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Context The use of dual-purpose crops (for grazing and grain) has increased in the high-rainfall zone in southern Australia. Aim A systems experiment examined the impact on livestock production and supplementary feeding when dual-purpose crops were incorporated into a production system based on Merino ewes producing yearling lambs for sale. Methods The experimental site near Canberra, ACT, was subdivided into nine experimental units (‘farmlets’) with three replicate farmlets for each of three production-system treatments. Each farmlet was managed as a self-contained unit with six Merino ewes and their progeny during 2013–16 (4 years). Ewes were joined in February, lambed in July and shorn in spring; the original cohort of ewes (born 2009) was replaced by a new cohort (born 2012) at the midpoint of the experiment. Six weaners were retained after weaning in each farmlet and sold as yearlings. Control farmlets were sown to pasture based on phalaris (Phalaris aquatica L.) and subterranean clover (Trifolium subterraneum L.) and comprised sub-paddocks to allow rotational grazing. Farmlets in treatments that included dual-purpose crops comprised six sub-paddocks (0.231 ha), with two sown to permanent pasture, and four supporting a rotation of pasture–pasture–dual-purpose canola (Brassica napus L.)–dual-purpose wheat (Triticum aestivum L.). In one of the crop–pasture production system treatments, crop-grazing was prioritised for ewes (ECG treatment); in the other, crop-grazing was prioritised for their progeny weaners (WCG treatment). Key results Greasy fleece weight from ECG (5.3 kg) and WCG (5.1 kg) ewes was higher (P < 0.001) than from control ewes (4.7 kg) averaged over the 4 years. The final sale weight of yearling weaners from the WCG system (44.3 kg) was higher (P < 0.001) than from the control (39.2 kg) or ECG (39.1 kg) systems when averaged over the 4 years. The benefit was predominantly due to greater weight gain during the period when weaners grazed the crop during late autumn and winter. Sale weight of lamb per hectare was higher (P = 0.003) in the WCG treatment (216 kg) compared with the ECG treatment (186 kg) when averaged over the 4 years of the experiment but did not differ (P > 0.05) to the control (201 kg). Meat production over the 4 years was higher (P < 0.001) in the WCG system (226 kg/ha) than other treatments when weight gain from wethers in 2014 was included. The impact of including dual-purpose crops on supplementary feeding was variable and depended on seasonal conditions. Conclusions Incorporation of dual-purpose crops into the high-rainfall production system can increase meat and wool production, with the highest meat production being obtained when crop grazing was prioritised for young carry-over livestock. Implications Prioritising dual-purpose crops for young growing livestock can increase meat production from the system while allowing other livestock classes (wethers or ewes) to graze the crops in better seasons when there was excess forage that would otherwise have been under-utilised.

Context Growing of dual-purpose crops for grazing by livestock has increased in popularity in the high-rainfall zone of southern Australia, a livestock production zone traditionally based on permanent perennial grass species. Aims A systems experiment examined the impact on pasture forage availability, sheep grazing days and crop yields when one-third of a farmlet was sown to dual-purpose wheat (Triticum aestivum L.) and canola (Brassica napus L.) crops. Methods The experiment comprised nine experimental units (farmlets) divided into three treatments with three replicate farmlets per treatment: control farmlets sown to phalaris (Phalaris aquatica L.)-based pastures; and two treatments with grazing of crops prioritised for either ewes or their progeny. Control farmlets comprised four sub-paddocks (0.231 ha each) in 2013 and six sub-paddocks in 2014–2016. Farmlets in treatments that included dual-purpose crops comprised six sub-paddocks (0.231 ha), with two sub-paddocks sown to permanent pasture and the other four sub-paddocks supporting a pasture–pasture–canola–wheat rotation. Key results Crops were sown in February or early March and grazing commenced by mid-May in all years. Canola was grazed first in the sequence in 3 of 4 years. Treatments had similar total sheep grazing days per year, except for the progeny-prioritised treatment in 2014 when agistment wethers were introduced to utilise excess crop forage. Grazing did not affect wheat yields (3.9 vs 3.7 t/ha, P > 0.05) but did reduce canola yields (3.6 vs 3.0 t/ha, P = 0.007). Pasture availability (dry matter per ha in the pasture paddock at entry by sheep) was higher in the control during late summer and autumn when the crops were being established; however, resting of pastures during late autumn and winter while crops were grazed resulted in no difference in pasture availability among treatments during spring. Conclusion and implications The key feed-gap is in late summer and autumn when dual-purpose crops are included in the system. Early and timely sowing of crops increases the grazing opportunity from dual-purpose crops before lock-up. Growing wheat plus canola provided some hedge against poor establishment and/or slow growth rates in one of the crops.

