Effects of grazing method and fertiliser inputs on the productivity and sustainability of phalaris-based pastures in Western Victoria

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1 CSIRO PUBLISHING Australian Journal of Experimental Agriculture, 2003, 43, Effects of grazing method and fertiliser inputs on the productivity and sustainability of phalaris-based pastures in Western Victoria D. F. Chapman A,C, M. R. McCaskill B, P. E. Quigley B, A. N. Thompson B, J. F. Graham B, D. Borg B, J. Lamb B, G. Kearney B, G. R. Saul B and S. G. Clark B A School of Agriculture and Food Systems, The University of Melbourne, Vic. 3010, Australia. B Department of Primary Industries, Pastoral and Veterinary Institute, Private Bag 105, Hamilton, Vic. 3300, Australia. C Author for correspondence; d.chapman@unimelb.edu.au Abstract. 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 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 kg DM/ha.year), but significantly lower subterranean clover herbage accumulation (1440 v 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 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. Introduction The grazing industries of western Victoria have experienced cycles of growth and stagnation for the past years. Fertiliser use increased in the 1940s and 1950s, and large areas of grassland were sown to more productive species, allowing substantial increases in stock numbers. The 1970s and 1980s saw a period of decline where earlier investments were not maintained and grassland resources were depleted as productive pastures reverted to dominance of annual weed grass species (Quigley 1992; Ward and Quigley 1992) and productivity fell. Interest in productive pasture technology was revived in the early 1990s, as sharply declining terms of trade forced producers to seek ways of increasing output and reducing CSIRO /EA /03/070785

2 786 Australian Journal of Experimental Agriculture D. F. Chapman et al. costs of production. By the mid-1990s, research and extension programs had established that productive pastures based on perennial grass species and moderate to high rates of fertiliser input could markedly increase farm production and profitability in the high rainfall zone (HRZ) of western Victoria (Saul et al. 1993). Extension programs such as the Grasslands Productivity Program promoted the adoption of these technologies during the 1990s (Court 1998; Trompf and Sale 1998; Trompf et al. 1998). However, there is an on-going need for further productivity increases so that farm businesses can remain viable against a continuing trend of declining terms of trade. More productive grazing systems are required, but these systems must also meet the other requirements specified by Mason et al. (2003) in order to be sustainable. There is little scientific information on the sustainability of grazing systems in western Victoria that are based on productive pasture technologies. The failure of perennial grasses commonly used in this region, particularly perennial ryegrass (Lolium perenne L.) and the better-adapted species phalaris (Phalaris aquatica L.), to persist for significant periods of time is perceived as a serious impediment to the successful use of productive pasture technology in profitable and sustainable grazing systems (Reeve et al. 2000). There is evidence that phalaris persistence is a problem in the temperate HRZ (Virgona et al. 2000), and the solution to this problem also requires further information on the effects of management on plant populations and species herbage accumulation. Against this backdrop, the objective of the Vasey site of the Sustainable Grazing Systems National Experiment (SGS NE) was to help identify more productive and sustainable sheep grazing systems based on fertiliser inputs and grazing methods that promote phalaris growth and persistence, reduce groundwater recharge, and improve animal production. To achieve this objective, a self-contained grazing experiment with sheep comparing different levels of fertiliser input and different grazing methods was conducted on phalaris-based pastures on the Dundas Tablelands. Grazed pastures are the dominant land use on the Dundas Tablelands, and the area is known for its saline soils and high salt concentrations in streams and rivers. Previous research suggested that some form of rotational grazing can increase phalaris persistence compared with the traditional grazing method of set stocking (Morley et al. 1969; Culvenor 2000; Kemp et al. 2000; Virgona et al. 2000), and reduce soil water content during summer autumn (Clifton et al. 1996; Saul et al. 1998). Thus, a key proposition examined here was that rotational grazing would increase soil water storage capacity at the break of season, leading to lower drainage below the root zone later in the year and reduced potential for groundwater recharge compared with set stocking. The effect of management on pasture and animal production was also a key focus of the experiment, since the viability of farm businesses depends on continuous improvement in farm productivity, which is strongly related to trends in animal production. Parallel research at the same site examined the implications of higher fertiliser inputs and changes in grazing method on the quality of runoff water from pastures (Melland 2003), and the population biology of phalaris (Cullen 2002). The results of this package of research are relevant to about ha of grazed pasture throughout the phalaris subterranean clover (Trifolium subterraneum L.) zone of Victoria, plus regions