Performance of sheep systems grazing perennial pastures. 1. Pasture persistence and enterprise productivity

Sheep production can be optimised by matching the pasture supply curve to feed demand. This study evaluated the production from four management systems with Merino ewes during 2006–2010 in southern New South Wales by using different combinations of lambing time (winter, split, spring), ram breed (Merino, terminal), and percentage of summer-active pasture species (40% or 20% lucerne, Medicago sativa). All systems were stocked at a similar midwinter rate (dry-sheep equivalents per hectare of 8, 10.2, 13, 11.2 and 11.2 in the successive seasons 2006–2010), and there were three replicates of each system. Groundcover and pasture persistence were not adversely impacted by sheep system because sheep were removed at predetermined biomass triggers. Wool production per hectare was up to 178% or 12 kg/ha higher (P < 0.001) in systems where a later month of lambing allowed an increase in number of ewes per hectare at the same midwinter stocking rate. The quantity of lamb sold was not consistently higher in any one system, or in systems producing both crossbred and Merino lambs vs only Merino lambs, owing to variation in the weight and age of lambs at sale, but was increased (P < 0.001) by 175 kg/ha with use of 40% compared with 20% lucerne in a high-rainfall year. The risk of requiring high levels of supplementary feeding was higher in systems with later lambing because of below-average rainfall between 2006 and 2009. Large increases in production can be achieved from the same pasture base through choice of management system with different lambing time, stocking rate or ram breed, but flexibility is needed to optimise production in varying seasonal conditions.

Field evaluation of perennial grasses and herbs in southern Australia. 2. Persistence, root characteristics and summer activity

Field experiments were carried out at seven sites in southern Australia from 2002 to 2006 to measure changes in plant frequency, root characteristics and summer activity for a range of grass and herb species or cultivars. Annual rainfall during the experimental period was on average 75 mm lower than the long-term average. Plant frequency differed significantly between species and between sites. Temperate grasses generally had higher frequencies than subtropical grasses, native grasses and herbs. Cocksfoot (Dactylis glomerata cvv. Currie, Porto), tall wheat grass (Thinopyrum ponticum cv. Dundas), winter-active tall fescue (Festuca arundinacea cvv. Fraydo, Resolute MaxP) and phalaris (Phalaris aquatica cvv. Atlas PG, Australian) were the most persistent of the temperate perennial species over the experimental period. The frequency of most cultivars declined from year 2 to year 4 after establishment, but the frequency of kikuyu (Pennisetum clandestinum cv.Whittet) and wallaby grass (Austrodanthonia richardsonii cv. Taranna) increased by over 5% from year 2 to year 3, and cocksfoot (cv. Currie) increased from year 3 to year 4. At two sites where measurements were made, there were significant differences in rooting depth between species. Whittet kikuyu was the deepest among all species with a rooting depth of up to 2 m, followed by phalaris, tall fescue, grazing brome (Bromus stamineus) and tall wheat grass. Root density was affected by plant genotype and soil structure. Root density of the species varied significantly in the subsoil (0.1–1.1 m) and deeper subsoil (1.1–2 m) but not in the topsoil (0–0.1 m). Green-leafiness over summer was generally higher for subtropical grasses, native grasses, herbs and some summer-active temperate grasses, than most temperate grasses with high summer dormancy.

Sustainable grazing systems for the Central Tablelands of New South Wales. 1. Agronomic implications of vegetation - environment associations within a naturalised temperate perennial grassland

Temperate perennial grass-based pastures dominate the high rainfall zone of south-eastern Australia and support a major livestock production industry. This area has experienced a recent change in overall pasture condition, however, typified by a reduction in the abundance of perennial grasses and an increasingly prominent winter-annual grass weed component. Improving the condition and productivity of these pastures can be achieved by improved management but this requires better knowledge of the interactions between management options and pasture species composition and of the interaction between pasture vegetation and the complex effects of a heterogeneous landscape. This paper reports the results of an intensive survey of a 60-ha paddock that was designed to identify the species present, determine their patterns of distribution and examine the relationships between pasture vegetation and the environment. The survey of species present in late summer was supplemented by the identification of seedlings that later emerged from extracted soil cores and by soil physical and chemical analyses. Data were analysed using ordination and interpreted with GIS software so that topographic features could be considered. The most frequently identified taxa were Hypochaeris radicata, Austrodanthonia spp. and Bothriochloa spp. (in late summer) and Vulpia spp., Bromus molliformis and Trifolium subterraneum (winter-annual species). Austrodanthonia spp. were commonly found on the drier ridges and more acid soils with lower phosphate levels. These were also the areas dominated in spring by Vulpia spp. and were generally lower in plant species richness overall. The most species-rich areas occurred downslope where soil fertility was higher and less moisture stress was presumably experienced. The measured environmental factors explained a substantial proportion of the variation in the vegetation dataset, which underlined the importance of considering landscape effects in the management of typical tablelands pastures.

