An on-farm evaluation of the capability of saline la by pharmphresh34


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

D Thomas1, C White1, J Hardy2, J-P Collins3, A Ryder2, J McFarlane4
  CSIRO Livestock Industries, Floreat, Western Australia
  Department of Agriculture and Food Western Australia, Albany, Western Australia
  Department of Agriculture and Food Western Australia, Katanning, Western Australia
  Rural Solutions SA, Struan, South Australia
Future Farm Industries CRC, The University of Western Australia, Crawley, Western Australia

Land salinisation reduces vegetation growth through a range of mechanisms involving
nutrient toxicity and deficiency (Barrett-Lennard 2003). The nutritive value of vegetation may
also be lower because the diversity of forage species that will grow on saline land is reduced.
In addition, adaptive mechanisms of plants growing in saline environments, for example salt
accumulation, may create a nutritionally imbalanced feed for livestock (Masters et al. 2007).
However, productivity on saline sites may be increased by the introduction of productive,
salt-tolerant plant species that use soil water available in salt affected areas. The capability of
salt-affected land for animal production can be quantified in terms of the metabolisable
energy produced (MEP) per unit area, that can be eaten by the grazing animal (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 low productivity in saltland pastures is related to a wide range of site characteristics
including soil type, soil salinity, 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 utilized (MEU, MJ/ha) was determined and an adjustment
for grazing intensity is applied to calculate MEP. We hypothesised that forage biomass,
nutritive value and MEP would be related to the site characteristics that we measured.
Materials and methods
Sites and locations
Eight existing saltland pasture sites were included in the study. These were selected from a
large network of farms across southern Australia that established saltland pastures through the
Sustainable Grazing of Saline Land (SGSL) project. Sites were selected on the basis that
grazing and site characterisation data could be obtained and used to determine relationships
between forage biomass, feeding value and metabolisable energy produced. Site
characteristics recorded were location, climate, rain, land area, soil characteristics, 2 measures
of soil salinity; electrical conductivity of soil saturation extract (ECe) (derived from electrical
conductivity of the 1:5 soil extract (EC1:5) in the top 20 cm) andapparent electrical
conductivity of the soil (ECa) (derived from EM38 electromagnetic induction mapping),
pasture establishment methods and species, feed on offer (FOO) periods of grazing, stocking
rates, reasons for start and end points for grazing, and animal liveweight before and after
grazing were recorded at each site.
Forage species
The SGSL project established combinations of salt-tolerant forage species on the eight
demonstration sites between 2002 and 2004. The introduced forage species included perennial
grasses; Chloris gayana Kunth cvs Callide, Kantambora, Finecut and Topcut, Festuca
arundinacea Schreb. Cv Advance, Panicum coloratum L. (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 cvs
Tyrrel and Dundas and Puccinellia ciliate Bor), legumes (Medicago sativa L. cv Sequel,
Trifolium michelianum Savi cv. Frontier), saltbushes (Atriplex amnicola Paul G Wilson, A.
nummularia L., 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 shrubs were established as seedlings, sown using a
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Salinity, water and society–global issues, local action
commercial tree planter (e.g. Ezy Planter 2000, Chatfield Enterprises, Australia). The species
sown differed among the sites. 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.
Metabolisable energy
Animal liveweight and weight change were used to calculate grazing MEU on the sites over
the grazing duration (White et al. 2007). MEP was calculated from an equation derived from
a Grassgro™ simulation which provides an estimate of a standard feeding value for the
pasture. The model assumes ME utilisation is similar in saline compared to non-saline pasture
MEP = MEU (0.513 – 0.735/s - 4.084w - 0.923/s2 – 15.011w2 + 8.013w/s + 1.264/s3 –
38.203w3 +14.484w2/s – 5.219w/s2)
Where; s = stocking rate (DSE/ha), w = liveweight gain (g/d)
Statistical analysis
Multiple linear regression analysis was used to determine correlations between metabolisable
energy produced (response variate) and site characteristics. Simple linear regression analysis
was used to determine individual correlations. All analyses were conducted using the
GenStat® statistical package (Genstat 2003).
Mean site EC1:5 in the topsoil ranged from 10 to 363 mS/m and ECa ranged from 31 to 126
mS/m. Water table level across the sites ranged from -0.2 to 3.8 m below the surface and
ground water EC ranged from 1400 to 6000 mS/m. FOO produced ranged from 699 kg/ha on
a M. sativa -sown plot to 9037 kg/ha on a F. arundinacea and T. ponticum dominant plot. P.
ciliate and T. ponticum featured 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 to site characteristics by multiple linear
regression analysis (P>0.05). There was a weak negative trend between EC1:5 and MEP
derived grazing days (R2=0.33, P=0.14; Figure 1).