in other states using similar pasture types and grazing systems. The challenge of finding more sustainable grazing systems is common to all such areas. This paper reports the key results and conclusions from the main grazing experiment. Materials and methods Site details The site was located on a commercial property in the Vasey district, near Balmoral. This region experiences predominantly winter spring rainfall, and dry, hot summers. Key details of the site location are in Andrew and Lodge (2003). The soils, formed on rhyolitic parent material, were classified predominantly as yellow sodosols (Cox et al. 1998). The soil profile was duplex, with depth to the B horizon typically cm. The soil was marginally acid [ph (CaCl 2 ) ] down to 1.4 m, and within the tolerance range of phalaris and subterranean clover (Slattery et al. 1999). Below about 1.4 m, the soil was strongly acid [ph (CaCl 2 ) ], and likely to limit root growth. A piezometer installed at the site between 1993 and 1997 recorded water table depth at about 6.5 m in late summer, rising to within 0.8 m of the surface in winter (P. Schroder and C. Clifton unpublished data). Mottling in the B horizon indicated that the soil profile becomes saturated periodically. Sown pastures were used for most of the treatments in the experiment. These pastures were sown to phalaris (cv. Australian, 4 kg seed/ha) and subterranean clover (cv. Trikkala, 8 kg seed/ha) in either May 1994 (1 replicate) or May 1995 (2 replicates). Lime was applied before sowing ( t/ha), and fertiliser was applied at sowing to supply the equivalent of kg phosphorus (P)/ha and 7 12 kg sulfur (S)/ha. A further 20 kg P/ha was applied in At the beginning of the experiment in July 1997, these pastures contained on average 47% phalaris, 31% subterranean clover, and 5% annual grass species. The annual grass species comprised mainly silvergrass (Vulpia myuros), barley grass (Hordeum leporinum) and winter grass (Poa annua). The soil Olsen P level was about 8 mg/kg. Volunteer pastures adjacent to the area of new pasture were used to provide a simple comparison of the major productivity and water use results between the 2 pasture types. The volunteer pastures were dominated by onion grass (Romulea rosea) and annual grass species, particularly silver grass, barley grass and soft brome (Bromus hordeacus). They contained no perennial grasses (apart from some occasional plants of Austrodanthonia spp.), and low levels of subterranean clover and other legumes. The soil Olsen P under volunteer pasture before the start of the experiment was 5 mg/kg. Treatments and experimental design Treatments on the sown, phalaris-based pastures compared combinations of fertiliser application (mainly P fertiliser) and grazing method, as described in Table 1 (treatments A E). An unreplicated comparison of set stocking (SS) and rotational grazing (RG) was conducted on the adjacent volunteer pasture (treatments F and G). Fertiliser treatments. Low P treatments aimed to maintain soil Olsen P under the phalaris-based pastures in the range 4 6 mg/kg, while high P treatments aimed to achieve Olsen P levels of

3 Sustainability of phalaris pastures in western Victoria Australian Journal of Experimental Agriculture 787 Table 1. Description of treatments applied at the Vasey site according to fertiliser inputs and grazing methods Treatments A E were applied to sown pastures, F and G to volunteer pastures; see text for more detailed description of grazing methods Treatment Description Fertiliser application (kg/ha) A Grazing method A SS low P Set-stocked, low P fertiliser input 24 (P) Set stocking B SS high P Set-stocked, high P fertiliser input 125 (P) Set stocking C RG 4-paddock Simple rotation, high P 125 (P) 4-paddock rotation D RG intensive Intensive rotation, high P 125 (P) Variable rotation E RG intensive + N Intensive rotation, high P + N B 125 (P) (N) Variable rotation F Volunteer SS Volunteer, control 40 (P) Set stocking G Volunteer RG Volunteer, simple rotation 40 (P) 4-paddock rotation A Total P or N applied, inclusive (see text for description of application times). B N fertiliser applied inclusive. Grazing method changed to set stocking following break of season in 2000, and returned to rotational grazing following break of season in mg/kg. Fertiliser was applied in late summer or early autumn each year before the break of season, except in the first year when it was applied in June. The amount of nutrient applied each year, and the soil Olsen P test values recorded during the experiment, are shown in Table 2. Although target P levels were not generally achieved after the sharp rise in soil Olsen P levels in 1998, the low and high P treatments differed significantly (P<0.01) in terms of the change in soil Olsen P value over time. Furthermore, the high P treatments did not differ from each other in soil Olsen P change. Thus, the treatments clearly created 2 different nutrient environments for plant growth, which was a fundamental requirement for achieving the objectives of the experiment. Nitrogen (N) fertiliser was applied as urea (46% N) to the RG intensive + N treatment in 2 dressings of 50 kg N/ha, 2 3 weeks after the autumn break and again 6 9 weeks later. This treatment was designed to test the proposition that adding N early in the growing season would stimulate pasture growth, particularly growth of the phalaris, resulting in better use of early season rainfall and a delay in the point when soils reached saturation later in the year. However, pasture growth was largely