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UNIT 7

Saltland Toolbox

 

7.6  Definitions

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Alluvial
– Describes material deposited by, or in transit in flowing water.
 
Aquifer – A saturated geological material, that when drilled, can yield a useable quantity of groundwater. In the context of salinity, we often think of aquifers as being the material through which water moves in its path from recharge areas to discharge areas.

Baseflow – The water in a stream that results from groundwater discharge to the stream. This discharge often maintains flows during seasonal dry periods and has important ecological functions.

Capability (of saltland) – The inherent potential of saltland to be productive and profitable. This is determined by a number of factors (relating to soils, landscape, climate), but in particular relating to the decline in productive potential associated with increasing salinity and waterlogging. It can be quantified in DSE/ha for grazing land. Pasture options for optimizing productivity will vary as saltland capability varies (eg due to salinity & waterlogging conditions).

Catchment – An area of land that drains surface water to a common outlet. A catchment is usually made up of many sub-catchments of the tributary streams to that river.

CRC Salinity – Cooperative Research Centre for Plant-based Management of Dryland Salinity. This CRC operated between July 2000 and June 2007, and was a partner in the Sustainable Grazing on Saline Lands (SGSL) Initiative.

CRC Future Farm Industries – Cooperative Research Centre for Future Farm Industries. This CRC succeeded the CRC Salinity, and is conducting current research in ‘Farming Saline Landscapes’.

Discharge – Outflow of groundwater as seepage from transverse flow, or as capillary rise from shallow watertables. This often produces the symptoms of dryland salinity (ie bare ground, salt crusts, waterlogging and/or changes in vegetation).

DM – Dry matter, a measure of pasture productivity (eg kg DM/ha).

DSE – Dry sheep equivalent, a standard unit frequently used to compare the feed requirements of different classes of stock. By definition, a 50 kg wether maintaining a constant weight has a DSE rating of 1 (and an energy requirement of 8.5 to 9MJ/day).

DWLBC – Department of Water, Land and Biodiversity Conservation.

EC, ECe, EC 1:5, ECa – EC is an abbreviation for electrical conductivity. The individual units have been defined in Section 7.2 – measuring salinity and waterlogging.

Electromagnetic (EM) surveys – The detection and mapping of variability in sub-surface conductivity (spatially and with depth) through the application of electromagnetic fields. The variability measured can be caused by the presence of salt, moisture, clay materials and conductive minerals. Ground-truthing (through soil sampling) is required to correlate EM survey data to attributes such as soil salinity. Survey systems vary in complexity from hand-held meters to GPS-equipped, data-logging quad-bike systems and even airborne systems for larger-scale deeper (regional) surveys.

Groundwater – Underground water contained in a saturated zone of soil or geological strata.
 
Groundwater Flow System (GFS) – Different types of GFS characterise the scale of a groundwater system and are determined by the relief of the landscape and topographic position in a regional context. Aside from the scale of groundwater flow paths, the term GFS also encompasses notions of a range of hydrogeological attributes which help to describe groundwater system behaviour (eg. magnitude and delays in groundwater response to significant rainfall events or land use change). Three broad classes of GFS are recognised:

  • Local systems – occur in small sub-catchments in hilly areas. Flow paths between recharge and discharge areas are less than 5 km. Groundwater flow patterns correlate well with surface topography. These systems are the most responsive to recharge reduction strategies.
     
  • Intermediate systems – occur in larger catchments with flat plateau or alluvial valley fills. Flow paths are in the range 5-50 km.
     
  • Regional systems – occur in large sedimentary basins / broad riverine plains and have large horizontal flow scales, greater than 50 km. These larger systems can be sluggish in nature, taking longer to show signs of salinity, or can be very responsive if geological materials are highly transmissive (eg limestone aquifers). Depending on geology, they can be the least responsive to management changes. If engineering solutions (eg drainage, groundwater pumping) are not possible, the use of saltland pasture is critical in the productive use of this kind of landscape.


Inundation
– Flooding of the land surface and plants by excess surface water.

Recharge – Unused rainwater, or surface water inflows, which percolate down through the soil profile below root zones to the watertable, which causes watertables to rise.
 
Salinity – Salinity refers to the presence of dissolved salts in soil and water. Salinity can be natural (‘primary’ salinity) or caused by land management practices (‘secondary’ salinity). In naturally saline areas, the plants and animals have evolved to cope with these conditions. In contrast, in areas of secondary (human-induced) salinity, a build up of salt can adversely impact on water, soil, vegetation or agricultural production. Salinity can occur with or without a watertable influence.
 
Salinity units and measurement – The simplest measurement of salinity is to determine the electrical conductivity (EC) of a water sample. That is, how easily a solution will pass an electric current.

SARDI – South Australian Research and Development Institute (see ‘Contacts & websites’).

SGSL‘Sustainable Grazing on Saline Lands’ Initiative.

Sodic soil – A soil with a relatively high proportion of exchangeable sodium on the clay particles. This can cause soil structural problems. Saline conditions alleviate sodicity issues in soil, but when rain leaches out salts (freshening the soil water) this can cause clay particles to de-aggregate and disperse. The dispersed clay particles move through the soil clogging pores and reducing infiltration and drainage. On drying they can form a hard-setting layer. At an exchangeable sodium percentage (ESP) of 6 soils are deemed sodic, and in most cases will disperse at this and higher ESP values. Dispersion increases with increasing ESP and pH. Applying gypsum to alkaline soils (and/or lime to acid soils or soils affected by acid sulphate) may help to displace the sodium, and improve soil structure.
 
Soil structure – The way in which soil particles aggregate or group together. Well structured soils are those with higher clay and organic matter contents in which the particles are held together as friable aggregates, crumbs or peds. Pure sands do not have this capacity and are said to have an ‘apedal’ structure.

Soil texture – is determined by the relative amounts of sand, silt and clay in a soil. Texture strongly influences soil properties such as structure, water infiltration, moisture and nutrient retention, plant available water, trafficability and ease of tillage. Clays have a greater ability to absorb water than sands, therefore the conversion factor used to estimate ECe values from EC1:5 values will depend on soil texture.

Stolon – a prostrate stem, at or just below the surface of the ground that produces new plants from buds at its tips or nodes.

Surface water – Water in streams, creeks, rivers, lakes, dams, reservoirs and other surface water bodies.

Topography – Relief and form of a land surface.

Waterlogging – a soil is waterlogged if any part of the plant root zone is saturated with water. High waterlogging occurs when the soil is saturated to within 10 cm of the soil surface over the winter. Indicators of waterlogging include a shallow watertable, continued wetness of the soil surface, presence of weeds such as rushes (Juncus spp.), water buttons (Cotula spp.), sea barleygrass and/or puccinellia; patchy or stunted crop and pasture growth; yellowing or reddening of leaves; excessive growth of algae; “rotten egg gas” smell from soil (a sign of anaerobic conditions); presence of dull yellow mottles (minor waterlogging) or blue-grey mottles (strong waterlogging) in the soil profile.

Watertable – Is the presence of water in near surface soils at saturated levels. The watertable level is the surface in an unconfined aquifer where the water in the soil pores is held at atmospheric pressure – above the watertable, the water in soil pores is held at pressures above atmospheric. It is the height to which the water level will rise in a well drilled into an unconfined aquifer.

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