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Approximately 3.1 Mha (22%) of the agricultural area of south-eastern Australia can be classified as native pasture. There is the assumption that, owing to the widespread occurrence of low-fertility soils in Australia, native grass species do not respond to increased phosphorus (P) fertility. Currently, there are no industry recommendations of target soil-test P values for native-grass-based pastures. This paper reviews the responses of perennial native pasture species endemic to south-eastern Australia to P application in controlled environments, surveys, replicated experiments and paired-paddock trials. Eighty-seven site-years of trial data where different levels of P were applied, conducted over the last two decades, on native-based pastures in south-eastern Australia are reviewed. Data indicate that application of P fertilisers to native grass pastures can increase dry matter (DM) production and maintain pasture stability. However, minimum targets for herbage mass (800 kg DM/ha) and groundcover (80%) are required to ensure persistence of perennial native grasses. Stocking rates also need to match carrying capacity of the pasture. Based on previous research, we recommend target soil-test (Olsen; 0–10 cm) P levels for fertility-tolerant native grass pastures, based on Microlaena stipoides, Rytidosperma caespitosum, R. fulvum, R. richardsonii, R. duttonianum and R. racemosum, of 10–13 mg/kg, whereas for pastures based on fertility-intolerant species such as Themeda triandra, lower levels of

At Hamilton, Victoria, the effects of grazing pressure and amount of single superphosphate (SSP) applied, on the productivity and soil resource status of grazing systems based on sheep, have been assessed since 1979. Early work showed that marginal and absolute responses in DM production to SSP were greater when assessed by measuring the net growth of grazed pastures compared with mowing, and that largest response occurred in spring. The botanical composition of the pasture has been dramatically influenced by the amount of SSP applied. Ryegrass and subterranean clover now constitute only 2.3% and 11.0% where an average of 1-4 kg P/ha has been applied each year. In addition, the digestibility of herbage from wellfertilised treatments was 4-9 units higher than from low-fertility treatments. The combination of these effects has allowed achievable annual gross margins to increase from $100/ha at low-fertility treatments to about $400/ha with 18 kg P/ha applied annually. Indicators of sustainability show that so far there have been no major environmental consequences of applying SSP in amounts well above that used by district farmers. Keywords: botanical composition, gross margin, pasture quality, phosphorus, sheep, sustainability

Temperate pastures that leak water below the root zone have been linked to an increase in dryland salinity in southern Australia through their conservative use of stored water. An experiment was conducted at Hamilton in south-western Victoria to test the hypothesis that deep-rooted, summer-active perennial pasture species can substantially reduce leakage. On topographic crests the experiment compared lucerne and chicory with a traditional perennial ryegrass variety with low summer activity, whereas on the poorly drained valleys the comparison was between tall fescue, kikuyu and a perennial ryegrass variety with high summer activity. Lucerne developed a buffer of dry soil to a depth of at least 5 m. An empirical relationship with June–September rainfall indicated that with this dry buffer, leakage below the root zone would not occur even in the wettest of years. Chicory developed a dry buffer to the depth of measurement (3 m), but plant density gradually declined and leakage started to occur 5 years after sowing. The perennial ryegrass with low summer activity had leakage nearly every year. On the valleys kikuyu was initially the most effective at drying the soil in summer, but its density declined at the expense of annuals and 3 years after sowing it became wetter than the other treatments. None of the pasture options on the valley fully controlled leakage, but both the summer-active perennial ryegrass and tall fescue were persistent and there was little difference in their capacity to extract summer moisture. This study showed that four characteristics were associated with a pasture that controlled leakage – summer activity, persistence, adequate density and deep rootedness. Of the species tested only lucerne satisfied all these criteria.