Root depth of native and sown perennial grass-based pastures, North-West Slopes, New South Wales. 2. Estimates from changes in soil water content

Root depth of pasture is an important hydrological parameter that has substantial implications for the use of rainfall by plants and in estimating deep drainage using biophysical modelling. Studies were undertaken for native and sown perennial grass-based pastures on the North-West Slopes of New South Wales to investigate 4 approaches that may identify the depth of plant roots based on objective assessments of change in soil water content (SWC). The 4 approaches were to examine traces of SWC measured with a neutron moisture meter (NMM) at about 4-week intervals (0–210 cm profile at 20-cm increments) for defined periods with root depth interpreted as, (i) the maximum depth at which there was a distinct decrease in SWC, (ii) the maximum depth at which there was a >0.01 m3/m3 decrease in SWC, (iii) the uppermost depth at which the change in SWC was significant using t0.05, and (iv) the uppermost depth at which the daily rate of change in SWC was significant using t0.05. For each of these approaches, 4 preliminary criteria were applied as filters to the SWC data before they were used in these analyses, (i) the depth of NMM tubes and maximum depth of measurement of SWC was greater than the anticipated pasture root depth, (ii) the depth of initial profile wetting was greater than the anticipated pasture root depth, (iii) there was a drying period of >3 months duration in the major pasture growth phase to allow pastures to extract soil water to the maximum extent, and (iv) the SWC was measured at a sufficient frequency to determine extraction of soil water by roots. SWC data were available from spring 1997 to spring 2001 for Barraba (45 access tubes, native pasture), Manilla (45 tubes, native pasture) and Nundle (36 tubes, sown pasture). Analyses of monthly rainfall compared with mean values identified 3 times where substantial rainfall was followed by an extended drying period. These periods occurred in 1998, 1999 and 2000. SWC data for the 1998 drying period best met all the preliminary filters, particularly criteria (ii) and (iii). Root depth values estimated from these data using the 4 approaches were not significantly different for Barraba (188 ± 4 to 190 ± 3 cm, n = 45), Nundle (142 ± 5 to 143 ± 7 cm, n = 13) and Manilla Red Chromosol (164 ± 7 to 176 ± 7 cm, n = 14), but were significantly different for Manilla Brown Vertosol (98 ± 7 to 121 ± 7 cm, n = 23). It was concluded that reliable estimates of root depth may be readily obtained for a range of soils and environments by firstly applying the 4 simple criteria used in these studies to the SWC data and by determining the depth of significant drying using t0.05. The depth of significant drying approach was the most objective, providing consistent results among sites and accounting for variance among NMM counts and tubes in these studies.

Changes in soil water content under annual- and perennial-based pasture systems in the wheatbelt of southern New South Wales

