An on-farm evaluation of the capability of saline land for livestock production in southern Australia

An on-farm evaluation of the capability of saline land for livestock

production in southern Australia

D. T. Thomas

, C. L. White

, J. Hardy

, J.-P. Collins

, A. Ryder

and H. C. Norman

WA 6913, Australia.

B_{Department of Agriculture and Food Western Australia, Albany, WA 6330, Australia.} C_{Department of Agriculture and Food Western Australia, Katanning, WA 6317, Australia.} D_{Future Farm Industries CRC, The University of Western Australia, Crawley, WA 6009, Australia.} E_{Corresponding author. Email: dean.thomas@csiro.au}

Abstract. Grazing livestock on revegetated saline land is one of few profitable options to continue using this class of agricultural land. However, there has been little research conducted to assess the capability of saline land to support livestock production based on the soil and water characteristics at a particular site. In this study, data from 11 grazing studies collected from eight commercial farms across southern Australia were used to estimate metabolisable energy (ME) utilised/ha, as well as total ME produced/ha. All data were from the autumn (March–May) period, when feed is normally in short supply and of limited quality. Site characteristics indicative of the severity of salinisation varied across the sites. Topsoil electrical conductivity (ECe) ranged from 1 to 33 dS/m and groundwater EC from 14 to 60 dS/m (equivalent to sea water). Feed on offer before grazing varied from 700 kg dry matter/ha to 9000 kg dry matter/ha between sites.Thinopyrum ponticum and

Puccinellia ciliatafeatured prominently in the less saline revegetated sites, withAtriplexspp. present on the more saline sites and some lucerne and rhodes grass on the less saline, well drained sites. Grazing days per ha for sheep (ME-adjusted dry sheep equivalent) on autumn pastures across the sites ranged from 41 to 3600, and liveweight gains ranged from–95 to 314 g/sheep. day. The grazing value of the highest producing saltland was at least as high as that expected on adjacent areas that were not salt affected.

The major advantage of establishing saltland pastures included an out-of-season feed supply high in crude protein and micronutrients that possessed the ability to capture summer and autumn rain. This should represent a substantial reduction in supplementary feed costs and increases theflexibility of methods for feeding livestock through periods of low annual pasture availability. The value of the ME produced on the highest yielding saltland pasture was estimated to be $360/ha based on substituting the best alternative strategy of purchasing lupin grain as a supplement. A quadratic relationship (R2= 0.62,P= 0.024) was found between soil ECe and ME produced across the sites. Significant relationships were not found between other saline site characteristics and ME production, which partly reflects the complexity of these systems as well as limitations with site characterisation.

Introduction

Land salinisation reduces vegetation growth and thus forage growth in salt-affected soils, through a range of mechanisms, including osmotic and ionic stress (Hasegawa et al. 2000), decreased stomatal conductance (Seemann and Critchley 1985) and nutrient toxicity and deficiency associated with anoxia (Barrett-Lennard 2003; Steffens et al. 2005). The nutritive value of vegetation may also be lower because the diversity of forage species that will grow on saline land is reduced, and some mechanisms used by plants to adapt to a saline environment (e.g. salt accumulation) result in forage that is nutritionally imbalanced for livestock; for example, high levels of sodium, potassium, chloride and plant secondary compounds, and low levels of calcium, copper and zinc inAtriplexspp. (Masterset al. 2007). However, loss of productivity on saline sites may be reduced by the introduction of productive, salt-tolerant plant species that use soil water available in salt-affected areas and

by providing combinations of feed with complementary nutritive characteristics (Thomas et al. 2007b). The capability of salt-affected land for animal production can be approximated in terms of the energy produced that can be metabolised by the grazing animal per unit area (MEP, MJ/ha).

There have been few attempts to determine how the characteristics of saltland pasture systems are related to the livestock production capability of a particular site. However, it is accepted that loss of productivity in saltland pastures is related to a wide range of site characteristics including soil type, soil salinity and sodicity, ground water salinity, ground water depth, rainfall and the presence of salt-tolerant species in the system. In this paper, site and vegetation characteristics, and the estimated MEP in eight saltland pasture sites that were grazed in southern Australia are reported. Metabolisable energy utilised (MEU, MJ/ha) was determined and an adjustment for grazing intensity was applied to calculate MEP. We hypothesised that forage

biomass, nutritive value and MEP would be related to the environmental characteristics we measured.

