Dryland salinity is a natural process for

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

, just like other processes such as

wind erosion Aeolian processes, also spelled eolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit material ...

. Salinity degrades land by an increase in soil salt concentration in the environment, watercourse or soil in unirrigated landscapes, being in excess of normal soil salt concentrations in dryland regions.

Overview

Salinity refers to the movement and concentration of

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

in the

landscape A landscape is the visible features of an area of land, its landforms, and how they integrate with natural or human-made features, often considered in terms of their aesthetic appeal.''New Oxford American Dictionary''. A landscape includes th ...

and its associated detriment to land and

water resources Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. These resources can be either Fresh water, freshwater from natural sources, or water produ ...

;

dryland Drylands are defined by a scarcity of water. Drylands are zones where precipitation is balanced by evaporation from surfaces and by transpiration by plants (evapotranspiration). The United Nations Environment Program defines drylands as tropical ...

salinity refers to salinity in unirrigated landscapes. Salinity processes extend from local to regional scales and are driven by imbalances in the water budget that result, primarily, from agriculturally driven landscape change. There are two types of salinity:

Types of salinity

There are two types of salinity. Primary salinity (natural salinity) and secondary salinity (induced salinity). (Nrm.qld.gov.au, 2013) Primary salinity naturally occurs in arid and saline environments such as salt lakes, marshes, pans and salt flats. Natural accumulation of salt in soils is an outcome from previous cycles of drainage, desiccation and sea winds. High levels of salt are often found in dry soils, more so than wet soils as it is diluted and washed through the

soil profile A soil horizon is a layer parallel to the soil surface whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. ...

. (Barry and Holwell et al., 2012). Secondary salinity is a direct result of human interaction with the land, during

development Development or developing may refer to: Arts *Development (music), the process by which thematic material is reshaped * Photographic development *Filmmaking, development phase, including finance and budgeting * Development hell, when a proje ...

agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...

and irrigation. Certain land practices have led to changes in the natural structure of the

biosphere The biosphere (), also called the ecosphere (), is the worldwide sum of all ecosystems. It can also be termed the zone of life on the Earth. The biosphere (which is technically a spherical shell) is virtually a closed system with regard to mat ...

resulting in excess salting of the land, waterways and soils; thus having detrimental effects on biodiversity and the lands'

productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proce ...

Salinity and water cycle

Factors such as

climate Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...

, features of landscape, soils,

drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root gro ...

, aspect and the effects of human activities; all impact on the severity and occurrence of dryland salinity. Dryland salinity effects human and natural resources, such as native vegetation and crops, animals, infrastructure, agricultural inputs, biodiversity, aquatic ecosystems and water supply quality in the environment. Understanding dryland salinity requires a look at the

water cycle The water cycle (or hydrologic cycle or hydrological cycle) is a biogeochemical cycle that involves the continuous movement of water on, above and below the surface of the Earth across different reservoirs. The mass of water on Earth remains fai ...

. Water enters the soil from precipitation – this is called Infiltration; water may remain indefinitely within the spaces or pores between soil particles as soil moisture. Soil moisture may be lost to the surface or atmosphere directly, or through plant uptake – this is called evapotranspiration.

Soil moisture Soil moisture is the water content of the soil. It can be expressed in terms of volume or weight. Soil moisture measurement can be based on ''in situ'' probes (e.g., capacitance probes, neutron probes) or remote sensing methods. Water that enters ...

may also continue to move downward to join the groundwater—this is called

groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in ...

. Recharge is most likely to occur when the amount of water that is available to the soil exceeds the soil’s capacity to store it (field capacity). Recharge may also occur by saturated flow when water bypasses the soil matrix as it moves to depth in macropores (e.g. root holes, fractures). Excessive recharge may raise the water table locally, or at a landscape scale. When brackish to saline groundwater intersects the ground surface and discharges, this is termed saline discharge. Areas of discharge are called saline seeps (when groundwater intersects the soil surface) or saline scalds (where water is lost by evaporation only). Groundwater discharge manifests in such problems as: reduced agricultural production, degradation of natural environment, reduced surface water quality, damage to infrastructure including roads, as well as

soil erosion Soil erosion is the denudation or wearing away of the Topsoil, upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, Atmosphere of Ea ...

and denudation of land.

Reasons for dryland salinity

Dryland salinity is broadly the result of three processes:

Groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in ...

, Groundwater movement and

Groundwater discharge Groundwater discharge is the volumetric flow rate of groundwater through an aquifer. Total groundwater discharge, as reported through a specified area, is similarly expressed as: :Q = \fracKA where :''Q'' is the total groundwater discharge ( 3·T� ...

. (Environment.nsw.gov.au, 2013) Groundwater recharge occurs naturally, being a key process in the development of salinity, however land clearing accelerates this development as the once present deep-rooted plants do not use excess runoff, and it now seeps past the root zone to enter the groundwater system. (Environment.nsw.gov.au, 2013)

Evapotranspiration Evapotranspiration (ET) refers to the combined processes which move water from the Earth's surface (open water and ice surfaces, bare soil and vegetation) into the Atmosphere of Earth, atmosphere. It covers both water evaporation (movement of w ...

is reduced, as vegetation is lost, resulting in an imbalance in groundwater recharge and discharge, causing the water table to rise.