Figure 1 Relationship between electrical conductivity (ECe) in the top-soil and grazing days
         derived from estimated metabolisable energy produced (MEP).
Stocking rates ranged from 1 to 41 DSE/ha and mean liveweight gain of sheep varied from -
95 to 314 g/d. The estimated proportion of pasture utilised varied from 0 to 69%. MEP
derived grazing days varied from 694 to 5229 across the sites (Table 1). The grazing value of
the most productive site was estimated to be $480/ha using a comparative energy value
achieved by providing lupins ($200/tonne, 13.3 MJ/kg) as a supplementary feed.

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Salinity, water and society–global issues, local action
Table 1 Livestock class, stocking rate, liveweight gain and MEU and MEP derived grazing days
        of producer network saltland demonstration sites

Several classes of livestock were grazed on the sites, although predominantly 6 month to 2
year old Merino sheep. All sites were grazed during the autumn to early winter period. The
decision to destock plots depended on the age of sheep, weaner sheep tended to be removed
as soon as they started losing weight, while older sheep were taken off the plots after the no
feed of value remained, as determined by visual assessment. De-stocking plots was partly
influenced by perceived sensitivity of some species to permanent damage from grazing
(usually in recently established plots, or those containing small shrubs). Grazing intensity
varied widely among sites 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.
The potential to create a valuable source of livestock feed was demonstrated across the sites
with total grazing days on the sites ranging from about 700 to more than 5000 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 (autumn feed gap) considerably increases the value of these pasture systems, which
was highlighted by the farmers’ consistent use of these pastures for feeding higher value
classes of livestock (e.g. weaner lambs) during the autumn period. We were unable to
establish significant correlations between saline site characteristics to livestock productivity,
which partly reflects the complexity of these systems and the difficulty in collecting data. To
adequately test our hypothesis, site characteristics that contribute to the capability of saline
land for livestock production will require more sites and probably other measures of site
characteristics. This paper demonstrated the use of metabolisable energy production to assess
animal production capability, but further refinement of this method and equations will
probably be necessary. Soil physical properties were not included in the current regression
analysis and soil texture would probably be important.
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 an adjustment was necessary. In another study, grazing
days was determined to be double in saltbush plots stocked at 30 sheep/ha, compared to a
comparable plot stocked at 15 sheep/ha (Morecombe et al. 1994), 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 apparently higher MEP.
The unique characteristics of Atriplex spp. shrubs can provide additional nutritional
challenges and benefits to livestock production. In saltbush dominant pastures, feed intake
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Salinity, water and society–global issues, local action
may be restricted by the high salt content of the forage. 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 a problem.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 (Norman et al. 2002). Additionally, there
are potential benefits from high levels of vitamin E in saltbush (Pearce et al. 2005) and
improved efficiency of wool growth from high-salt diets (Thomas et al. 2007). These
additional benefits of incorporating Atriplex spp. in grazing systems should be considered in
future studies.
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 & Wool Program, through the
Sustainable Grazing on Saline Lands (SGSL) Subprogram.
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      production. Agriculture, Ecosystems and Environment 119, 234-248.
Morecombe PW, Young GE, Boase KA (1994) Short term, high density grazing of a saltbush
      plantation reduced wool staple strength in Merino wethers. Animal Production in
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Norman HC, Dynes RA, Masters DG (2002) Nutritive value of plants growing on saline land.
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      Saline Lands (PUR$L)'. Perth.
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      tocopherol concentrations and meat colour stability in sheep grazing saltbush (Atriplex
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      wool growth but decreases feed digestibility in sheep across a range of diets. Australian
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