An improved ability to predict pasture dry matter (DM) yield response to applied phosphorus (P), potassium (K) and sulfur (S) is a crucial step in determining the production and economic benefits of fertiliser inputs and the environmental benefits associated with efficient nutrient use. The adoption and application of soil testing can make substantial improvements to nutrient use efficiency, but soil test interpretation needs to be based on the best available and most relevant experimental data. This paper reports on the development of improved national and regionally specific soil test–pasture yield response functions and critical soil test P, K and S values for near-maximum growth of improved pastures across Australia. A comprehensive dataset of pasture yield responses to fertiliser applications was collated from field experiments conducted in all improved pasture regions of Australia. The Better Fertiliser Decisions for Pastures (BFDP) database contains data from 3032 experiment sites, 21918 yield response measures and 5548 experiment site years. These data were converted to standard measurement units and compiled within a specifically designed relational database, where the data could be explored and interpreted. Key data included soil and site descriptions, pasture type, fertiliser type and rate, nutrient application rate, DM yield measures and soil test results (i.e. Olsen P, Colwell P, P buffering, Colwell K, Skene K, exchangeable K, CPC S, KCl S). These data were analysed, and quantitative non-linear mixed effects models based upon the Mitscherlich function were developed. Where appropriate, disparate datasets were integrated to derive the most appropriate response relationships for different soil texture and P buffering index classes, as well as interpretation at the regional, state, and national scale. Overall, the fitted models provided a good fit to the large body of data, using readily interpretable coefficients, but were at times limited by patchiness of meta-data and uneven representation of different soil types and regions. The models provided improved predictions of relative pasture yield response to soil nutrient status and can be scaled to absolute yield using a specified maximal yield by the user. Importantly, the response function exhibits diminishing returns, enabling marginal economic analysis and determination of optimum fertiliser application rate to a specific situation. These derived relationships form the basis of national standards for soil test interpretation and fertiliser recommendations for Australian pastures and grazing industries, and are incorporated within the major Australian fertiliser company decision support systems. However, the utility of the national database is limited without a contemporary web-based interface, like that developed for the Better Fertiliser Decisions for Cropping (BFDC) national database. An integrated approach between the BFDP and the BFDC would facilitate the interrogation of the database by advisors and farmers to generate yield response curves relevant to the region and/or pasture system of interest and provides the capacity to accommodate new data in the future.

In recent decades several pasture legumes have been available in southern Australia as potential alternatives to the most widely used annual pasture legume Trifolium subterraneum. Little is known about their soil phosphorus (P) requirements, but controlled environment experiments indicate that at least some may differ in their P fertiliser requirements. In this study, pasture legume varieties, including T. subterraneum as the reference species, were grown at up to four sites in any one year over a 3-year period (in total, seven site × year experiments) to measure herbage growth responses in spring to increased soil P availability. A critical soil test P concentration (corresponding to 95% maximum yield) was estimated for 15 legumes and two pasture grasses. The critical soil P requirements of most of the legumes did not differ consistently from that of T. subterraneum, indicating their soil fertility management should follow the current soil test P guidelines for temperate Australian pastures. However, the critical P requirement of Medicago sativa was higher than that of T. subterraneum, but remains ill-defined because extractable soil P concentrations in these experiments were often not high enough to permit a critical P estimate. Three forage crop legumes (Trifolium incarnatum, Trifolium purpureum, Trifolium vesiculosum) and two pasture legumes (Ornithopus compressus, Ornithopus sativus) had lower critical soil test P concentrations. It may be feasible to manage pastures based on these species to a lower soil test P benchmark without compromising yield.

Trifolium subterraneum L. is widely grown in the phosphorus (P) deficient soils of southern Australia. However, this pasture legume has a high critical external P requirement and requires frequent applications of P fertiliser to achieve high productivity. Twenty-six genotypes of T. subterraneum were grown to determine: (i) differences in shoot growth and P acquisition under low-P supply; (ii) the root morphological traits important for P acquisition; and (iii) the feasibility of selection among genotypes for these root morphological traits. Micro-swards of each genotype were grown with a topsoil layer that was either moderately P-deficient or had P supplied in excess of the critical requirement for maximum yield; the subsoil layer was P-deficient. Yield and P content of shoots and roots were determined after 5 weeks’ growth, and root samples were assessed for diameter, length and root hair length. All genotypes were equally highly productive when excess P was supplied. However, relative shoot yield in the moderately P-deficient soil ranged from 38–71%. Total root length ranged from 63–129 m pot–1, and was correlated with total plant P uptake (R2 = 0.78, P < 0.001). Variation was also observed in average root diameter (0.29–0.36 mm) and root hair length (0.19–0.33 mm). These traits were combined with root length to calculate the total surface area of the root hair cylinder, which was also correlated with total plant P uptake (R2 = 0.69, P < 0.001). The results demonstrated that there was significant variation in P acquisition efficiency and shoot yield among genotypes of T. subterraneum when grown in P-deficient soil, and that root length was important for improved P uptake. The results indicate potential to identify superior genotypes that achieve improved P acquisition and higher shoot yields in low-P soil.

The mainstream pasture legume species such as Trifolium subterraneum, T. repens and annual Medicago spp. used in the temperate pasture systems of southern Australia have high critical external requirements for phosphorus (P) (i.e. P required to achieve 90% of maximum yield). This work aimed to identify alternative pasture legume species that could be used in systems with lower P input. Shoot and root biomass of 12 species of pasture legume was measured in response to seven rates of P applied to the top 48 mm of soil in a pot experiment. Most species had maximum yields similar to T. subterraneum, but some required only one-third of the applied P to achieve this. The critical external P requirement of the species, ranked from lowest to highest, was as follows: Ornithopus compressus = O. sativus

Root traits related to phosphorus (P) acquisition are used to make inferences about a species’ P-foraging ability under glasshouse conditions. However, the effect on such root traits of constrained canopy spread, as occurs in dense pasture swards, is unknown. We grew micro-swards of Trifolium subterraneum L. and Ornithopus compressus L. at 15 and 60 mg kg–1 soil P in a glasshouse. Shoots either spread beyond the pot perimeter or were constrained by a cylindrical sleeve adjusted to canopy height. After 8 weeks, shoot and root dry mass (DM), shoot tissue P concentration, rhizosphere carboxylates, arbuscular mycorrhizal (AM) fungal colonisation, total and specific root length (TRL and SRL respectively), average root diameter (ARD) and average root hair length (ARHL) were measured. In all species and treatments, constrained canopy spread decreased root DM (39–59%), TRL (27–45%) and shoot DM (10–28%), and increased SRL (20–33%), but did not affect ARD, ARHL and AM fungal colonisation. However, shoot P concentration and content increased, and rhizosphere carboxylates increased 3.5 to 12-fold per unit RL and 2.0- to 6.5-fold per micro-sward. Greater amounts of rhizosphere carboxylates when canopy spread was constrained appeared to compensate for reduced root growth enabling shoot P content to be maintained.