Improved dryland pastures for sheep and beef cattle production in south-western Victoria are typically based on summer-dormant cultivars of perennial ryegrass (Lolium perenne L.) or phalaris (Phalaris aquatica L.). These are highly productive in spring but exhibit low accumulation rates over summer–autumn. Summer-active perennial pasture species could potentially alleviate this summer–autumn feed gap. Three pasture systems that used different pastures on each of the three landscape classes (crest, slope, and valley floor) were compared over 4 years. The perennial ryegrass system (henceforth Ryegrass) had a different ryegrass cultivar on each landscape class. The Triple system used lucerne (Medicago sativa L.) (crest), perennial ryegrass (slope), and summer-active tall fescue (Lolium arundinaceum (Schreb) Darbysh.) (valley floor). The Novel system used chicory (Cichorium intybus L.) (crest), Italian ryegrass (Lolium multiflorum Lam.) or hybrid ryegrass (L. × boucheanum Kunth.) (slope), and kikuyu (Pennisetum clandestinum Hochst. ex Chiov.) (valley floor). The pastures were grazed by either one (in the case of the Novel system) or three (in the case of the Ryegrass and Triple systems) animal systems that varied over the life of the experiment. Total annual herbage accumulation of the Ryegrass and Triple systems did not differ. The Novel system consistently had lower total annual dry matter accumulation than the other two systems. Lucerne pastures generally had the highest accumulation rates over summer, followed by the chicory pastures. The kikuyu pastures responded well to summer rainfall but otherwise had similar accumulation rates to the perennial ryegrass and tall fescue pastures over summer. Tall fescue pastures grew well in autumn following wet summers. In spring the perennial ryegrass pastures based on Fitzroy or Avalon were highly productive but seldom grew faster than other pastures. The results support the hypothesis that incorporating deep-rooted, summer-active perennial species will increase pasture production over summer–autumn compared with conventional pasture systems but not at the expense of winter–spring production.

Climate change projections for Australia predict increasing temperatures, changes to rainfall patterns, and elevated atmospheric carbon dioxide (CO2) concentrations. The aims of this study were to predict plant production responses to elevated CO2 concentrations using the SGS Pasture Model and DairyMod, and then to quantify the effects of climate change scenarios for 2030 and 2070 on predicted pasture growth, species composition, and soil moisture conditions of 5 existing pasture systems in climates ranging from cool temperate to subtropical, relative to a historical baseline. Three future climate scenarios were created for each site by adjusting historical climate data according to temperature and rainfall change projections for 2030, 2070 mid-and 2070 high-emission scenarios, using output from the CSIRO Mark 3 global climate model. In the absence of other climate changes, mean annual pasture production at an elevated CO2 concentration of 550 ppm was predicted to be 24-29% higher than at 380 ppm CO2 in temperate (C-3) species-dominant pastures in southern Australia, with lower mean responses in a mixed C-3/C-4 pasture at Barraba in northern New South Wales (17%) and in a C-4 pasture at Mutdapilly in south-eastern Queensland (9%). In the future climate scenarios at the Barraba and Mutdapilly sites in subtropical and subhumid climates, respectively, where climate projections indicated warming of up to 4.4 degrees C, with little change in annual rainfall, modelling predicted increased pasture production and a shift towards C-4 species dominance. In Mediterranean, temperate, and cool temperate climates, climate change projections indicated warming of up to 3.3 degrees C, with annual rainfall reduced by up to 28%. Under future climate scenarios at Wagga Wagga, NSW, and Ellinbank, Victoria, our study predicted increased winter and early spring pasture growth rates, but this was counteracted by a predicted shorter spring growing season, with annual pasture production higher than the baseline under the 2030 climate scenario, but reduced by up to 19% under the 2070 high scenario. In a cool temperate environment at Elliott, Tasmania, annual production was higher than the baseline in all 3 future climate scenarios, but highest in the 2070 mid scenario. At the Wagga Wagga, Ellinbank, and Elliott sites the effect of rainfall declines on pasture production was moderated by a predicted reduction in drainage below the root zone and, at Ellinbank, the use of deeper rooted plant systems was shown to be an effective adaptation to mitigate some of the effect of lower rainfall.

