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Perennial ryegrass (Lolium perenne L.) is often subject to transient waterlogging during winter under dryland conditions and summer when flood-irrigated. Despite this, little is known about the physiological responses of perennial ryegrass genotypes to waterlogging. In a pot experiment, four perennial ryegrass genotypes with contrasting root growth characteristics were subjected to waterlogging for 0, 3, 7, 14, 21 or 28 days. The masses of roots and shoots of the genotype Aurora6 were not significantly (P>0·05) reduced by waterlogging, throughout the experiment. All other genotypes exhibited reductions in root and shoot biomass between 14 and 21 days after waterlogging was imposed. The masses of laminae and roots of susceptible genotypes were reduced by up to 70% after 28 days of waterlogging. Aurora6 was also able to maintain photosynthesis for longer into the waterlogging period. However, after 28 days of waterlogging, photosynthesis of all genotypes was reduced by 30–50%. The waterlogging tolerance of Aurora6 was not due to its relatively poor root growth, as its progeny (2178), which also had poor root growth under control conditions, was susceptible to waterlogging. These findings show that there is variation in physiological processes and herbage yield of perennial ryegrass under waterlogged conditions. The implications of these findings for the genetic improvement of waterlogging tolerance of perennial ryegrass are discussed.

A short-term shading treatment was used to create a Phalaris aquatica L. pasture with alternating strips of ‘low’ [62 mg/g dry matter (DM)] and ‘high’ (126 mg/g DM) water-soluble carbohydrate (WSC) concentration. Analyses showed that starch and all components of the WSC were reduced in concentration by shading. The shaded and unshaded pasture strips did not differ significantly in in vitro DM digestibility (84% DM), nitrogen (3.1% DM), or neutral detergent fibre concentration (42.4% DM). Synthetic alkanes were applied to the pasture strips as markers to measure the selection of the shaded and unshaded pasture by sheep. When 12–13-month-old Merino wethers were given simultaneous access to both pasture treatments, they selected 2.6-fold more unshaded (high WSC) pasture than shaded pasture. The results indicate the involvement of herbage total WSC and its components in the process of diet selection by sheep, and suggest that in future studies, more attention should be paid to reporting data for total WSC concentration.

The concentrations of water-soluble carbohydrate (WSC) and its components, starch, total nitrogen, and dry matter of phalaris (Phalaris aquatica L. cv. Australian) pasture were varied by shading for periods ranging from 38.5 to 46.5 h. In unshaded pasture, WSC concentrations were lowest at sunrise [103 mg/g dry matter (DM)] and increased until early afternoon (to 160 mg/g DM). Sucrose and starch increased in concentration during daylight, whilst the concentrations of glucose, fructose, fructan, and a component of WSC considered to be mainly the carbohydrate moiety of glycoside(s) were relatively constant. The concentrations of starch, and all components of WSC except sucrose, were reduced by shading, but increased to the concentrations observed in the unshaded pasture within 2–4 h after removal of the cover. The fructans present in phalaris were determined to be oligosaccharides of degree of polymerisation (DP) 3 and DP 4 and high molecular mass fructans with DP >10. Nitrogen concentration of shaded pasture was initially higher (4.7% DM) than in unshaded pasture (3.9% DM), but decreased after removal of the shade cover. Dry matter content was reduced in shaded pasture, partly due to increased retention of water on the exterior of plants. The experiment was a precursor for a grazing trial in which the WSC content of pasture was to be altered by shading. It indicated that shading would potentially alter WSC and N concentrations, and DM content, but would have only a relatively small impact on the digestibility of the pasture.

Annual grass pasture (mainly annual ryegrass) was treated at seed head emergence (12 October 1990) with the herbicide glyphosate to delay loss of digestibility during late spring and summer. The lowest rate of glyphosate application needed to retain a high digestibility in the dry matter (DM) of the senescent grass sward was 180 g a.i./ha. The in vitro DM digestibility of control (unsprayed) pasture declined rapidly from relatively high levels near anthesis (28 October) (77n86%, leaves and seed head; 66%, stems) until about 38 days after anthesis (51n71%, leaves and seed head; 24%, stem). Thereafter, the digestibility of the plant parts did not change appre- ciably over at least 4 months. Treatment with glyphosate significantly slowed the loss in digestibility of stem, leaf sheaths, and seed head but did not affect the decline in digestibility of leaf blades. For example, the digestibility of stem in the sprayed pasture was 26 percentage units higher than that in the control pasture 38 days after anthesis. If the time at which digestibility of stems reached 50% is taken as an indication, the effective delay in loss of digestibility was of the order of 5 weeks. However, improved digestibility in the treated pasture was achieved at the expense of pasture yield, with the peak yield of control pasture being 4 t DM/ha (45%) higher than that of the treated pasture. Improved digestibility in treated grass pasture was mainly associated with delayed loss of water-soluble carbohydrates (WSC), except in the seed head. Improved cell wall (neutral detergent fibre) digestibility also con- tributed to varying degrees and was the main factor contributing to improved digestibility in the seed head. The major WSC present in the treated pasture was fructan. The crude protein concentrations of all plant parts of the senescent pasture, except the leaf blades, were also increased by treatment with glyphosate. Additional keywords: annual ryegrass, digestibility, fodder, fructans, herbicide, Lolium rigidum, senescent pasture, soluble carbohydrates.

Previous papers in this series have demonstrated that, when annual pastures were sprayed at seed head emergence with low rates of the herbicide glyphosate, the nutritive value of the sprayed herbage was improved. Housed sheep preferred sprayed herbage to unsprayed herbage and, within sprayed herbage, appeared to have a preference for stem material. The housed sheep ate more of the sprayed material and their weight gains were improved. If such responses occurred in grazing animals, they could result in substantial improvements in animal liveweights or wool production. The present paper describes the alkane-based procedures used to investigate diet selection and herbage intake in grazing animals, with the emphasis placed on methodological and statistical issues. The alkane concentrations in the plant fractions (leaf, leaf sheath, stem, seed head) of sprayed and unsprayed herbage are reported. Similarly, the alkane concentrations in extrusa samples collected by oesophageally fistulated sheep given access to the grazed areas, and in the faeces of sheep grazing the areas, are reported. Patterns of alkane concentrations in extrusa and faeces were similar and indicated that, in the short term, oesophageally fistulated animals consumed a diet of similar composition to that selected by the animals resident on the plots. Using these data for alkane concentrations, multivariate statistical analyses are presented which provide an objective basis for selecting the alkanes to be used in the estimation of diet selection. The results of the first of 4 grazing periods are presented, as an example of the application of the alkane-based procedures for estimating herbage intake and, in particular, diet composition. Use of these techniques indicated that, when given access to sprayed senescent pasture, sheep consumed more digestible dry matter and selected more of it from the stem fraction than was the case with unsprayed herbage. These results are similar to those found with housed animals and demonstrate that patterns of herbage and faecal alkane concentrations can be used to estimate diet composition of grazing animals in terms of the plant parts on offer