Annual pasture legume species can vary more than 3-fold in their critical external phosphorus (P) requirement (i.e. P required for 90% of maximum yield). In this work we investigated the link between root morphology, P acquisition and critical external P requirement among pasture species. The root morphology acclimation of five annual pasture legumes and one grass species to low soil P availability was assessed in a controlled-environment study. The critical external P requirement of the species was low (Dactylis glomerata L., Ornithopus compressus L., Ornithopus sativus Brot.), intermediate (Biserrula pelecinus L., Trifolium hirtum All.) or high (Trifolium subterraneum L.). Root hair cylinder volumes (a function of root length, root hair length and average root diameter) were estimated in order to assess soil exploration and its impact on P uptake. Most species increased soil exploration in response to rates of P supply near or below their critical external P requirement. The legumes differed in how they achieved their maximum root hair cylinder volume. The main variables were high root length density, long root hairs and/or high specific root length. However, total P uptake per unit surface area of the root hair cylinder was similar for all species at rates of P supply below critical P. Species that maximised soil exploration by root morphology acclimation were able to prolong access to P in moderately P-deficient soil. However, among the species studied, it was those with an intrinsic capacity for a high root-hair-cylinder surface area (i.e. long roots and long root hairs) that achieved the lowest critical P requirement.

Rytidosperma species are perennial grasses found in cool temperate grasslands of Australia. The species differ in their intrinsic growth rates, response to phosphorus (P) fertiliser application and critical external P requirements (P required for 90% maximum growth). The present study examined whether internal P-utilisation efficiency (PUE) by Rytidosperma species influenced these differences. The PUE of nine Rytidosperma species and two grasses of Mediterranean origin, Bromus hordeaceus L. and Lolium perenne L., was assessed using alternative measures of shoot P concentration or its reciprocal. No measure of PUE was correlated with the critical external P requirements of the species. One measure of PUE, shoot dry matter per unit P, when assessed at a common shoot P content was correlated with potential growth rate (P

Persistence is consistently claimed by Australian farmers as a high priority for perennial grasses in long-term pastures. Phalaris (Phalaris aquatica L.) is a productive perennial grass with proven persistence in south-eastern Australia. Nevertheless, factors that determine the persistence of pasture species in southern Australia related to climate (drought), soil (acidity), grazing pressure, and, importantly, their interaction can reduce persistence of phalaris and other species in various situations. These factors and their interactions are discussed in this review, and strategies to improve persistence with emphasis on plant breeding approaches are considered, with the most durable outcomes achieved when breeding and management options are employed concurrently. Two examples of breeding to improve persistence traits in phalaris are described. A program to improve acid-soil tolerance resulted first in the release of cv. Landmaster, and recently Advanced AT, which is the most aluminium (Al)-tolerant cultivar of phalaris to date. It was bred by recurrent selection on acid soils in a population containing genes from a related, more Al-tolerant species, P. arundinacea. The higher Al tolerance of cv. Advanced AT is of most benefit in more assured establishment on acid soils under variable moisture conditions and confers improved flexibility of sowing date. Cultivar Holdfast GT was bred to address complaints of poor persistence under heavy grazing by cultivars of the highly productive, winter-active type, since high grazing tolerance is needed to achieve profitable returns from developed pastureland. Evidence of good persistence under grazing for cv. Holdfast GT and possible tradeoffs with productivity are discussed. Maintaining high productivity under a predicted higher incidence of drought stress (climate change) and increasing areas of acid soils presents ongoing challenges for persistence in pastures.

Phosphorus (P) fertilisers are important for productivity in many grassland systems. Phosphorus is a non-renewable and finite resource, and there are environmental and economic reasons for using P more effectively. We review the P balance of temperate pastures to identify the factors contributing to inefficient use of P fertiliser and discuss ways to improve P-balance efficiency. Immediate gains can be made by ensuring that P fertiliser inputs are managed to ensure that the plant-available P concentrations of soil do not exceed the minimum concentration associated with maximum pasture production. Unnecessarily high soil P concentrations are associated with greater potential for P loss to the wider environment, and with higher rates of P accumulation in soils that have a high P-sorption capacity. Soil microorganisms already play a crucial role in P cycling and its availability for pasture growth, but are not amenable to management. Consequently, plants with lower critical P requirements, particularly because of better root foraging, will be an important avenue for improving the P-balance efficiency of fertilised pastures. Traits such as long fine roots, branching, root hairs, and mycorrhizal associations all contribute to improved root foraging by pasture plants; some of these traits are amenable to breeding. However, progress in breeding for improved P efficiency in pasture plants has been minimal. It is likely that traditional plant breeding, augmented by marker-assisted selection and interspecific hybridisation, will be necessary for progress. There are practical limits to the gains that can be made by root foraging alone; therefore, plants that can ‘mine’ sparingly available P in soils by producing organic anions and phosphatases are also needed, as are innovations in fertiliser technology.

