relationship between irrigated and non-irrigated swards over the summer.The individual meter readings could be used to develop a useful diagrammatic picture of the Correspondence: Mr P, Michell, Mt, Pleasant Laboratories,
Two 20-block farmlets, each of 6.5 ha, were rotationally grazed by milking cows in spring at stocking rates of 1.9 and 3.4 cows/ha to give a low (LGI) or high (HGI) grazing intensity. These grazing intensities were designed to simulate dairy farms with low or high levels of pasture conservation, and resulted in post-grazing residues of2.6 (LGI) and 1.7 (HGI) t/ha DM by late spring. Over summer, the 2 groups of cows continued to graze their respective areas, but spare cows were re-allocated between the groups so that stocking rates were the same at 1.7 cows/ha. The HGI cows produced 1 kg less milk fat (0.79 v. 0.81 kg/day.cow, P> 0.05) in spring (15 October-30 November), but produced significantly (P < 0.05) more milk fat (0.63 v. 0.59 kg/day.cow) and 1.3 kg milk protein (0.44 v. 0.42 kg/day.cow) in summer (1 December-1 February). Despite the higher grazing intensity in spring. there was no difference in intake of pasture or in digestibility of herbage selected by the cows in the two herds. In summer the HGI swards contained less dead herbage (P<0.05) but a similar quantity of green herbage compared with the LGI swards, and, compared with LGI cows, the HGI cows removed a higher proportion of this green herbage during grazing. Digestibility of the LGI swards was lower because of the higher content of dead herbage but cows in both groups rejected this dead material and selected a diet of similar digestibility. The presence of dead herbage in the LGI swards appeared to reduce animal production by reducing availability and intake of green herbage rather than by reducing the digestibility of the diet selected by the cows. The high grazing intensity increased daily net accumulation of grass leaf in spring (1 7 v. 6 kg/ha of DM, P< 0.05) but reduced that of true stem (-4 v. 28 kg/ha, P < 0.10) and of total herbage (43 v. 54 kg/ha, P<0.10). The HGI swards had higher ryegrass tiller densities in summer and higher (P<0.05) net accumulation rates of herbage in summer through to winter). Increased grazing intensity in spring above normally accepted levels increased pasture utilisation in spring and summer, and milk production in summer, and increased the quantity of spring herbage available for conservation.
Three experiments were conducted to determine the association between leaf number per tiller at defoliation, water-soluble carbohydrate (WSC) concentration and herbage mass of juvenile ryegrass plants when grown in a Mediterranean environment. Seedlings of ryegrass were grown in nursery pots arranged side-byside and located outside in the open-air to simulate a mini-sward in Experiments 1 and 2, and a mixture of annual ryegrass and subterranean clover (Trifolium subterraneum L.) was grown in a small plot field study in Experiment 3. Swards were defoliated mechanically with the onset of defoliation commencing within 28 d of germination. Frequency of defoliation ranged from one to nine leaves per tiller, whilst defoliation height ranged from 30 mm of pseudostem height that removed all leaf laminae in Experiment 1, to 50 mm of pseudostem height with some leaf laminae remaining postdefoliation in Experiments 2 and 3.A positive relationship between herbage mass of ryegrass, WSC concentration and leaf number per tiller at defoliation was demonstrated in all experiments. In Experiment 1, the herbage mass of leaf, pseudostem and roots of tillers defoliated at one leaf per tiller was reduced to 0AE10, 0AE09 and 0AE06 of those tillers defoliated less frequently at six leaves per tiller. However, the reduction in herbage mass from frequent defoliation was less severe in Experiment 2 and coincided with a 0AE20 reduction in WSC concentration of pseudostem compared with 0AE80 measured during Experiment 1. In Experiment 3, the highest harvested herbage mass of ryegrass occurred when defoliation was nine leaves per tiller. Although the harvested herbage from this sward contained senescent herbage, the in vitro dry-matter digestibility of the harvested herbage did not differ significantly compared with the remaining treatments that had been defoliated more frequently.Leaf numbers of newly germinated ryegrass tillers in a Mediterranean environment were positively associated with WSC concentration of pseudostem and herbage mass. A minimum period of two to three leaf appearances was required to restore WSC concentrations to levels measured prior to defoliation thereby avoiding a significant reduction in herbage mass. However, maximum herbage mass of a mixed sward containing ryegrass and subterranean clover was achieved when defoliation was delayed to nine leaves per tiller.
Neutral detergent fibre (NDF), acid detergent fibre (ADF) and water soluble carbohydrate (WSC) levels were determined on 80 samples of known apparent dry matter digestibility (DMD) and voluntary intake of dry matter (DMI). The pastures consisted of regrowths of six species: Trifolium repens (white clover cv. Grasslands Huia), Lolium perenne x L. multiflorum (short rotation ryegrass c.v Grasslands Manawa), Lolium perenne (long rotation ryegrass cv. Grasslands Ariki), Lolium perenne (perennial ryegrass cv. Tasmania No. I), Dactylis glomerata (cocksfoot cv. Currie) and Dactylis glomerata (cocksfoot cv. Grasslands Apanui), cut eight times between May 1969 and August 1970. Overall, white clover had a lower NDF and a lower WSC content than the ryegrasses but both groups had similar ADF contents. Cocksfoots had higher NDF and ADF, and lower WSC contents than the ryegrasses. NDF and ADF could be used to predict the DMD of all species in all seasons with residual standard deviations (RSD) of 3.0 and 3.2 DMD units (per cent) respectively. No significant relations (P < 0.05) were present between DMD and WSC content. Seasonal differences were present in the relations between DMI and chemical composition. The RSD of the overall regressions of intake with NDF, ADF, and WSC contents were 9.3, 9.4, and 8.9 DMI units (g/day/kg0.75) respectively. Within seasons, DMI was best predicted by regressions with detergent fibre content and here the RSD had a range of 3.4 to 5.2 DMI units. Within species over all seasons, DMI was predicted best by regressions with WSC content and the RSD had a range of 5.7 to 7.9 DMI units. The usefulness of the chemical composition measurements in explaining the reason for the low intakes, previously found with winter pasture, is discussed.
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