unresponsive to N fertiliser application in the 3 years in which it was applied ( ), and this treatment was discontinued after Grazing methods. Treatments were either set stocked or rotationally grazed throughout the experiment. The exception to this was the RG intensive + N treatment, which was rotationally grazed from July 1997 to April 2000, set stocked in April 2000 April 2001, then rotationally grazed until the completion of the experiment in November Sheep on set-stocked treatments (SS low P, SS high P and Volunteer SS, plus RG intensive + N in 2000) remained on plots all year, except when removed for shearing. Plots in the simple 4-paddock rotational grazing treatment (RG 4-paddock and Volunteer RG) were internally subdivided into 4 paddocks using permanent fencing. Apart from the spring period (lambing to weaning), sheep in these treatments were moved to a new paddock every 2 weeks, and returned to each paddock after a 6-week regrowth interval. During spring, the grazing and regrowth intervals decreased to 1 week and 3 weeks, respectively. Plots in the intensive variable rotation treatments (RG intensive, and RG intensive + N during and in 2001) were subdivided using temporary electric fencing to allocate pasture as required. Sheep moved to a new pasture allocation every 2 12 days depending on herbage accumulation rate, so that the length of the rotation varied according to seasonal conditions. In general, as the herbage accumulation rate increased, the speed of rotation increased (grazing duration on each pasture allocation decreased), and vice versa. The exception to this system was from the period lambing to weaning, when ewes with lambs at foot were set stocked. Experimental design. There were 3 replicate plots of treatments on the sown pastures, either 2.25 ha (SS low P) or 1.5 ha (all other sown pasture treatments) in area. Larger plots were used in the SS low P treatment in anticipation of lower stocking rates, the intention being to Table 2. Amount of fertiliser phosphorus (P) applied in each treatment per year, and corresponding average Olsen P test values in spring each year Treatments SS high P, RG 4-paddock, RG intensive and RG intensive + N also received a basal application of 30 kg K/ha in 1998; for treatment descriptions see Table 1 Treatment Fertiliser Olsen P Fertiliser Olsen P Fertiliser Olsen P Fertiliser Olsen P Fertiliser Olsen P (kg/ha) (mg/kg soil) (kg/ha) (mg/kg soil) (kg/ha) (mg/kg soil) (kg/ha) (mg/kg soil) (kg/ha) (mg/kg soil) SS low P SS high P RG 4-paddock RG intensive RG intensive + N 30 A A A Volunteer SS n.m Volunteer RG n.m A This treatment also received 100 kg N/ha in 1997, 1998 and n.m., not measured.

4 788 Australian Journal of Experimental Agriculture D. F. Chapman et al. maintain similar flock sizes of ewes in all treatments. Plots were arranged in a randomised block design. The volunteer pasture treatments had a plot size of 4.4 ha and were not replicated. Management All plots were grazed by Merino ewes (21 micron fibre diameter). Lambing began in early August, and lambs were weaned and removed from plots in late November or early December. Ewes were shorn in June 1998, and thereafter the shearing date was moved forward by about 1 month each year. Stocking rate was adjusted (if necessary) on each plot during the year (average 3.3 times per year) according to herbage mass and average ewe liveweight on each plot. The average change in stocking rate on each occasion was 1.5 ewes/ha. The intention was to, as far as possible, maintain common ewe liveweights across treatments on the phalaris-based pastures, and also achieve pasture mass at lambing and weaning of kg DM/ha and kg DM/ha, respectively. Ewes on most plots received sufficient supplementary feed (triticale grain) during summer and autumn to ensure they remained above a condition score of 2.0. Measurements Measurement procedures generally followed the protocols described by Andrew and Lodge (2003). Climate data were recorded at an automatic station located within the experimental site, from early June Before this date, daily rainfall data were obtained from a manual rain gauge 400 m from the site. This is the same location for which long-term rainfall data were collected (Table 3). In September 1998, a second automatic weather station was installed on the runoff plots adjacent to the main experiment (Melland 2003). Rainfall data from this station were used in preference to the data recorded at the main climate station, since the rain gauge was not affected by wind velocity and turbulence to the same extent as the rain gauge on the main site. Volumetric soil moisture content was measured using a calibrated neutron moisture meter (NMM), at 20-cm intervals down to 120 cm depth. Measurements were taken 8 12 times per year from February 1998 to March The deepest NMM reading was assumed to represent soil moisture to a depth of 140 cm. Plant available soil P was estimated using the Olsen test, in samples collected in September or October each year, except in 1997 when they were collected in June before the fertiliser application. Herbage accumulation rate was measured by difference between herbage mass under grazing exclusion cages (0.5 m 2 ), from July 1997 to November There were 20 or 24 cages per plot, and cages were moved every 3 6 weeks during the growing season, depending on conditions for growth. No measurements were taken during summer due to dry conditions. Herbage mass was measured with a calibrated weighted disk meter (Cayley and Bird 1996). Herbage mass measurements