Phosphorus (P) fertilisers are one of the key tools available for increasing pasture production and the profitability of grazing enterprises. However, recent rapid changes in fertiliser price have increased the importance of developing optimal management strategies for applying P fertiliser and setting stocking rates. We applied a novel combination of process-based grazing systems modelling and randomised cash flow analyses to examine how changes in fertiliser price affect optimal fertiliser application rates and stocking rates for sheep grazing systems in south-eastern Australia, simultaneously taking into account long-term economic viability and environmental sustainability. We used ‘GrassGro’, a grazing systems decision support tool, to simulate three sheep enterprise types (Merino wethers, Merino ewes, crossbred ewes) at two locations (Hamilton, Victoria; Bookham, New South Wales). Gross margins from each year simulated in GrassGro (1966–2007) were randomised 500 times and input to a cash flow analysis that identified the financially optimal stocking rate for a range of fertiliser applications and the financial risk frontiers (combinations of stocking rate and fertiliser input for which the enterprise becomes financially unviable). For all enterprises examined at both locations, the optimal combinations of stocking rate and fertiliser application rate did not vary markedly as fertiliser price changed. Regardless of enterprise type or location, the fertiliser application rate at which the highest gross margins were achieved provided the greatest range of stocking rates that were both financially viable and environmentally sustainable. Increases in fertiliser price reduced the combinations of stocking rate and fertiliser application rate that were viable in the long term, emphasising the importance of well informed grazing management decisions.

Phosphorus (P) is an important nutrient required for plant growth and its management in soil is critical to ensure sustainable and profitable agriculture that has minimal impact on the environment. Although soils may contain a large amount of total P, only a small proportion is immediately available to plants. Australian soils often have low availability of P for plant growth and P-based fertilisers are, therefore, commonly used to correct P deficiency and to maintain productivity. For many soils, the sustained use of P fertiliser has resulted in an accumulation of total P, a proportion of which is in forms that are poorly available to most plants. The efficiency with which different P fertilisers are used in agricultural systems depends on their capacity to supply P in a soluble form that is available for plant uptake (i.e. as orthophosphate anions). In addition to fertiliser source, the availability of P in soil is influenced to a large extent by physico-chemical and biological properties of the soil. Plant access to soil P is further affected by root characteristics (e.g. rate of growth, specific root length, and density and length of root hairs) and biochemical processes that occur at the soil–root interface. The ability of roots to effectively explore soil, the release of exudates (e.g. organic anions and phosphatases) from roots that influence soil P availability, and the association of roots with soil microorganisms such as mycorrhizal fungi are particularly important. These processes occur as a natural response of plants to P deficiency and, through better understanding, may provide opportunities for improving plant access to soil and fertiliser P in conventional and organic agricultural systems.

The difference between cation and anion concentrations is an important property when assessing feed for dry dairy cows in order to avoid hypocalcaemia following calving. Dietary cation–anion difference (DCAD) is used to assess suitability of feed and predict the risk of milk fever; a value of –5 cmol(+)/kg dry matter (DM) or less is desirable. This work has examined the DCAD of 16 field-grown species found in pasture in southern Australia. The DCAD [cmol(+)/kg DM] at the flowering stage varied from 7 to 32 for grasses, 21 to 72 for legumes and 72 to 99 for dicot weeds. The average DCAD for legumes was 50 cmol(+)/kg DM, over 2-fold higher than the 20 cmol(+)/kg DM average for grasses. There was a substantial decline in DCAD of herbage as the season progressed. In a glasshouse experiment with five grass species in an acid soil, lime application increased yield and tended to lower the DCAD. Lime decreased uptake per unit root length of potassium and chlorine and increased uptake of calcium by phalaris and timothy. While DCAD is an important attribute of herbage for assessing its suitability for prepartum diets of dairy cows, the present data indicate that it would be prudent to also consider concentrations of calcium and other mineral nutrients in herbage, particularly when examining less familiar plant species or the effects of different cultural practices on the composition of herbage for such diets.

The accumulation and phosphatase-lability of organic P was investigated in soil taken from 3 pastures that had received contrasting fertiliser management over 8 years. The soils were either unfertilised or had received superphosphate either from 1994 to 1997 or applied annually to 2002. P-fertilisation led to an increase in both the inorganic and organic P content of the soils, but with differences in the distribution of organic P in various extractable pools. Fertilisation also affected the amount of organic P that was amenable to hydrolysis by a non-specific phosphatase. In particular, the amount of water-extractable organic P that was phosphatase-labile was greatest in soil that had received continuous fertiliser application. Despite improved phosphatase-lability of different organic P pools in the fertilised soils, transgenic Trifolium subterraneum L., which releases extracellular phytase, showed no consistent advantage in growth and P nutrition compared with either wild-type or azygous controls when grown in intact cores of soil. This indicates that organic P that accumulates with P-fertilisation is either not an effective substrate for transgenic plants that exude phytase or is equally available to transgenic and control plants.

Grassland production in southern Australia is generally based on phosphorus (P)- and nitrogen (N)-deficient soils. Use of P-fertiliser is necessary for high production in higher rainfall zones and economic pressures are increasing the need to apply fertiliser more widely and consistently. The P and N requirements of 10 temperate pasture species were examined to understand how increased fertiliser use will affect grassland botanical composition. The plant species fell into 2 main groups with respect to their critical external P requirements (P application rates required to achieve 90% of maximum yield) : those with a high requirement (Trifolium subterraneum, Hordeum leporinum, Bromus molliformis, Microlaena stipoides, and Phalaris aquatica), and those with a low requirement (Lolium rigidum, Vulpia spp., Austrodanthonia richardsonii, and Holcus lanatus). The critical external N requirements of H. leporinum, L. rigidum, and B. molliformis were significantly higher than those of A. richardsonii, Arctotheca calendula, and H. lanatus. Species that ‘tolerate’ nutrient stress were relatively abundant in unfertilised grazing systems and tall ‘competitor’ species were dominant in fertilised pasture under low grazing pressure. The abundance of the species present in fertilised pastures grazed for high utilisation was negatively correlated with their relative growth rates and it is hypothesised that this may indicate that abundance was determined by tolerance or avoidance of grazing.