To assess the risks and benefits of more intensive pasture management, 2 or 3 treatments with contrasting fertiliser regimes were selected from each site of the Sustainable Grazing Systems national experiment. The assessment used soil coring data, modelling and runoff nutrient concentration data.Soil acidification rates were estimated from the simulated nitrate leaching and product removal estimated from the stocking rates at each site. Much higher acidification rates were estimated at sites in Victoria and southern Western Australia than in northern New South Wales. This was because of a lower level of nitrate leaching in summer-dominant rainfall environments coupled with lower stocking rates. Simulations showed highest nitrate leaching on annual pastures, but that a phalaris pasture could reduce this, and a kikuyu pasture could almost fully control leaching.The concentration of P in surface runoff was related to soil P status at the 4 southern sites, indicating that greater use of P fertiliser would increase P movement into waterways. There was no relationship between soil P status and P in surface runoff at the northern New South Wales sites, and across all sites there were no relationships between P fertility and runoff N levels. Concentrations of P and N in runoff greatly exceeded stream water quality guidelines, even on treatments where only minimal P had been applied as fertiliser. There was also evidence of high spatial variation in surface runoff generation, with surface runoff from some plots less than 5% of the streamflow in nearby reference streams. There is therefore scope to control P concentrations in streams by retiring from production the parts of the landscape that generate high quantities of surface flow, but to intensify production on areas that produce little runoff.

The effects of combinations of different fertiliser rates and grazing methods applied to phalaris-based pastures on an acid, saline, yellow sodosol on the Dundas Tablelands of western Victoria (mean annual rainfall 623�mm) were measured from 1997 to 2000. The objective was to help identify management systems that improve phalaris growth and persistence, water use, and animal production, and thereby the productivity and sustainability of grazing systems. Pastures were either set stocked with low [mean 6.4 kg phosphorus (P)/ha.year] or high (mean 25 kg P/ha.year) fertiliser rates, or rotationally grazed with high fertiliser (mean 25 kg P/ha.year). Rotational grazing was implemented as either a simple '4-paddock' system (fixed rotation length), or a more intensive system where rotation length varied with pasture growth rate. Unreplicated paddocks of volunteer pasture (dominated by onion grass and annual grass weeds) receiving an average of 8 kg P/ha.year were also monitored. All treatments were stocked with spring-lambing Merino ewes. Stocking rate was an emergent property of each treatment, and was driven by pasture quality and availability. Total pasture herbage accumulation ranged from 7150 to 9750 kg DM/ha.year and was significantly lower on the set-stocked, low-fertility treatment than on all other treatments. A significant treatment.day effect in the spline analysis of herbage mass was explained by a trend toward higher pasture mass in the rotationally grazed treatments than set-stocked treatments from the break of season until mid-spring. Rotational grazing led to significantly higher phalaris herbage accumulation than set stocking (mean 3680 v. 2120 kg DM/ha.year), but significantly lower subterranean clover herbage accumulation (1440 v. 2490 kg DM/ha.year). Despite the stronger growth of deep-rooted phalaris in the rotationally grazed treatments, maximum soil water deficits at the end of summer differed only slightly between treatments, with the difference between driest and wettest treatments amounting to only 14 mm. Summer growth of phalaris was apparently insufficient to generate significant differences in soil water extraction at depth, even when phalaris content was increased by rotational grazing, and re-wetting of the soil profile occurred at a similar rate for all treatments. Rotationally grazed treatments supported higher stocking rates than set-stocked treatments at high fertiliser rates (mean 14.9 v. 13.7 ewes/ha), but apparent losses in pasture feeding value due to lower legume content under rotational grazing meant that there were few significant differences between treatments in lamb production per hectare. The experiment showed that grazing method can have a substantial and rapid effect on pasture botanical composition. There are clear opportunities for producers to use temporal and spatial combinations of set stocking and rotational grazing to manipulate herbage mass and pasture composition within broad target ranges for achieving both animal production (e.g. high per-head animal performance) and sustainability (e.g. persistence of perennial grasses) objectives. Rigid application of either set stocking or rotational grazing imposes limitations on both pasture and animal production, and neither grazing method will optimise system performance under all conditions. The experiment also demonstrated that management and land-use changes that have much greater potential to increase water use than those examined here will be needed to ensure the sustainability of pasture systems in the high rainfall zone of western Victoria.