included both standing dry matter and litter. Botanical composition was measured using BOTANAL, following the procedures described by Andrew and Lodge (2003). Measurements were taken every 4 weeks from July 1997 to November At each time of measurement, 24 quadrats (0.1 m 2 ) were used for analysis in each plot. Stocking rates were calculated for the period between shearing each year. The stocking rate reported here is a weighted average of the number of animals per plot per day for each reporting period, converted to per hectare values. Lamb liveweights were recorded at marking, and again at weaning. Lamb production per hectare was calculated as average stocking rate (ewes/ha) multiplied by average weaning weight (kg/ewe). The latter term takes into account weaning percentage. Statistical analysis A linear mixed model including a cubic spline of time (Verbyla et al. 1999) was fitted to data for soil water deficit, herbage accumulation rate and herbage mass to test for effects of treatments, allowing for random plot effects. The data for species herbage accumulation and for all animal variables were analysed by ANOVA. Data were transformed to logarithms before analysis and means back-transformed after analysis. All analyses were undertaken using Genstat 5.42 (GenStat Committee 2000). Economic analysis The economic analysis described by Barlow et al. (2003) was used to compare the equivalent annual net returns that could be expected from each of the pasture systems tested. The analysis used data for stocking rates, lamb weaning weights, wool yields and supplementary feed requirements collected from the experiment between 1998 and Results Climatic conditions Total annual rainfall during the experiment was usually below the 48-year average for the locality (Table 3). Summers were typically dry, with the break of season generally occurring in May or June, except in 2001 when the break occurred in early April. Volunteer pastures Mean values for some of the major productivity and water use variables in the set-stocked and rotationally grazed volunteer pastures are presented in Table 4, for comparison with results from the sown pastures, which are presented below. While total annual herbage accumulation from these pastures was comparable to the phalaris-based pastures (see below), this herbage was produced over a shorter growing season and was of much lower nutritive value. Hence, these pastures were unable to support high stocking rates and the level of per-animal production was low. Overall, pasture utilisation was also low, leading to problems of surplus herbage mass in late spring. It was not possible to compare the grazing method treatments statistically since they were not replicated. Table 3. Monthly rainfall (mm) recorded at the experimental site, and long-term mean monthly rainfall totals recorded 400 m from the site from 1953 to 2001 Year Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Total Long-term mean

5 Sustainability of phalaris pastures in western Victoria Australian Journal of Experimental Agriculture 789 Table 4. Mean productivity and water use characteristics of volunteer pastures either set stocked or rotationally grazed, inclusive Variable Set stocked Rotationally grazed Maximum soil water deficit at cm depth (mm) Total herbage accumulation (kg DM/ha.year) Average herbage mass (kg DM/ha) July November Botanical composition in winter (%DM) Annual grass species A Onion grass Subterranean clover 6 3 Other species 6 2 Stocking rate (ewes/ha) Lamb weaning liveweight (kg/head) Lamb production (kg liveweight/ha) A Principally silver grass, barley grass, and soft brome. However, there appeared to be few strong differences in any of the variables between the set-stocked and rotational-grazing treatments applied to the volunteer pastures. Sown pastures Soil water deficit. Modelled cubic splines for February 1998 March 2001 (Fig. 1) revealed a significant (P<0.001) linear effect of treatment, and a significant (P<0.05) non-linear effect of treatment spline (day). Only data for cm were used for this comparison, because evidence from gravimetric soil sampling at the site indicated that 20 cm NMM readings underestimated soil water deficits in the top 20 cm of the soil by up to 30% (M. McCaskill unpublished data). Soils reached saturation under all treatments in winter 1998, but were not saturated at any stage during Soils approached saturation again during winter spring The non-linear treatment day effect was due to greater soil water deficits under the SS high P and RG 4-paddock treatments in summer, a consistent trend across all 3 years. However, the difference between treatments in the maximum soil water deficit was only 14 mm between the driest and wettest treatments over the 3 years. Herbage accumulation rate and herbage mass. There were significant linear treatment (P<0.001) and day (P<0.001) effects for herbage accumulation rate from May 1998 to November Herbage accumulation rate increased with time; average total annual pasture herbage accumulation was 7150, 7600, and 9910 kg DM/ha in 1998, 1999 and 2000, respectively. There was a significant (P<0.05) non-linear effect of day, but no significant Soil water deficit (mm) July Jan July 1998 Jan July 1999 Jan July 2000 Jan Figure 1. Fitted cubic splines of soil water deficit (mm) between 20 and 140 cm of soil profile depth, for 5 combinations of fertiliser input and grazing method applied to phalaris-based pastures in Western Victoria. SS low P ; SS high P ; RG 4-paddock -- ; RG intensive ; RG intensive + N.