Botanical composition (basal cover) was measured in 4 replicated pasture treatments based on Phalaris aquatica and Trifolium subterraneum at Hall, ACT (unfertilised with low and high stocking rate; fertilised with low and high stocking rate) and in 2 unreplicated pasture treatments based on native perennial grasses (Austrodanthonia spp. and Microlaena stipoides) and T. subterraneum at Bookham, NSW (unfertilised and low stocking rate; fertilised and high stocking rate). Current economic pressures are encouraging graziers to increase their use of phosphorus (P) fertiliser and to adopt higher stocking rates. The objective of the research was to determine the changes in botanical composition that may result from these changes in grazing systems management. At Hall, annual species differed in their responses to P fertility. Notably, basal cover of Bromus spp. increased significantly with P application, whereas Vulpia spp. decreased significantly. Basal cover of T. subterraneum also increased significantly with P application when stocking rate was high, but was reduced by P application if stocking rate was low. Basal cover of perennial grasses (P. aquatica and Holcus lanatus) was significantly higher at low stocking rate when P was applied. The botanical composition of high stocking rate treatments was relatively stable over time, which contrasted with less stable composition at low stocking rate. At Bookham, fertilised pasture in unreplicated paddocks appeared to have a higher basal cover of productive annual species (i.e. Bromus spp. and T. subterraneum), but native perennial grasses appeared to have lower basal cover in comparison with the unfertilised area. These results indicated that in some cases, the influence of P fertiliser and high stocking rates on botanical composition was favourable (i.e. increased basal cover of P. aquatica and T. subterraneum) and in others it could be detrimental (i.e. lower basal cover of native perennial grasses).

The effects of site and season on the nutritive value of 16 perennial ryegrass cultivars and 60 half-sib families were assessed at 2 locations in South West Victoria. Crude protein, water-soluble carbohydrates, neutral detergent fibre and in vitro digestibility were measured on vegetative herbage, harvested in either autumn or spring. While no heritable genetic variation for nutritive value parameters was detected in this set of families, consistent differences in the nutritive value of cultivars were measured across sites and seasons. The cultivars Yatsyn1 and Ellett were consistently high in both water-soluble carbohydrates and in vitro digestibility. The differences in mean nutritive value between high and low ranking cultivars were ~40 g/kg water-soluble carbohydrates and 3–5% in vitro digestibility. These consistent differences in forage quality demonstrate the value of measuring forage quality during cultivar evaluation. The identification of cultivars with improved nutritive value will also facilitate the crossing of the alleles that confer this improvement into other genetic backgrounds.

A field study was carried out in the high rainfall zone (HRZ, >600 mm p.a.) of southern Australia from March 1994 to August 1997 to test the hypothesis that sown perennial grasses and liming could make the existing pastures more sustainable through better use of water and nitrogen. The site, on an acid duplex soil at Book Book near Wagga Wagga in southern New South Wales, was typical of much of the HRZ grazing country in southern New South Wales and north-east Victoria. The experiment consisted of 4 replicate paddocks (each 0.135 ha) of 4 treatments: annual pasture (mainly ryegrass Lolium rigidum, silver grass Vulpia spp., subterranean clover Trifolium subterraneum and broadleaf weeds) without lime, annual pasture with lime, perennial pasture (phalaris Phalaris aquatica, cocksfoot Dactylis glomerata and subterranean clover T. subterraneum) without lime, and perennial pasture with lime. Soil pH (0–10 cm) in the limed treatments was maintained at 5.5 (0.01 mol/L CaCl2), compared to 4.1 in the unlimed treatments. The pastures were rotationally grazed with Merino ewe or wether hoggets at a stocking rate which varied with the season, but was 10–25% higher on the limed pastures [14.8–17.3 dry sheep equivalent (dse)/ha] than the unlimed pastures. One replicate set of pasture treatments was intensively monitored for surface runoff, subsurface flow (at the top of the B horizon), water potential gradients and ammonium volatilisation. Other measurements of nitrogen inputs, transformations and losses were made on all paddocks. In a normal to wet year, surface runoff, subsurface flow and deep drainage (>180 cm depth) were about 40 mm less from the perennial than the annual pastures. The reduction in deep drainage under the perennials was about one-third to one-half (20–29 mm/year). The smaller loss of solution NO3– from the perennial pastures (up to 12 kg N/ha.year) suggested soil acidification under perennials was reduced by about 1 kmol H+/ha.year. Denitrification and volatilisation losses of N were small (1–12 kg N/ha.year). Nitrogen fixed by subterranean clover (above ground parts) ranged from 2–8 kg N/ha in the drought of 1994–95 to 128 kg N/ha in a normal year (1996). The soil-pasture nitrogen balance was positive for all treatments and averaged 76 kg N/ha.year over 2 years. The abundance of introduced and native earthworms increased from 85 to 250/m2 in the limed pastures between 1994 and 1997. Introduced species, such as Aporrectodea trapezoides, were especially responsive to lime. Animal production per hectare was 10–25% higher on pastures with lime. Critical gross margins per dse were lowest ($16/ha) for a long-lived perennial pasture (>15 years), and highest ($20/ha) for a short-lived perennial (5 years). Overall, there were substantial benefits in animal production, improved soil quality and water use from establishing perennial grass pastures with lime on these strongly acid soils.

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.