Materials and methods

Sites and locations

Eleven grazing studies were conducted on eight saltland pasture sites, which were established on commercial properties as part of a larger network of demonstration sites through the Sustainable Grazing of Saline Land (SGSL) project (SGSL site references are provided in Table 2 and more information is available at http:// spatial.agric.wa.gov.au/sgsl/, verified 11 November 2008). The 11 grazing studies were selected from a larger group of studies on the basis that grazing and site characterisation data could be obtained and used to determine relationships between forage biomass, feeding value and ME produced. Each grazing study comprised grazing of a single experimental paddock under set stocking until the livestock were removed. Descriptions of location, climate, rain, land area, soil characteristics, two measures of soil salinity; electrical conductivity of saturated soil extract (ECe), derived from EC 1 : 5 in the top 20 cm (Hunt and Gilkes 1992), and apparent electrical conductivity (ECa), derived from maps generated using an EM38 electromagnetic induction meter (Hunt and Gilkes 1992), pasture establishment methods and species were recorded at each site. Feed on offer (total aboveground edible biomass), periods of grazing, stocking rates, reasons for start and end points for grazing, and animal liveweight before and after grazing were recorded for each grazing study.

Forage species

The SGSL project established new forage species on the sites between 2002 and 2004 with an aim to improve forage production by introducing productive salt-tolerant plants. The introduced forage species were combinations of perennial grasses [Chloris gayanaKunth cvv. Callide, Kantambora, Finecut and Topcut,

Festuca arundinaceaSchreb. cv. Advance,Panicum coloratumL. (var. makarikariense) cv. Bambatsi, Panicum maximum Jacq. cv. Gatton, Brachiaria decumbens Stapf., Setaria sphacelata

(Schum.) Moss cv. Splenda, Thinopyrum ponticum (Podp.) Z. W. Liu and R. R. C. Wang cvv. Tyrrel and Dundas and

Puccinelliaciliata(Bor)],legumes(MedicagosativaL.cv.Sequel,

Trifolium michelianumSavi cv. Frontier), saltbushes [Atriplex amnicola Paul G. Wilson, A. nummulariaL.,A. semibaccata

R.Br., A. undulata D. Dietr. and Maireana brevifolia(R.Br.) Paul G. Wilson] and Acacia saligna (Labill.) H. Wendl. Introduced forage species were generally sown by direct seeding. Some saltbushes were established as seedlings, sown using a commercial tree planter (e.g. Ezy Planter 2000, Chatfield Enterprises, Western Australia). Typically, a wide range of perennial species were sown in order to match the wide niche diversity with the most productive plants, although characteristics of individual sites were also considered.

ME calculations

Animal liveweight and weight change were used to calculate grazing MEU on the sites for the duration of grazing. Since different stocking rates and classes of animals were used in different experiments, animal performance was standardised in

terms of MEU (MJ ME/ha; Eqn 1) or ME-adjusted‘dry sheep equivalent’grazing days (DSEadj; Eqn 2).

MEU¼MEmaintenanceþMEwt gain or loss ð1Þ DSEadj-days¼MEU=8:8 ð2Þ For this purpose, a DSEadj-grazing day was equivalent to 8.8 MJ ME, which is the ME required for maintenance of a 50-kg Merino wether of medium breed size consuming a diet of 10 MJ ME/kg dry matter (Standing Committee on Agriculture 1990).

Maintenance ME was calculated using Eqn 3 derived from Grassgro (www.hzn.com.au/grassgro.php) predictions for a medium-sized sheep breed with a standard reference ewe liveweight at maturity of 50 kg:

MEmaintenance¼1:42þ0:15ðliveweight in kgÞ ð3Þ While basal metabolic rate is a function of metabolic liveweight (W0.75), the predicted relationship between MEmaintenanceand liveweight was found to be effectively linear due to adjustments for energy expenditure associated with movement during grazing, which increases with liveweight.