6 790 Australian Journal of Experimental Agriculture D. F. Chapman et al. treatment spline (day) effect, showing that herbage accumulation rate of all treatments responded similarly to seasonal conditions. Overall, the rate of herbage accumulation in the SS low P treatment was lower than the accumulation rate of all other treatments (data not shown). Fitted cubic splines for herbage mass are presented in Figure 2. Herbage mass was mostly in the range kg DM/ha for each 12-month period, and within the range kg DM/ha for the period from the break of season until mid-spring in each year. There was a significant (P<0.05) non-linear effect of treatment spline (day), due to a trend toward higher herbage mass in rotationally grazed treatments from the break of season until mid-spring. This effect was most apparent in 1998 and, especially, 2000, when the RG 4-paddock and RG intensive treatments accumulated an additional kg DM/ha compared with all other treatments from May until September (Fig. 2). The RG intensive + N treatment, which was previously rotationally grazed, was set stocked in 2000 and therefore followed the SS low P and SS high P treatments during this period, whereas it followed the RG 4-paddock and RG intensive treatments in 1998 and 1999 (Fig. 2). In general, the SS low P treatment had the lowest herbage mass of all treatments, while the RG 4-paddock treatment tended to have the highest mass. Species herbage accumulation. Sown pastures comprised mainly phalaris (5 85% of herbage mass, depending on year and treatment), subterranean clover (15 45%) and annual grasses, particularly silvergrass and barley grass (collectively 15 25%). Other species were important in some instances [notably capeweed (Arctotheca calendula) in set-stocked pastures], but were generally minor components (<5% of total herbage mass). The total annual herbage accumulation of the main pasture constituents in each year of the experiment is presented in Table 5. Significant effects of treatment (P<0.05) were recorded in all years for phalaris, subterranean clover and capeweed, except for subterranean clover and capeweed in No significant effects of treatment were recorded for annual grass herbage accumulation. Rotational grazing clearly favoured phalaris and reduced clover growth, whereas set stocking reduced phalaris and favoured clover growth. By 1999, treatments had clearly separated according to grazing method: pastures that were rotationally grazed produced an additional kg of phalaris DM/ha compared with pastures that were set stocked, but lost about 1000 kg DM/ha of subterranean clover compared with pastures that were set stocked (Table 5). The effects of changing the management of the RG intensive + N treatment from rotational grazing to set stocking in 2000 are clearly seen in the high subterranean clover herbage accumulation measured in that year, and a concomitant fall in phalaris production. Effect of fertiliser alone on species herbage accumulation was apparent from Pasture mass (kg DM/ha) July 1997 Dec July 1998 Jan July 1999 Jan July 2000 Jan Figure 2. Fitted cubic splines of herbage mass (kg DM/ha) for 5 combinations of fertiliser input and grazing method applied to phalaris-based pastures in Western Victoria. SS low P ; SS high P ; RG 4-paddock -- ; RG intensive ; RG intensive + N.

7 Sustainability of phalaris pastures in western Victoria Australian Journal of Experimental Agriculture 791 Table 5. Net herbage accumulation (kg DM/ha.year) of four pasture components for five combinations of fertiliser input and grazing method applied to phalaris-based pasture in Western Victoria over four years Within each row, means followed by the same letter are not significantly different (l.s.d. at P = 0.05); for treatment descriptions see Table 1 SS low P SS high P RG 4-paddock RG intensive RG intensive + N Signif Annual grasses n.s. Capeweed n.s. Phalaris 1150a 1490b 2110c 1580a 1930b * Subterranean clover n.s Annual grasses n.s. Capeweed 350b 310b 170b 910b 10a * Phalaris 1730a 2400b 4620c 3690c 4610c *** Subterranean clover 2560d 2140c 1460a 1870bc 1500ab * 1999 Annual grasses n.s. Capeweed 1100c 960c 190b 1070c 10a *** Phalaris 1720a 2880b 4760c 3760bc 4550c *** Subterranean clover 2740b 2450b 1540a 1590a 1550a * 2000 Annual grasses n.s. Capeweed 2410cd 2590d 320b 1220c 40a ** Phalaris 1440a 1590a 4780d 3350c 2380b *** Subterranean clover 3340d 2740c 1870b 1060a 3740d *** *P<0.05; **P<0.01; ***P<0.001; n.s., not significant. the comparison between the SS low P and SS high P treatments. In general, higher fertiliser application increased phalaris herbage accumulation and reduced subterranean clover herbage accumulation. However, the magnitude of the difference between low and high fertiliser within the 2 set-stocked treatments was less than the magnitude of the difference between set stocking and rotational grazing at high rates of fertiliser input, especially when the comparison was made between the SS high P and the RG 4-paddock treatments (Table 5). Capeweed herbage accumulation was lower in the RG intensive + N treatment than in all other treatments in (Table 5). There was no significant effect of treatments on the growth of annual grasses in any year of the experiment. Herbage accumulation of capeweed and annual grass species increased in all treatments during the experiment, except for capeweed in the RG intensive + N treatment. Animal production. Stocking rate increased over time in all treatments (Table 6). The magnitude of this increase, calculated using the period April 2000 March 2001 as the final year (since March 2001 to November 2001 was an incomplete year and encompassed the growing season only) ranged from 11% for the RG 4-paddock treatment to 28 30% for the other sown pasture treatments. Significant differences between treatments in stocking rate were recorded in all years (Table 6). These differences reflected both the quantity and quality of feed grown, since Table 6. Stocking rate (ewes/ha) supported by pastures under five combinations of fertiliser input and grazing method applied to phalaris-based pastures in Western Victoria over five years Within each row, means followed by the same letter are not significantly different (l.s.d. at P = 0.05); for treatment descriptions see Table 1 Time period SS low P SS high P RG 4-paddock RG intensive RG intensive + N Signif. July 1997 June a 11.7b 14.1c 12.3b 12.0b *** June 1998 May a 10.7a 13.7b 13.9b 15.8b ** May 1999 April a 13.2b 14.2b 14.6bc 15.8c *** April 2000 March a 15.2b 15.6b 15.9b 15.4b ** March 2001 November a 15.9b 16.1b 16.7b 17.4b *** **P<0.01; ***P<0.001.