The treatment of annual ryegrass–silver grass pasture with the herbicide glyphosate at seed head emergence delayed the loss of soluble carbohydrates and improved herbage digestibility. The present study investigated whether this improvement in nutritive value had any influence on the diet preference, intake, and performance of housed sheep. Since the effects of glyphosate on digestibility were most marked in stem tissue, preference was examined not only in relation to sprayed v. unsprayed herbage, but also in terms of preference for individual plant parts. In the preference testing, sheep showed a marked preference for sprayed rather than unsprayed herbage. They also consumed more of it, such that their digestible dry matter intake from sprayed herbage was nearly twice that from unsprayed herbage. When sheep were offered different plant fractions from the control herbage, they selected against stem material and preferred leaf or seed head. By contrast, when offered fractions from the sprayed material, they preferred stem to leaf, but showed no strong preference for stem over seed head. Preference was related more to the soluble carbohydrate content of a plant part than its digestibility, and only when soluble carbohydrate contents were similar was there preference for the more digestible material. The consumption of sprayed herbage, compared with control herbage, led to higher concentrations of rumen volatile fatty acids in the period 4 h after feeding. Moreover, the feeding of these herbages over a 6-week period resulted in significant reductions in pre-feeding plasma urea and β-hydroxybutyrate concentrations. When control herbage was fed with supplements of fructose, urea, or fructose+urea, in an attempt to mimic the possible differences in nutritive value between control and sprayed herbage, the responses in rumen and blood metabolites were less marked than when sprayed herbage was fed. As a consequence of the higher nutritive value of the sprayed herbage and the higher intakes by the animals fed this material, sheep fed sprayed herbage were able to maintain weight over the feeding period, whereas those offered the control herbage lost weight at 130–150 g/day

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

Phytase and acid phosphatase activities were measured in extracts from roots of 14- to 22- day old seedlings of a range of temperate pasture species that were grown aseptically in sand culture. Phytase activity from roots of phosphorus- (P-)-deficient Trifolium subterraneum L. was characterised. Activity was enhanced by 40% when extracts were passed through Sephadex G-25, and increased by a further 20–30% with the addition of either 1 mМ EDTA or 5 mМ cysteine to assay solutions. The optimum temperature for phytase activity was 50°C and the optimum pH was 5.3. When compared with phosphatase activity measured in the roots of T. subterraneum, phytase activity exhibited narrower pH and temperature optima, and was also more strongly inhibited by Co2+, Zn2+ and AsO42− ions. Significantly, for the five pasture species examined, phytase activity was less than 5% of the total acid phosphatase activity in extracts of plant roots. Measured phytase activity ranged between 0.13 and 1.7 nkat g–1 root fresh wt and was enhanced under P-deficient relative to P-sufficient growth conditions in all of the pasture species with the exception of Trifolium repens L., for which the Km constant for activity was 50% lower in P-deficient plants. When expressed on a root fresh wt basis, increases in phytase activity of ~1.25-fold were observed for extracts from T. subterraneum and Medicago polymorpha L., and of up to 3.3-fold for Danthonia richardsonii A.B. Cashmore and Phalaris aquatica L. Increases in acid phosphatase activity with P deficiency were less evident. Between 3.1% and 4.3% only of the total phytase activity measured in root extracts was eluted from intact roots into 0.1 М NaCl.

Nitrogen uptake and nitrate (NO-3) leaching below 1.1 m was estimated under phalaris, cocksfoot, and annual ryegrass pastures and under bare fallow in a 4-year field experiment under control and high N (500 kg N/ha) treatments in north-eastern Victoria (693 mm/year rainfall for the study period). The perennial grasses, particularly phalaris, took up more N in herbage than annual ryegrass. High concentrations of NO3-N were measured at 1 m depth below all treatments, suggesting that NO3- losses from pastures have potential to contaminate streams and/or groundwater. Perennial pastures were only able to reduce NO3- leaching compared with annuals in drier than average years. Values calculated for acid addition due to NO3-leaching resulted in a net annual input of approximately 1 kmol H +/ha.year under the phalaris pasture compared with 2 kmol H +/ha.year under annual ryegrass. Adding these figures to carbon cycle addition data of 1 kmol H+/ha.year (measured in a previous study) corresponds to a lime rate of 100 and 150 kg lime/ha.year being required to stop further acidification under these pasture types. A 1 unit pH decline to 30 cm depth was estimated to take 42 years under annual pasture or 67 years under perennial grasses. Whilst perennial pastures have a role in reducing soil acidification, lime application is the most important management option in balancing soil acidification caused by agriculture.