Capillary action Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of external forces like Gravitation, gravity. The effe ...

brings salt to the surface initiating surface salt accumulation. (Barry and Holwell et al., 2012) Prevention and alleviation of dry land salinity is a simplistic concept in theory however complex in application. Ceasing the removal of deeply rooted vegetation in order to moderate unbalanced groundwater recharge and the replanting of deeply rooted vegetation such as Eucalyptus and salt tolerant species in regions where salinity is present, will start to alleviate the salt and ground water discharge problems. (Barry and Holwell et al., 2012) However establishing plants in salt laden areas is extremely difficult. Dryland salinity is a sign that the water balance of the nearby area of land or

catchment A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, th ...

has been altered. Clearing as little as 25% of a catchment can cause salinity to occur. In addition to adding extra recharge, salinity may also be caused if the aquifers discharge capacity has been exceeded. In many Australian landscapes, aquifer capacity may be several orders of magnitude below that of the altered recharge. Restoring the balance requires either the introduction of natural vegetation (e.g. mallee eucalyptus or perennial grasses), which intercepts and transpires most of the incoming rainfall; or by adapting agriculture to the increased area of shallow, saline groundwater.

Management

Role of soils

Dryland salinity management often focuses on

vegetation Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...

, yet it is the collective role of

s and vegetation that has an effect on the root cause of the problem, recharge.

Soil health Soil health is a state of a soil meeting its range of ecosystem functions as appropriate to its environment. In more colloquial terms, the health of soil arises from favorable interactions of all soil components (living and non-living) that belong ...

cannot be ignored as a valuable and extensive activity for the management of dryland salinity – the multiple benefits of improving soil health are clear and can be motivated by the potential for local and regional economic and social gains. Soil is considered in two contexts when it comes to dryland salinity: Recharge and discharge. ;Soils in groundwater recharge areas Soils absorb and store water according to their water holding or

field capacity Field capacity is the amount of soil moisture or water content held in the soil after excess water has drained away and the rate of downward movement has decreased. This usually occurs two to three days after rain or irrigation in pervious soils of ...

and how dry they are to start with. In much of Victoria, under typical rainfall and natural vegetation cover, soils take on water during wet winters and dry out over summers as plants consume the water (Young & Young, 2001). The drier the soil when leading into winter, the more water can be stored that might otherwise leak to groundwater. To reduce recharge to levels that existed in pre-clearing conditions is generally infeasible in most agricultural landscapes. This is because there are too few profitable perennials that can replace crops or that can be adopted at the scale required. In most recharge areas that are at risk of future salinity, the goal is to minimise recharge. This can be done by planting wide-spaced trees (alley farming), areas of perennials on suitable soils, and by preventing soils from being left without a significant leaf area in winter and spring. In recharge areas remote from saline areas there is often little incentive for farmers to adopt low profit, low recharge systems. In addition, recharge is the source of fresh groundwater, and a trade off between consumptive use and salinity should be acknowledged. ;Soils in groundwater discharge areas The manifestation of dryland salinity is largely a problem of groundwater – however the accumulation of salt within the soil and at the surface due to proximity to or saturation by saline groundwater causes changes to the soil’s chemistry, structure and stability, and the plant life that it supports. ;Managing soils for dryland salinity in catchments In discharge areas, salinity can be managed by establishing salt-tolerant plants or by engineering systems. Engineering systems include deep open drains, pumps, siphons and various forms of surface water management. Engineering system involve the obvious discharge of salt and water. While saline areas also discharge salt and water, the abundance and timing will be changed. In most Australian states, farmers would be advised to seek advice before using engineering systems. Establishing salt-tolerant plants can improve salt discharge rates and improve soil health. Improvements undertaken at a

scale bring many benefits, not the least of which is providing for increased agricultural and associated regional productivity – using water for production that otherwise would contribute to an environmental problem.{{cn, date=May 2016

References

Department of Primary Industries (DPI)
viewed June 2007. *Young, A & Young R 2001, Soils in the Australian landscape,

Oxford University Press Oxford University Press (OUP) is the publishing house of the University of Oxford. It is the largest university press in the world. Its first book was printed in Oxford in 1478, with the Press officially granted the legal right to print books ...

Melbourne Melbourne ( , ; Boonwurrung language, Boonwurrung/ or ) is the List of Australian capital cities, capital and List of cities in Australia by population, most populous city of the States and territories of Australia, Australian state of Victori ...

.
Dryland salinity – causes and impacts
ccessed: 20 Oct 2013
Dryland Salinity
ccessed: 15 Oct 2013
Types of salinity
ccessed: 15 Oct 2013
Factors contributing to salinity
ccessed: 20 Oct 2013 Soil science Natural resources Land management