8 792 Australian Journal of Experimental Agriculture D. F. Chapman et al. animal numbers per plot were adjusted 3 or 4 times per year in an attempt to maintain common ewe liveweights among treatments through control of pasture allowance (see Materials and methods). Therefore, stocking rate was an emergent property of the pasture productivity of each system, combined with the criteria applied to the adjustment of animal numbers. In the first 2 years, grazing method appeared to have a greater effect on stocking rate than fertiliser input. For example, in the year, there was no difference between the 2 set-stocked treatments in stocking rate, whereas the rotationally grazed treatments all had higher stocking rates than the set-stocked treatments. However, in the last 2 years of the experiment, higher fertiliser input under set stocking clearly allowed a higher stocking rate to be carried (compare the SS low P and SS high P treatments, Table 6), and there was no significant difference between the SS high P treatment and the rotational grazing treatments. Lamb production per hectare did not differ between treatments, except in 2001 when the SS high P and RG 4-paddock treatments (588 and 524 kg lamb liveweight/ha, respectively) were higher (P<0.05) than the SS low P treatment (394 kg liveweight/ha). The other treatments were intermediate and not significantly different from all other treatments. There was a trend (P = 0.08) toward higher lamb production per hectare in 1998 under rotational grazing (mean of RG treatments: 435 kg/ha) than set stocking (mean: 383 kg/ha). Mean lamb production per hectare for the 5 years ( ) was 352 kg/ha for SS low P, 425 kg/ha for SS high P, 442 kg/ha for RG 4-paddock, 443 kg/ha for RG intensive, and 407 kg/ha for RG intensive + N. Discussion Water use and balance A core proposition tested in this experiment was that some form of rotational grazing applied to pastures based on the deep-rooted grass phalaris would increase the growth of this perennial species leading to greater winter soil water storage capacity and therefore improved control of groundwater recharge compared with set-stocked pastures. However, this proposition was not supported by the results. While the growth of the perennial species was enhanced by rotational grazing, there was no consistent relationship between grazing method and maximum soil water deficit. The strongest deficits developed in the set-stocked high fertility and 4-paddock rotation treatments, while the 2 tactical rotational treatments were not significantly different from the low fertility set-stocked control (Fig. 1). These results are contrary to those of Clifton et al. (1996) who, at the same site, found that rotational grazing increased soil matric potential in summer autumn relative to set stocking. Two reasons can be offered as to why the earlier results were not supported by this study. First, using the soil moisture characteristic curve reported by Melland (2003), the differences in soil matric potential of Clifton et al. (1996) translate into only small differences in volumetric soil water content. Second, the soil has a high but spatially variable gravel content (20 40% by volume) in the subsoil (Cox et al. 1998). The relatively small treatment differences may be difficult to detect against background variability in gravel content. While soil moisture profile data are based on NMM readings down to only 120 cm depth, this information gives a reasonably accurate picture of total water extraction, since Melland (2003) estimated the depth of the rooting zone at this site to be about 140 cm from NMM readings taken down to 180 cm. This rooting depth coincides with the point at which the subsoil becomes strongly acid (Cox et al. 1998). Maximum soil water deficits reported in this study were mm, compared with mm from other studies in south-eastern Australia (e.g. Ridley et al. 1997; Dolling 2001; Heng et al. 2001; Whitfield 2001). There are 2 reasons for this difference. First, only the deficit in the cm layer was reported here because NMM readings at 20 cm depth did not reliably estimate deficits in the top 20 cm. When frequency domain reflectometer measurements in this layer are combined with NMM data for cm, a maximum soil water deficit of close to 100 mm is predicted (M. R. McCaskill unpublished data). Second, the soil had a high gravel content, with the >2 mm fraction comprising 40% of soil volume between 50 and 140 cm depths (Cox et al. 1998). Thus, there is limited capacity for water storage within the subsoil at this site. The only components of the water balance that were measured directly in this experiment were rainfall and soil moisture. Simulation studies of water balance at the site have been conducted by Simpson et al. (1998), using the SWIMv2 model of soil water balance coupled to the GrassGro model of pasture growth, and by White et al. (2003), using the Sustainable Grazing Systems Pasture Model (Johnson et al. 2003). There is reasonable agreement between the results of these 2 modelling exercises, with both predicting about 110 mm deep drainage per year (about 17% of mean annual rainfall) under phalaris subterranean clover pasture, irrespective of grazing method. The models predict higher drainage under an annual pasture, at about mm per year. The models also predict no difference in deep drainage between grazing methods, a conclusion supported by the soil water deficit data collected during the experiment (Fig. 1). The original proposition concerning water use that was examined in this experiment relied on the assumption that sufficient growth of the perennial grass would occur during summer and autumn to draw moisture from the subsoil layers, and therefore create increased capacity to store winter spring rainfall. It also assumed that rotational grazing would increase summer autumn growth of phalaris compared with set stocking. Phalaris was the only species present in the pastures that could grow in summer, since all