We report the effects of spray-topping annual grass pasture with glyphosate (180 g a.i./ha as Roundup CT, at the seed head emergence stage) on the nutritive value of herbage and on subsequent performance of grazing sheep. Eight 1-ha plots, consisting of 4 sprayed and 4 unsprayed (control) plots, were set-stocked with Merino wethers (18 months old, 12 sheep/ha) from 8 days after anthesis in the control plots (late spring) until 165 days after anthesis (mid-autumn). In 4 periods (15–20, 36–41, 71–76, and 99–104 days after anthesis; Periods 1–4, respectively) sheep were dosed with synthetic alkanes and herbage and faecal samples were taken, in order to estimate diet composition (in terms of plant parts), faecal output, herbage intake, and the digestibility of the whole diet. As described in our earlier papers, spray-topping reduced the yield of pasture dry matter, but also slowed the loss of water-soluble carbohydrate (WSC) and digestibility during pasture senescence. The present paper shows that as a result, sheep grazing sprayed herbage in Periods 1 and 2 consumed significantly more organic matter (OM) and digestible OM (DOM) than sheep grazing the control pasture. Their diet contained a higher proportion of stem with a higher WSC concentration than that of the sheep grazing the control plots. The proportions of different plant parts (leaf blade+sheath, stem, seed head) in the diet of both the plot sheep and oesophageally fistulated (OF) sheep, which grazed treatments for short periods, differed significantly between treatments in all periods. However, the compositions of the diets selected by plot and OF sheep were similar. These results confirmed diet preferences measured using housed sheep and demonstrate the usefulness of alkane-based procedures for quantifying diet composition and intake in grazing animals. As a result of their higher intake of DOM, sheep grazing sprayed herbage had a significantly higher liveweight gain over the first 2 periods (40 g/day). In Period 3, sheep grazing sprayed herbage consumed more OM than sheep grazing control herbage. However, DOM intakes from sprayed or control plots were not significantly different in either Period 3 or Period 4, and were lower than in Periods 1 and 2. Sheep grazing both treatments lost liveweight at a similar rate over this time. Wool growth in sheep grazing sprayed herbage was improved by 10% during the experimental period; wool strength was also improved significantly. The implications for the management of sheep grazing spray-topped pastures over summer are discussed.

Summary. Two lines of perennial ryegrass (Lolium perenne L.), cv. Aurora and breeding line Ba 11351, from the United Kingdom with elevated concentrations of water-soluble carbohydrates in the shoot were compared with the standard cultivars, Ellett, Vedette and Kangaroo Valley, in pure grass swards under irrigation at Kyabram, Victoria, and Gatton, Queensland, and under natural rainfall at Condah, Victoria, during 1995–97. Near infrared reflectance spectroscopy was used to predict the water-soluble carbohydrate, crude protein, in vitro dry matter digestibility, neutral and acid detergent fibre, and Klason lignin concentrations of the perennial ryegrass herbage. Herbage yield and water-soluble carbohydrate differed between cultivars at each site at most harvests, with the high water-soluble carbohydrate lines usually yielding less and having higher water-soluble carbohydrate concentrations than the 3 standard cultivars. However, the high water-soluble carbohydrate lines also had higher water-soluble carbohydrate concentrations at harvests where their yield was equal to the standard cultivars. The other nutritive value traits differed significantly at more than half of the 32 harvests: the high water-soluble carbohydrate lines had higher crude protein and dry matter digestibility, and lower neutral detergent fibre, the neutral detergent fibre containing less acid detergent fibre and lignin than did the standard cultivars. The high water-soluble carbohydrate lines were more susceptible to crown rust during spring and summer than the standard cultivars at Kyabram and Gatton: heavy infections reduced yield, water-soluble carbohydrate, dry matter digestibility and crude protein. Higher water-soluble carbohydrate may depend on only a few genes, as does rust resistance and it seems likely that high yielding, high water-soluble carbohydrate cultivars can be developed by recombination and selection.

Summary. The suitability of near infrared reflectance (NIR) spectroscopy for predicting the concentration of several quality traits in samples of annual ryegrass (Lolium rigidum Gaud.) herbage was assessed in 2 separate experiments. In the first experiment, NIR calibration equations were developed for 6 traits (water-soluble carbohydrates, dry matter digestibility, neutral detergent solubles, neutral detergent solubles digestibility, neutral detergent fibre digestibility and nitrogen) using 4 calibration methods. No significant differences were found in the accuracy of NIR equations developed using either stepwise multiple linear regression (SMLR) or partial least squares regression (PLS) techniques when the equations were used to predict the concentration of constituents in those samples not used during the calibration process. The process of removing samples identified by the computer as spectral outliers was found to improve those statistics that related NIR data to the reference data of the samples used during calibration development (i.e. improved the goodness of fit of the regressions). However, when the resulting equations were used on all of the samples there was no improvement in the accuracy of the prediction of composition, and the estimates were less accurate for 2 of the equations. In the second experiment, plant part-specific equations (leaf blade, stem and leaf sheath) were developed. The specific equations were found to be no more accurate than those developed using a subset of all samples when used to analyse samples of the same plant part. However, using equations developed on either stem or leaf sheath samples to predict the composition of leaf blade samples led to inaccurate estimates of composition, illustrating the potential for error when NIR calibration equations are used on dissimilar samples. The similarity of the NIR estimates of decline in nutritive value and those obtained using reference analyses was illustrated by plotting the actual and predicted decline in nutritive value. The results of the experiments in this paper illustrate the need to monitor the accuracy of any NIR prediction of nutritive value. Striving for very low standard errors of calibration either by eliminating outliers or by limiting the plant tissues used during calibration did not lead to more accurate predictions of the composition of samples other than those used during the calibration process.

The water balance equation was used to calculate plant water use and drainage below a depth of 1·1 m for phalaris, cocksfoot, and annual ryegrass pastures and bare fallow at Rutherglen in north-eastern Victoria. Rainfall from 1990 to 1993 averaged 693 mm/year. Soil water use was greater under perennials over the summer{autumn period and the soil profile was approximately 50 mm drier at the beginning of each drainage season. Following autumn rains, soil water profiles under all treatments converged, usually reaching similar water contents within 4{6 weeks. Over 4 years, soil under phalaris became 33 mm drier, and cocksfoot 24 mm drier (P < 0· 001), than under annual ryegrass or bare fallow. Phalaris had higher actual evapotranspiration (P < 0·05; average, 642 mm/year) than cocksfoot (619 mm/year) and annual ryegrass (606 mm/year), the latter two not differing significantly. Drainage occurred during winter and early spring, ranging from 2 to 12 mm in 1991 (515 mm rainfall) to >100 mm/year in 1990 and 1992 (671 mm and 901 mm rainfall, respectively). The variation between years was greater than the differences between pastures in any one year. Averaged over the 4 years, drainage losses below 1 .1 m decreased in the order bare fallow > annual ryegrass > cocksfoot > phalaris, although differences between the 3 pasture types were not statistically significant. Drainage under phalaris and cocksfoot may have been overestimated relative to annual ryegrass and fallow because of subsurface flow, at the top of the B horizon, between the wetter and drier plots. The drainage under phalaris may also have been overestimated because this pasture extracted water below the depth of soil water measurement. Allowing for these effects, the estimated drainage under phalaris may have been 49-56 mm/year compared with 80-87 mm/year under annual ryegrass, an overall reduction of more than one-third. Although perennial pasture grasses are unlikely to stop all recharge to groundwater in high rainfall areas (>600 mm/year) of south-eastern Australia, they offer a practical way to combine profitable agriculture with reduced land degradation.