Relationships between amounts of superphosphate applied to pasture and stocking rate on available nutrient status were assessed from 1979 to 2000 on a chromosol derived from basalt at Hamilton, Victoria. The pastures were stocked with sheep at low, medium, or high grazing pressures in factorial combination with 6 levels of superphosphate. Overall annual amounts of single superphosphate (8.8% P, 11% S, 19% Ca) applied ranged from 0.4 to 36 kg P/ha. Potassium chloride (KCl) was applied to all plots periodically. Average stocking rates ranged from 7 to 19 dry sheep equivalents (DSE)/ha. The nutrient status of plots was monitored by sampling the soil to a depth of 10 cm, avoiding the areas used by the sheep for camping. In 1994, samples of topsoil (0–5 cm and 5–10 cm) were taken from the camp areas and non-camp areas in each plot in order to assess 'plant-available' P, S, and extractable cations. Changes in P and S with depth to 80 cm in high and low grazing pressure treatments were also assessed. The influence of cumulative P applied on Olsen P varied with time and grazing pressure. During the first 12–15 years, the Olsen P of high grazing pressure plots was greater than that of low grazing pressure plots, but subsequently the reverse has been the case. Plant-available S also increased where more superphosphate had been applied. Levels were greater than 7 mg S/kg soil except at the lowest level of superphosphate, indicating that forms of P fertiliser with less S could be used here. After initial applications of KCl, this fertiliser was not applied for 8 years. During this time the K status fell from 270 to 120 mg K/kg soil, just above where plant responses to K are likely, emphasising the need to monitor the K status of productive pastures on these soils. Levels of exchangeable Mg2+ fell as more superphosphate was used, whereas levels of Ca2+ rose. The Olsen P of soil deeper than 10 cm was always less than 5 mg P/kg soil. P supply to deep-rooted pasture plants may thus be limiting when the topsoil is dry. These results, together with published assessments of animal production at this site, show that for pastures fertilised annually, the Olsen P associated with the most profit varied from 7 mg P/kg soil at 7 ewes/ha (10.5 DSE/ha), to 14 mg P/kg soil at 18 ewes/ha.

Three methods were compared for providing data to accompany a daily rainfall record: (i) a seasonal mean calculated from smooth curves; (ii) a seasonal mean modified by rainday effects; and (iii) actual data with missing observations filled in by method (ii). Existing plant growth models developed for the Australian tropics were used to compare the three data generation methods. These models were used to predict the number of growth days (a measure of how much plant growth would be expected in a season), green days (a measure of the duration of weight gain by rangeland cattle), runoff, and germination days. Three stations were used, one each from the monsoonal tropics, the coastal dry tropics, and the coastal subtropics. Comparatively little bias was introduced from methods (i) and (ii). Differences were greater for episodic events such as runoff and germination, than for more continuous events such as growth. There were no significant effects of generation method on calculated growth days or green days. Runoff calculated from method (i) averaged 7% lower than when actual data were used, compared with only a 3% underestimate from method (ii). The number of germination days were underestimated by between 4 and 17% when method (i) was used, compared with between a 3% underestimate and a 6% overestimate with method (ii). It was concluded that method (ii) should be used in preference to the seasonal mean alone, because of the more accurate model predictions from method (ii). A stochastic weather generator would however be required where events such as frosting would be important in risk analyses.

A detailed soil-plant-animal model was constructed and used to assess pasture and animal production at three superphosphate rates over three 15-year periods, (i) 1927–41, (ii) 1949–63, and (iii) 1972–86. At superphosphate rates of 125 and 250 kg super ha −1 yr −1 , wool production averaged 13% higher and liveweight gain 22% higher during periods (ii) and (iii) than (i). Relative fertilizer responsiveness was similar in all three periods. Climatic conditions were much harsher during the 1980's than during earlier years of period (iii). It is concluded that the period 1950–1979 was atypically wet, and that in parts of Australia where this feature applies, models should also be applied to the earlier years to obtain a more realistic understanding of climatic potential.