9 Sustainability of phalaris pastures in western Victoria Australian Journal of Experimental Agriculture 793 other species were either annuals, or strongly dormant perennials. Rainfall during the 3 calendar years when the soil moisture profile was monitored ( ) was consistently 8 9% below average (Table 3). Some phalaris growth occurred in most summers, but the amount of green herbage produced was small and could not be measured against a backdrop of declining herbage mass caused by the accelerated transfer of plant material from dead to litter. Maximum soil water deficit in summer autumn was similar for all 3 years. Within the constraints imposed by the climatic conditions experienced during the study, these results suggest that there are limited opportunities for using grazing management during summer in this environment to manipulate leaf area and water extraction, since the amount of summer growth that is possible from phalaris is simply too low to influence soil water content. The high stocking rates applied in this experiment, especially in the rotationally grazed treatments in the early years, may also have restricted water use by the pasture during the late spring summer period. Simpson et al. (1998) predicted that at least 1.8 m of soil would need to be dried to wilting point before the autumn rains began to prevent drainage under pasture in an average year at the Vasey site. The effective rooting depth of phalaris at the site was only 140 cm (Melland 2003), and its summer activity was low, therefore this threshold was not met under any of the management treatments studied. Clearly, sole reliance on productive phalaris-based pastures will not substantially control groundwater recharge on these soils. Plants that are more summer-active and have a much deeper root system may have some impact, as seen with kikuyu at the Albany site (Sanford et al. 2003b). Simpson et al. (1998) predicted that a mature woodlot would reduce deep drainage at the Vasey site to 13 mm per year and therefore that the strategic planting of trees in the landscape would offer an effective solution to the problem of controlling deep drainage. However, this land-use change may seriously compromise farm business profitability and will not be a viable option in all instances. There is a clear need for further research into the adaptation and breeding of deep-rooted, summer-active pasture or forage species that can help solve the problem of excess deep drainage without cutting off future productivity options for livestock producers. Pasture productivity Despite generally below-average rainfall during the experiment, pastures supported high stocking rates and lamb production levels. Assuming the Merino ewes used on the experiment were equal to 1.5 dry sheep equivalents (DSE), then the carrying capacity of the phalaris-based pastures ranged between 0.85 and 2.51 DSE/ha for every 25 mm annual rainfall in excess of 250 mm. The equivalent range for the volunteer pastures was DSE/ha per every 25 mm in excess of 250 mm. The highest values occurred in , when rainfall was low (486 mm for the period May 1999 April 2000). However, these values probably overestimate the sustainable carrying capacity of the pastures since they applied for a limited time only. Using data from a range of grazing experiments in South Australia, French (1987) proposed that it was possible to carry 1.3 DSE/ha per 25 mm of average annual rainfall in excess of 250 mm/year. This model was supported by the Grasslands Productivity Program (GPP), which collected information on carrying capacity for pastures receiving low or high fertiliser inputs from over 200 farms in south-eastern Australia (Court 1998). The GPP revealed 2 relationships between carrying capacity and annual rainfall: one for low fertility pastures at about 0.8 DSE/ha per 25 mm in excess of 250 mm, and one for high fertility pastures at about 1.3 DSE/ha per 25 mm in excess of 250 mm (Court 1998). This experiment showed that, with responsive pasture management applied to sown pastures, including the ability to adjust animal numbers occasionally in response to feed supply and animal condition, it is possible to carry more than 2 DSE/ha per 25 mm in excess of 250 mm. However, the sustainable level is likely to be less than this. All the 16 observations available for the 4 high fertiliser treatments on phalaris-based pastures in 4 years (from to ) exceeded 1.3 DSE/ha per 25 mm in excess of 250 mm. The average of these 16 observations, 1.8 DSE/ha per 25 mm in excess of 250 mm, is probably closer to the sustainable maximum carrying capacity for phalaris-based pastures in the HRZ of south-eastern Australia. Further analysis of the relationships between environmental factors and pasture and animal production is presented in the theme papers for pastures (Sanford et al. 2003a) and animal production (Graham et al. 2003). Across all of the sites in the SGS NE, Graham et al. (2003) found no relationship between total annual rainfall and stock carrying capacity. This reflects the wide range of climatic conditions and pasture types embraced by the SGS NE. Better relationships were obtained when months with stored water in the soil or length of the growing season were used as independent variables (Sanford et al. 2003a; Graham et al. 2003). These findings are consistent with Saul and Kearney (2003) who re-analysed data from the GPP and found that, for paddocks less than 20 ha in area, the relationship DSE/ha = (growing season months) (Olsen P) explained 71% of the variation in stocking rate for paddocks receiving high fertiliser inputs. Using the Saul and Kearney (2003) relationship, the estimated mean carrying capacities for the SS low P, SS high P, RG 4-paddock, RG intensive and RG intensive + N treatments over the 5 years of this experiment were 17.7, 19.5, 19.5, 19.2 and 19.4 DSE/ha, respectively. Actual mean stocking rates for the respective