Differences in the water-soluble carbohydrate concentrations of herbage of northern European perennial ryegrass cultivars (Aurora, Melle, Cariad) grown under southern Australian conditions, and a New Zealand perennial ryegrass cultivar (Ellett) which yields well in southern Australia, were investigated in relation to their nutritive value. The water-soluble carbohydrates (WSC), total nitrogen, in vitro dry matter digestibility (IVDMD), neutral detergent fibre (NDF), and digestibility of NDF (NDFD) were measured in all cultivars. Aurora and Cariad exhibited higher WSC concentrations than the other cultivars, particularly during summer. This buffered the decline in IVDMD that was due to declining NDFD at that time of the year and resulted in an improvement in IVDMD of between 2 and 6%. Although WSC and nitrogen concentrations of the herbage were negatively correlated, this was due mainly to divergent seasonal variation in these components of the herbage.

The effect of time of spraying glyphosate on a sward of annual ryegrass (Lolium ridigum Gaudin) was examined. Glyphosate (180 g a.i. ha-1) was applied at weekly intervals between 21 days prior to anthesis and 14 days after anthesis. The resulting physiological and chemical changes were monitored to assess the contribution of plant components to digestibility during senesence. When applied before anthesis, glyphosate delayed the loss in digestibility of senescing annual ryegrass. However, glyphosate applied at, or after anthesis did not alter the decline in digestibility of the grass compared to the control (unsprayed) treatment. Glyphosate applied before anthesis significantly reduced the development of the grass ear, and delayed the loss of materials soluble in neutral detergent (NDS) from the stem for up to 35 days after anthesis. In control plants, soluble carbohydrates comprised up to 90% of the NDS in the stems, 66% in leaf sheaths, and 25% in leaf blades but were lost almost entirely during senescence. Glyphosate applications before anthesis delayed the loss of soluble carbohydrates until 35 days after anthesis. However, soluble carbohydrate loss occurred after this period and by 66 days there was little difference between control and treated plants. The IVDMD of the neutral detergent fibre (NDF) declined in all parts of the unsprayed grass during senescence. When plants were sprayed with glyphosate, the digestibility of the NDF was maintained or declined only slowly after spraying. Application of glyphosate prior to anthesis resulted in higher stem and sheath nitrogen concentrations. By contrast, glyphosate had little effect on leaf nitrogen concentration. Conservation of feeding value in senescing grass pasture was achieved only by application of glyphosate before anthesis. However, some losses of soluble carbohydrates, and thus digestibility, could not be avoided.

Changes in the digestibility and chemical composition of a L. rigidum cv. Wimmera sward sown in May, 1985 were measured from 21 d pre-anthesis (9 Oct.) until 69 d after anthesis (7 Jan.) when the plants were dead. Max. yield of 11.7 t DM/ha was reached 8 d pre-anthesis. The in vitro DM digestibility (IVDMD) of whole plants decreased from 58% at anthesis to 36% 69 d after anthesis. This was associated with a decrease in the IVDMD of stem, leaf blades and sheaths. In the 3rd stem internode, which was considered representative of the stem, the loss of digestible yield was due to loss of DM soluble in neutral detergent (NDS). The NDS consisted mainly of non-structural carbohydrates. Similar losses of NDS contributed to loss of digestibility in the uppermost leaf blade and leaf sheath. The digestibility of NDS was generally 80-95% but in the leaf blade this declined to 45% as NDS was mobilized during leaf senescence. NDF digestibility of the stem declined from 35% at anthesis to 19% when dead; corresponding values for the uppermost leaf blade were 83 and 54%, resp., and for the leaf sheath 46 and 37%, resp. These characteristics of a senescing grass sward are discussed in relation to options for improving digestibility of dead grass pastures.

The formation of nitrogen-fixing nodules on roots of leguminous plants by Rhizobium spp. involves a complex interaction between host plant and symbiont. Successful nodulation requires the coordinated expression of several nodulation (nod) genes in the bacteria. The expression of these genes is induced by flavonoid compounds present in root exudates of host plants. Growth of Rhizobium spp. and formation of nodules on roots of leguminous plants is known to be adversely affected by low pH and factors associated with soil acidity, but the basis of this acid-sensitivity is poorly understood. We consider that poor induction of nodulation gene expression in Rhizobium is a major factor contributing to the acid-sensitivity of nodulation formation. At low pH, induction of nod gene expression in R. leguminosarum biovar trifolii is markedly reduced in the presence of flavone-inducer. Furthermore, inducibility of nod gene expression in R. leguminosarum bv. trifolii is also affected by a net reduction in the concentration of nod gene-inducing factors present in the root exudates of clover seedlings grown in acidic conditions.