Energy gained or lost during weight gain or loss (MEwt gain or loss) was calculated byfitting a curve using the computer program Tablecurve3D V4 (Systat Inc., Richmond, CA) Eqn 4 on Grassgro predictions:

Y¼aþbf1EXPðcðLWTfÞÞ

d=ðdþeÞ ð1þ ½cEXPððdþeÞðLWTfÞÞ ðdþeÞEXPðcðLWTfÞÞ=ðdþecÞÞg ð4Þ where Y = MEgainor MEloss[MJ/kg LWT change(kg)]. For weight gain: a = 51.02, b = 20.62, c = 0.056, d = 0.035, e = 0.044, f = 29.8. For weight loss: a = 27.4, b = 11.08, c = 0.056, d = 0.035, e = 0.044, f = 29.8.

While it is accepted that the use of a standard feed quality will lead to bias in situations where feed is consistently of a higher or lower ME than 10 MJ/kg, in practice the simplification of estimation more than accounts for loss of accuracy. Comparisons of MEU made using the equations above (Table 1) with those using Grassgro show differences of less than 5% when taken over an annual grazing cycle.

MEP was calculated using the computer program Tablecurve3D V4 using MEU values and input data derived from a Grassgro simulation using a perennial grass (Eqn 5). The MEP calculation created a standardised estimated feeding value for each saltland pasture. The model assumes there is no difference in rate of depletion among pasture types.

MEP¼MEUð0:5130:735=s4:084w0:923=s2

15:011w2þ8:013w=sþ1:264=s338:203w3

þ14:484w2=s5:219w=s2Þ ð5Þ

wheres= stocking rate (DSE/ha) andw= liveweight gain (g/day).

Statistical analysis

Multiple linear regression analysis was used to determine correlations between the ME produced (response variate) and

site characteristics, collectively, and polynomial regression analysis was used to determine individual correlations. All analyses were conducted using the GENSTATstatistical package (GENSTAT2003).

Results

General observations

Several classes of livestock were grazed on the sites, although they were predominantly 6-month to 2-year-old Merino sheep. All sites were grazed over the autumn to early winter (March–June) period. The decision to de-stock plots depended on the age of the sheep; weaner sheep tended to be removed as soon as they started losing weight, while older sheep were taken off the plots after no feed of value remained, as determined by visual assessment of the pasture. Perceived sensitivity of some species to permanent damage from grazing was considered in the decision of when to remove stock (usually in recently established plots, or those containing small shrubs). The grazing intensity

across the sites varied widely because of the different reasons for de-stocking the plots. Consequently, pasture utilisation (MEU) across sites was affected by different grazing intensities and an adjustment was necessary to make comparisons between the sites (an MEP calculation was made to compare pasture productivity across sites).

Site characteristics

There was a weak positive relationship between ECe and ECa (R2= 0.35). Mean site ECe in the topsoil ranged from 112 to 3263 mS/m and ECa ranged from 31 to 126 mS/m. Water table depth across the sites ranged from 0.2 to–3.8 m and water EC ranged from 1400 to 6000 mS/m. There was a poor relationship between soil and water EC.

Grazing value of saltland pastures

The food on offer produced across the sites ranged from 699 kg/ha on aM. sativa-sown plot to 9037 kg/ha on aF. arundinaceaand

T. ponticum-dominant plot.P. ciliateandT. ponticumfeatured

Table 2. Livestock class, stocking rate, liveweight gain and metabolisable energy (MEU and MEP)-derived grazing days of producer network saltland demonstration sites in Western Australia (WA) and South Australia (SA)

MEU, metabolisable energy utilised; MEP, metabolisable energy produced by the grazing animal per unit area; DSE, dry sheep equivalents; n.a., not available Project and site no. Location Dominant pasture species Mean annual rainfall

Stock class Stocking rate (DSE/ha) Liveweight gain (g/day) MEU-derived grazing days Proportion utilised (kg utilised/ MEP-derived grazing days (DSE/ha) (mm) (DSE/ha) kg produced)

03–42, site 1 Quairading, WA Perennial grass 350 Merino mixed 10 67 410 0.14 3023 03–42, site 2 Quairading, WA Perennial grass 350 Merino mixed 9 104 442 0.12 3685

03–30 Pingrup, WA Lucerne 380 Merino mixed 1 314 41 n.a. n.a.