10 794 Australian Journal of Experimental Agriculture D. F. Chapman et al. treatments were 16.2, 20.0, 22.1, 22.1 and 22.9 DSE/ha (assuming 1 ewe = 1.5 DSE, Table 6). Thus, the Saul and Kearney (2003) relationship was a good predictor of stocking rate in the SS high P treatment, which most closely resembles the pastures from which the relationship was derived. However, it slightly overestimated (by 8%) the stocking rate for the SS low P treatment, and underestimated (by 13 18%) the carrying capacity for the rotationally grazed pastures. Nevertheless, relationships between stocking rate and length of the growing season (plus other factors) are clearly more useful than relationships using total annual rainfall. Such relationships fit well with the results recorded here, and reveal substantial potential to raise carrying capacity through the application of the full suite of pasture improvement technologies productive species, fertiliser, increases in stocking rate, and changes in grazing method to make better use of growing season rainfall. Realising this potential is important for the continued viability of grazing enterprises in western Victoria. Stocking rates applied in this experiment were an emergent property of herbage accumulation rate, combined with decisions about animal numbers made on a plot-by-plot basis. The aim of these decisions was to keep ewe liveweights constant across all treatments on phalaris-based pastures, and to keep herbage mass within a target range. Pasture allowance was manipulated through the removal or addition of animals on individual plots when liveweights or herbage mass deviated from targets. In livestock production systems, stocking rate is a trade-off decision between several factors, including herbage accumulation rate, herbage mass, and target levels of animal performance. Therefore, measures of pasture productivity based on potential carrying capacity, such as those discussed above, should be treated with further caution, since the trade-offs made in selecting a stocking rate may differ from case to case. Some of the shortcomings of using stocking rate as the measure of animal performance can be overcome by using actual yields of animal product, since these are likely to integrate the effects of pasture quality and quantity. In this experiment, lamb production per hectare was measured. Lamb production was a function of ewe stocking rate, weaning percentage and lamb growth rate (weaning liveweight). The ability to carry more ewes per hectare under rotational grazing than under set stocking was countered by poorer lamb weaning weights (Thompson et al. 2001), presumably due to poorer pasture quality. Thus, there were few significant differences between grazing methods in lamb production per hectare. Production per hectare is generally closely related to farm profitability (Beattie and Hamilton 2000). Highest lamb production recorded throughout the experiment came from the SS high P treatment in 2001, when a combination of an early break of season, followed by mild winter conditions, allowed high herbage accumulation rates and a good balance between feed supply and demand. This was coupled with high subterranean clover content (Quigley et al. 2000), and therefore likely excellent feeding value of pasture. Under these conditions, there appears to be little benefit in using rotational grazing to increase animal production. However, such conditions occur infrequently, and a major benefit of rotational grazing is the additional ability it provides for control of pasture allocation and feeding. This in turn allows greater control over the balance between feed supply and demand in systems characterised by high seasonal and year-to-year variability. These points lead to the conclusion that no single grazing method will optimise the system under all conditions, and that a combination of grazing methods applied in such a way as to exploit the strengths of each and minimise their weaknesses will give best results. Pasture species herbage accumulation The effect of management treatments on the persistence and growth of phalaris was a key focal point in this experiment, since the propositions that were tested revolved around the extent to which management was able to influence the productivity of the perennial grass component of pastures. A clear and consistent result of the experiment was that rotational grazing led to a higher level of phalaris herbage accumulation (Table 5) than did set stocking. This result is consistent with previous work that has demonstrated the importance of resting from grazing for survival and productivity of different phalaris genotypes in a range of environments (Morley et al. 1969; Hill 1989; Culvenor 1994; Lodge and Orchard 2000; Virgona et al. 2000). Stronger growth of phalaris under rotational grazing was due to a larger tiller (and, presumably, plant) size than that under set stocking (Cullen 2002). The other key components contributing to herbage accumulation, leaf appearance rate and tiller density (Lemaire and Chapman 1996), did not differ between treatments (Cullen 2002). Similar results were obtained by Morley et al. (1969). Imposing a controlled interval between grazing evidently allows phalaris to allocate more growth resources to above-ground growth, therefore strengthening its competitive position within the pasture community. While rotational grazing favoured phalaris growth compared with set stocking, the reverse was the case for subterranean clover. Subterranean clover herbage accumulation increased under set stocking during the experiment, particularly within the first 2 years, whereas it remained steady and relatively low under rotational grazing (Table 5). It is difficult to clearly determine cause from effect in this result, but the sequence of events appears to be that, as phalaris growth increased in response to rotational grazing, subterranean clover growth was held in check, presumably due to competition between the established perennial grass and establishing subterranean clover