Nine pasture treatments differing in species composition were monitored for changes in soil water content at a depth of 0.10–1.70 m, at 2 sites (Kamarah and Junee), in the wheatbelt of eastern Australia. Treatments containing perennial species, viz. lucerne (Medicago sativa L.), phalaris (Phalaris aquatica L.), cocksfoot (Dactylis glomerata L.), mixture (lucerne + phalaris + cocksfoot), wallaby grass (Austrodanthonia richardsonii Cashmore.), and lovegrass (Eragrostis curvula (Schrader) Nees.), were sown with subterranean clover (Trifolium subterraneum L.). In addition, 3 treatments based solely on annual species were examined: subterranean clover (sown by itself and kept weed-free with herbicides), annual (sown to subterranean clover but weed invasion not controlled), and serradella (Ornithopus compressus L.). The experiment was conducted from 1994–97 at the Junee site (annual average rainfall 550 mm/year) and from 1995–97 at the Kamarah site (annual average rainfall 450 mm per year). At the higher rainfall site (Junee), there were few differences among pasture types in soil water content to 0.70 m. Below 0.70 m the soil profile was drier under all the perennial swards than under the annual pasture treatments by the end of the 4-year pasture phase. At the drier Kamarah site, where the pasture phase was shorter due to an initial sowing failure, all the perennials, except cocksfoot, dried the profile below 1.05 m. At both sites, lucerne dried the 1.05–1.70 m section of the soil profile more rapidly than the other perennials, which apparently took longer to reach this depth. At the Junee site, the soil water deficit in May (SWD(MAY), defined as field capacity (mm) – stored soil water (mm) at the beginning of May) was largest in the phalaris, mixture, lucerne, and cocksfoot treatments (155–162 mm), whereas as under a pasture of subterranean clover alone, SWD(MAY) was only 89 mm. At the drier Kamarah site, the largest SWD(MAY) was created by the lovegrass (114 mm) and lucerne (107 mm) treatments. The cocksfoot and subterranean clover treatments created the smallest SWD(MAY) at this site, at 79 and 72 mm, respectively. The study showed that currently available C3 and C4 perennial grasses can be as effective as lucerne in drying the soil profile to 1.70 m in the 450–600 mm rainfall areas of the southern NSW wheatbelt, creating a dry soil buffer to reduce the risk of deep drainage during subsequent cropping phases. As the rate at which grasses dried the profile was slower than lucerne, pastures based on perennial grasses may have to be retained longer to achieve the same level of dewatering.

Sustainable grazing systems for the Central Tablelands of New South Wales. 5. A bioeconomic framework for assessing the long-term economic benefits of grazing management tactics and implications for sustainability

There have been significant declines in the perennial grass (PG) content in native and sown pastures across temperate Australia. Not only has this reduced agricultural productivity, it has contributed to more serious degradation, such as loss of soil and biodiversity, decreasing water quality, and dryland salinity caused by rising watertables. Results from the Sustainable Grazing Systems Key Program (SGS) research undertaken at Carcoar on the Central Tablelands of New South Wales were reported by Michalk et al. (2003). This research indicated that grazing management tactics can be used to manipulate pasture composition, thereby changing animal production and water-use patterns. The main grazing tactic investigated was termed a summer grazing rest, where resting was imposed in late spring if PG composition was <50%. Reported in this present paper is an economic framework for valuing the long-term benefits of grazing management tactics. The framework involves the development of a bioeconomic modelling system that links a dynamic programming model with biophysical models for water and environmental processes, soil fertility, pasture growth, livestock energy requirements and the change in pasture species composition. The study concludes that long-term economic returns are improved by strategies, e.g. a summer rest, that lead to an increase in PG composition over time. The study also determined that environmental factors, such as deep drainage, runoff and soil loss, are reduced as perenniality is increased.

Sustainable grazing systems for the Central Tablelands of New South Wales. 4. Soil water dynamics and runoff events for differently-managed pasture types

Soil water, runoff amount and quality, pasture production and environmental data were measured for a pastoral prime lamb enterprise in the Central Tablelands of New South Wales from 1998 to 2002. There were 4 pasture treatments: fertilised and sown chicory (CH), fertilised and sown introduced pastures (SP), fertilised naturalised pastures (FN) and unfertilised naturalised pastures (UN). Two grazing management regimes, tactically grazed (TG) and continuously grazed (CG) were imposed on the SP, FN and UN treatments. The CH treatment was rotationally grazed. To compare pasture and grazing system water use, maximum soil water deficit values (SWDMax) were calculated from neutron moisture meter data. SWDMax was influenced by both environmental and management factors. Management factors that influenced SWDMax were herbage mass of perennials, degree of perenniality, and the perennial species present. Environmental factors accounted for >50% of the variation in SWDMax. Inclusion of management factors (perennial herbage mass of C3 and C4 species and percentage perennial herbage mass), accounted for an additional 16% of variation. While the influence of pasture management appears to be relatively small, importantly, management is the only avenue available to land managers for influencing SWDMax. The UNTG and all sown treatments, with greater perennial herbage mass or greater C4 herbage mass consistently produced the highest SWDMax. Runoff amount and quality data are presented for ground cover percentages which generally exceeded 80% for the experimental period. Runoff as a proportion of rain received during the experiment was <3%. Environmental factors explained 47% of variation in runoff, while pasture herbage mass and ground cover percentage explained an additional 2% of variation. Water quality was monitored on 3 treatments (SPTG, FNTG and UNCG) for total nitrogen (N), total phosphorus (P) and total suspended solids (TST) over a 6-month period. The mean values for total N and P were below the acceptable contaminant concentration for agricultural irrigation water. An important outcome of this research is the concept of a practical Targeted Water Management Plan (TWMP) which devises a framework for optimum water usage and productivity at a landscape scale.