03–50 Broomehill, WA Perennial grass 450 Merino ewes 31 –1 983 0.49 1994

03–67 Tambellup, WA Perennial grass 425 Merino wethers 41 –66 3598 0.70 5145

03–47 Pingrup, WA Atriplexspp. 380 Merino wethers 13 –95 459 0.69 661

02–03, site 1 Jacup, WA Perennial grass 410 Merino wethers 9 69 534 0.12 4561

02–03, site 2 Jacup, WA Perennial grass 410 Merino wethers 15 18 426 0.39 1094

6, 2 Kangaroo Island, SA Perennial grass 550 Merino wethers 7 13 2603 0.36 7270

6, 3 Kangaroo Island, SA Perennial grass 550 Merino wethers 6 –3 1954 0.38 5091

03–23 Trayning, WA Atriplexspp. 320 Angus steers 7 431 n.a. n.a. n.a.

Table 1. Metabolisable energy (ME) utilisation and ME-adjusted dry sheep equivalent (DSE) predicted for sheep of varying liveweight and weight gain using Eqns 1–4

Bodyweight Liveweight change (kg/day)

(kg) –0.2 –0.15 –0.1 –0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 ME requirements (MJ/day) 30 0.4 1.8 3.2 4.5 5.9 8.5 11.0 13.6 16.2 18.7 21.3 40 1.1 2.7 4.3 5.8 7.4 10.4 13.3 16.2 19.2 22.1 25.0 50 2.3 4.0 5.6 7.3 8.9 12.0 15.1 18.1 21.2 24.3 27.4 60 3.7 5.4 7.1 8.7 10.4 13.5 16.7 19.8 22.9 26.0 29.1 70 5.2 6.9 8.6 10.2 11.9 15.1 18.2 21.3 24.5 27.6 30.7

ME-adjusted DSE grazing days

30 0.0 0.2 0.4 0.5 0.7 1.0 1.2 1.5 1.8 2.1 2.4

40 0.1 0.3 0.5 0.7 0.8 1.2 1.5 1.8 2.2 2.5 2.8

50 0.3 0.4 0.6 0.8 1.0 1.3 1.7 2.0 2.4 2.7 3.1

60 0.4 0.6 0.8 1.0 1.2 1.5 1.9 2.2 2.6 2.9 3.3

prominently in the less saline revegetated sites, with Atriplex

spp. established on the saltier sites and some M. sativa and

C. gayana on the less saline, well drained sites. Feed on offer was not significantly correlated with site characteristics by multiple linear regression analysis (P > 0.05). There was a quadratic relationship between ECe and MEP-derived grazing days [polynomial (quadratic) regression; MEP =

–0.0026(ECe)2 + 6.44(ECe) + 2490; R2 = 0.62, P = 0.024; Fig. 1]. MEP was not correlated with summer rain (P>0.05).

Stocking rates ranged from 1 to 41 DSE/ha and mean liveweight change of sheep varied from–95 to 314 g/day. The estimated proportion of pasture utilised varied from 12 to 70%. MEP-derived grazing days varied from 661 to 7270 across the sites (Table 2). The grazing value of the most productive site was estimated to be AU$360/ha using a comparative ME value achieved by providing lupins as a supplementary feed.

Discussion

The potential to create a valuable source of livestock feed was demonstrated across the sites with total grazing days on the sites ranging from 660 to more than 7200 DSE/ha. In the case of the most productive saltland, carrying capacity would be at least as high as adjacent unaffected land. The ability to graze saltland pastures during the seasonal period of feed shortage (~February–June) increases the value of these pasture systems because it reduces the cost of providing supplementary feeds to livestock. Correspondingly, the saltland pastures were reserved for feeding higher value classes of livestock (e.g. weaner lambs) during the autumn period. Although we established a significant correlation between ECe and livestock productivity, the complexity of these systems and the difficulty in collecting enough data to test this hypothesis necessitates that the results be considered cautiously.

