Controlling salinity with irrigation
Irrigation can help control saline soil and the industry is managing the environmental hazard of salinity by using new techniques and new knowledge, says Jim Miller, soil and water specialist at the Agriculture Canada research station in Lethbridge. He points to two general salinity-fighting strategies irrigation offers.
Good drainage is the chief bulwark against soil salinity. But improving drainage with structural controls, such as underground weeping tile, is very expensive on a farm scale. “The high value of irrigated land, and the fact that irrigation farms are relatively compact, makes it economically feasible to fight salinity by improving drainage,” he said.
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Using water to flush salts down is another way to fight salinity with irrigation. “Precise water application with fall irrigation allows farmers to flush salts down below the root zone, yet not so low the salts enter the groundwater.”
The strategy is helped by these factors:
- Water quality. Surface runoff is the chief source of irrigation water used in southern Alberta, and that means it is relatively salt-free. Some areas, such as the U.S. sun belt states of California and Arizona, amplify salinity by irrigating with saline groundwater.
- Application methods. The dominance of sprinkler systems, as opposed to ditch irrigation, also helps reduce salinity problems in southern Alberta.
“Sprinklers allow more precise control over the amount of water applied and do a much better job of application,” said Miller. “Ditch systems tend to only wet the surface soil and aggravate salinity.”
- Underlying drainage. The layer of unsorted clay, sand, gravel and boulders in the glacial till underlying southern Alberta’s soils allows superior natural drainage because of good permeability. “In fact, recent geological evidence of large cracks, or ‘macropores’ in the surface of this glacial till shows it may be even more permeable than previously thought,” said Miller. “This extra drainage capacity expands an irrigator’s opportunities to use water management for salinity control.”
Canals that leak are also being scrutinized by irrigators in southern Alberta. They are being lined with impermeable membranes where necessary. Some water is being routed through buried pipelines, and interceptor drains are being built to re-route heavy seepage back into the system.
– Alberta Irrigation Projects Association
Earthworms: nature’s plow
Tillage has been described as a mechanical substitute for the burrowing activities of earthworms and other soil animals. As earthworms plow through the soil, they create a network of channels within the rooting zone. In doing so, they improve the gas exchange and structure of the soil.
This can increase water infiltration rates by two to 10 times that of similar soils which lack earthworms. The channels that earthworms create act as pathways for roots, allowing roots to move easily through the soil. Introducing earthworms in compacted soils has increased the rate of seed germination, heading and grain yield of barley and wheat.
Earthworms prefer to eat dead and decaying plants that are often colonized by bacteria and fungi, some of which can cause crop diseases. In Australia, earthworms have been linked to reduced crop losses from a fungal root disease.
Scientists at the Agriculture Canada research centre in Lethbridge are studying earthworms and how they are affected by tillage and cropping practices.
In our long-term tillage plots, we have consistently found more earthworms under zero tillage than under conventional tillage.
By encouraging earthworm populations, we may be able to reduce problems with crop residue management under zero tillage. Earthworms speed decomposition of organic matter and the cycling of soil nutrients. The cycling of nitrogen increases as much as three times in soil with earthworms. Leaving residues on the soil surface, provides a stable habitat and a continuous food supply for these moisture, temperature and light sensitive soil animals.
In learning more about earthworms under agricultural and climatic conditions, scientists will be better able to develop soil management practices that use the plowing abilities of these soil animals to improve soil quality.
– Agriculture Canada