Pasture and sheep responses to lime application in a grazing experiment in a high-rainfall area, south-eastern Australia. II. Liveweight gain and wool production

‘Managing Acid Soils Through Efficient Rotations (MASTER)’ is a long-term pasture–crop rotation experiment commenced in 1992. One of the objectives was to demonstrate the extent of crop, pasture, and animal responses to lime application on a typical acidic soil in the 500–800 mm rainfall zone of south-eastern Australia. Two types of pastures (perennial v. annual pastures) with or without lime application were established in 1992. Fifteen- to eighteen-month-old Merino hoggets were used as test animals and were changed annually. This paper reports the results of sheep responses to liming from the 4 continuous pasture treatments over 6 years from 1992 to 1997. The stocking rate was the same on all plots within a treatment during each rotation period, but was varied between treatments based on the pasture availability and sheep body condition. The most important findings from this study are that the limed treatments carried 29% and 27% more stock (up to 4 DSE/ha) than the unlimed treatments for perennial and annual pastures, respectively. As a result, the limed perennial pastures produced 27% more liveweight gain (62 kg/ha.year) and 28% more greasy wool (13 kg/ha.year) than unlimed perennial pastures, whereas the limed annual pastures produced 34% more liveweight gain (77 kg/ha.year) and 24% more greasy wool (11 kg/ha.year) than unlimed annual pastures. The significant responses to lime in liveweight and wool production were detected from the second growing season after the pastures were established. The increased sheep productivity on the limed treatment was due to a combination of increased pasture production and improved pasture quality. Perennial pastures showed a slight advantage in wool production, but not in liveweight gain. However, the seasonal variation of liveweight was greater on annual pastures than on perennial pastures. The larger variation in liveweight change could lead to more adverse effects on wool quality especially at high grazing pressures. Grazing management can be used to manipulate pasture and animal productivity to increase profits from lime use.

Eragrostis curvula (Schrad.) Nees. complex pastures in southern New South Wales, Australia: a comparison with Medicago sativa L. and Phalaris aquatica L. pastures under rotational grazing

A grazing experiment conducted in Wagga Wagga (New South Wales) from September 1993 to September 1998 compared the productivity of pastures containing 3 palatable types of summer-active Eragrostis curvula complex, with pastures containing either Medicago sativa or Phalaris aquatica. Issues relating to the management of E. curvula pastures were also investigated. Herbage growth rates of the P. aquatica and M. sativa pastures were highest in winter and spring; E. curvula pastures were most productive in summer and autumn. Stocking rates equivalent to 30–40 dry sheep were carried by the pastures during their growing seasons. Throughout the study, the pastures were dominated by their respective sown perennial species, however, a suite of desirable and undesirable annual grasses and annual legumes usually contributed >20% of total herbage mass in spring. The P. aquatica pasture contained a higher proportion of weedy species than the other pastures, especially C4 grasses and broadleafed species, and towards the end of the experiment it was also invaded by several native perennial grasses. Overall, the wool yield from the M. sativa pasture was 0.5–1.0 kg/animal.year higher than the other pastures. Management to minimise herbage accumulation on the E. curvula pastures was a key issue, and provided that pastures were grazed heavily, this was achieved by the rotational grazing strategy used in the experiment. It was concluded that palatable varieties of E. curvula have a useful and complementary role as perennial pastures in southern Australia. By increasing herbage availability in summer and autumn, E. curvula may improve management flexibility for a wide range of pastures that are commonly grown on farms.