DairyMod, EcoMod, and the SGS Pasture Model are mechanistic biophysical models developed to explore scenarios in grazing systems. The aim of this manuscript was to test the ability of the models to simulate net herbage accumulation rates of ryegrass-based pastures across a range of environments and pasture management systems in Australia and New Zealand. Measured monthly net herbage accumulation rate and accumulated yield data were collated from ten grazing system experiments at eight sites ranging from cool temperate to subtropical environments. The local climate, soil, pasture species, and management (N fertiliser, irrigation, and grazing or cutting pattern) were described in the model for each site, and net herbage accumulation rates modelled. The model adequately simulated the monthly net herbage accumulation rates across the range of environments, based on the summary statistics and observed patterns of seasonal growth, particularly when the variability in measured herbage accumulation rates was taken into account. Agreement between modelled and observed growth rates was more accurate and precise in temperate than in subtropical environments, and in winter and summer than in autumn and spring. Similarly, agreement between predicted and observed accumulated yields was more accurate than monthly net herbage accumulation. Different temperature parameters were used to describe the growth of perennial ryegrass cultivars and annual ryegrass; these differences were in line with observed growth patterns and breeding objectives. Results are discussed in the context of the difficulties in measuring pasture growth rates and model limitations.

Abstract. The dry matter (DM) yield, plant persistence and forage quality of tall fescue (Festuca arundinacea) and perennial ryegrass (Lolium perenne) were compared in the subtropical environment of southern Queensland, Australia. The field study was conducted under irrigation with pure, nitrogen fertilised stands of 10 commercial tall fescue cultivars (Advance, AU Triumph, Bombina, Cajun, Dovey, Maximise, Midwin, Torpedo, Quantum and Vulcan), 3 experimental cultivars (ITF 97010, ITF 97020 and PWF 29) and Dobson perennial ryegrass. From July 1997, plots were defoliated at 4-week intervals for 3 years. Changes in crude protein content and in vitro DM digestibility (IVDMD) were determined at 1, 2, 3, 4, 6 and 8 weeks post-defoliation in October (spring) 1997, January (summer), March (autumn), June (winter) and September (spring) 1998.Some cultivars of irrigated tall fescue were shown to be better adapted to a subtropical environment than perennial ryegrass. After 3 years, cumulative DM yields were in excess of 30 t/ha for Dovey, Quantum, ITF 97010, AU Triumph and Cajun tall fescue compared with 12 t/ha from Dobson perennial ryegrass swards.Plant development had a considerable influence on crude protein content and IVDMD of tall fescue and perennial ryegrass, more so than the length of the regrowth period. As plant tissue matured, the forage quality during spring declined linearly for crude protein content and for IVDMD (1998 only), and declined exponentially for IVDMD during spring (1997), summer, autumn and winter (1998). Quality losses may be minimised if tall fescue cultivars are defoliated every 2-3 weeks during spring and summer and every 3-4 weeks during autumn and winter.

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.

A high proportion of the Australian and New Zealand dairy industry is based on a relatively simple, low input and low cost pasture feedbase. These factors enable this type of production system to remain internationally competitive. However, a key limitation of pasture-based dairy systems is periodic imbalances between herd intake requirements and pasture DM production, caused by strong seasonality and high inter-annual variation in feed supply. This disparity can be moderated to a certain degree through the strategic management of the herd through altering calving dates and stocking rates, and the feedbase by conserving excess forage and irrigating to flatten seasonal forage availability. Australasian dairy systems are experiencing emerging market and environmental challenges, which includes increased competition for land and water resources, decreasing terms of trade, a changing and variable climate, an increasing environmental focus that requires improved nutrient and water-use efficiency and lower greenhouse gas emissions. The integration of complementary forages has long been viewed as a means to manipulate the home-grown feed supply, to improve the nutritive value and DM intake of the diet, and to increase the efficiency of inputs utilised. Only recently has integrating complementary forages at the whole-farm system level received the significant attention and investment required to examine their potential benefit. Recent whole-of-farm research undertaken in both Australia and New Zealand has highlighted the importance of understanding the challenges of the current feedbase and the level of complementarity between forage types required to improve profit, manage risk and/or alleviate/mitigate against adverse outcomes. This paper reviews the most recent systems-level research into complementary forages, discusses approaches to modelling their integration at the whole-farm level and highlights the potential of complementary forages to address the major challenges currently facing pasture-based dairy systems.

The effect of defoliation on the vegetative, early reproductive and inflorescence stages of tiller development, changes in the dry‐matter yield of leaf, stem and inflorescence and the associated changes in forage quality was determined on plants of annual ryegrass (Lolium rigidum Gaud.) and Italian ryegrass (L. multiflorum Lam.). The field study comprised seventy‐two plots of 1 m × 2 m, sown with one annual ryegrass and seven Italian ryegrass cultivars with a range of heading dates from early to late; defoliation commenced 6 weeks after germination. During the vegetative stage of growth, plots were defoliated when the tillers had three fully expanded leaves (three‐leaf stage). During the early reproductive stage of growth, to simulate a cut for silage, plots were defoliated 6–7 weeks after 0·10 of the tillers displayed nodal development. The subsequent regrowth was defoliated every 3 weeks. Assessments of changes in tiller density, yield and quality were made in the growth cycle that followed three contrasting cutting treatments during the winter–spring period (from 10 July). In treatment 1, this growth cycle (following closing‐up before a subsequent conservation cut) commenced on 7 August following two defoliations each taken when the tillers were at the three‐leaf stage. In treatment 2, the growth cycle commenced on 16 October following: for early‐maturing cultivars, two cuts at the three‐leaf stage, a cut for silage and an additional regrowth cut; for medium‐maturing cultivars three cuts at the three‐leaf stage and a cut for silage; and late‐maturing cultivars, five cuts at the three‐leaf stage. In treatment 3, defoliation up to 16 October was as for treatment 2, but the growth cycle studied started on 27 November following two additional regrowth cuts for early‐ and medium‐maturing cultivars and cut for silage for the late‐maturing cultivars. Tiller development for all cultivars was classified into three stages; vegetative, early reproductive and inflorescence. In treatment 1, in vitro dry‐matter digestibility (IVDMD) and crude protein (CP) content were negatively associated with maturation of tillers. IVDMD ranged from 0·85 to 0·60 and CP ranged from 200 to less than 100 g kg–1 dry matter (DM) during the vegetative and inflorescence stages respectively. This large reduction in forage quality was due to an increase in the proportion of stem, inflorescence and dead material, combined with a reduction in the IVDMD and CP content of the stem. A high level of forage quality was retained for longer with later‐maturing cultivars, and/or when vegetative tillers were initiated from the defoliation of early reproductive tillers (treatments 2 and 3). However, 15 weeks after the closing‐up date in treatment 1, defoliation significantly reduced the density of inflorescences with means (±pooled s.e_m.) of 1560, 1178 and 299 ± 108 tillers m–2, and DM yield of inflorescence with means of 3·0, 0·6 and 0·1 ± 0·15 t ha–1 for treatments 1, 2 and 3 respectively. This study supports the recommendation that annual and Italian ryeg...