To adequately test our hypothesis, site characteristics that contribute to the capability of saline land for livestock production require further investigation on a broader scale. The analyses in this study showed that the relationship between site characteristics and forage production may be non-linear (Fig. 1), and this relationship needs to be appropriately defined. This paper demonstrated the use of ME production to assess animal production capability, but further refinement of this method and equations using a large dataset may be necessary. Soil physical properties were not included in the present regression analysis due to a lack of detailed information. However, soil texture, sodicity, hypoxia (or anoxia) and surface drainage would also affect the productivity of sites. Nicholset al. (2008a, 2008b) demonstrated that both salinity and waterlogging impacted on the growth of a large range of pasture plants and some species were more tolerant of either stress than others. It is likely that the inverted quadratic relationship between MEP and soil ECe reflects the interaction between soil salinity and other factors that influence plant growth. For example, if water availability is limiting the growth of perennial plants in summer and autumn, then an increase in soil moisture (associated with shallow water tables) will boost growth until salinity, sodicity or hypoxia becomes a greater limitation to growth. Adverse salinity and waterlogging interactions have been documented for crops and woody perennials (Barrett-Lennard 2003). The ability of some plant species to better manage these interactions would be a further source of variation in the relationship between MEP and soil ECe and would shift the inflection point of the quadratic curve. There was no correlation between MEP and rain, indicating that rain may not have varied enough among the sites to cause a significant limitation to plant growth over the period of the study. Alternatively, the relationship may have been confounded by variation in species composition at the sites, some species may be more responsive to rainfall than others. A strong positive relationship between precipitation events and the growth of perennial grasses was demonstrated by Cable (1975), but relationships between growth and summer precipitation events are not available for many saltland pasture species.

Grazing pressure will typically differ between farms because drivers of grazing timing and duration and livestock class vary among production systems. In this study, grazing intensity was related to livestock class, protection of plants from overgrazing or grazing too early, livestock growth targets and demand for feed (related to the cost and abundance of alternative feed sources). Differences in grazing intensity among the sites made comparisons of livestock production capability difficult and as a result we estimated ME production using livestock data. In another study, grazing days was determined to be double in saltbush plots stocked at 30 sheep/ha, compared with a similar plot stocked at 15 sheep/ha (Morcombe et al. 1996), which is likely to be a result of differences in grazing intensity and subsequent pasture utilisation. If not considered, higher grazing intensity will result in higher feed utilisation and apparent higher site productivity in terms of MEP. The method to adjust for grazing intensity reported in this paper allows comparisons of MEP to be made between sites of differing grazing intensity.

The unique characteristics of salt accumulating shrubs can provide additional nutritional challenges and benefits to livestock 0 1000 2000 3000 4000 5000 6000 7000 8000 1000 2000 3000 Soil ECe (mS/m)

MEP derived grazing days (DSE/ha)

Fig. 1. Relationship between the electrical conductivity of saturated soil extract (ECe) in the topsoil and grazing days derived from estimated metabolisable energy produced (MEP).

production. In saltbush dominant pastures, animal growth may be restricted unless a low-salt supplementary feed is available (Franklin-McEvoyet al. 2007; Normanet al. 2008). However, across the sites in this study, low-salt pasture species and/or supplements were readily available and a high intake of saltbush was unlikely to have been problematic. Sodium and potassium are essential macronutrients and livestock would probably have gained a nutritional benefit from high levels of these in saltbush. High crude protein and sulfur levels in saltbush may be another benefit of including saltbush as part of a mixed diet (Normanet al. 2004). Additionally, there are potential benefits from high levels of vitamin E in saltbush (Pearceet al. 2005) and improved efficiency of wool growth from high-salt diets (Thomas

et al. 2007a). The value of benefits of Atriplex spp. in grazing systems, additional to ME, should be considered in future studies.

Acknowledgments

The generous collaboration and input into the sites by the host farmers is gratefully acknowledged. Thank you Ted, Jenny and Tony Altham, Deane and Sarah Aynsley, Craig Bignell, Terry and Linda Lee, Bart Hulls, Dean Hull, John Pepall and Malcolm Schaefer. We would also like to thank Linda Vernon, Trayning CLC for her support in this project. This work was supported by funds from the Land, Water and Wool Program, through the SGSL subprogram.

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Manuscript received 30 April 2008, accepted 21 October 2008