Sidebar: How to tell when salt is really hurting your fields

Tuesday, August 4, 2009

What are the warning signs that salt contamination might be at work?
Keith Reid, the Ontario agriculture ministry's soil fertility specialist, says the sodium portion of salt can stick to clay and therefore can build in soil and hurt its structure. An indication of buildup would be the soil falling apart and turning to mud when it rains, making it susceptible to crusting.

High concentrations of salts will reduce a plant's growth because they affect the process it uses to draw water and nutrients. "In serious situations, you'll get roots that actually look like they're burned. They'll be darkened and look like somebody has held a lit match to them," he says.

The same sort of effect is found when too high a rate of fertilizer is applied too close to seeds. In severe situations, there will be no growth.

Agronomist Owen Gifford explains that when soil's salt level is too high, roots can't draw water and nutrients. "Even when the soil seems wet enough, the plants are wilting and dying from dehydration," he says.

Reid recommends testing a soil sample for conductivity to determine the total salts. "Conductivity is the test that tells you whether it really is a salt problem," he says, pointing out that low pH "can look an awful lot like a salt injury in the field."

A sodium soil test will determine whether there are structural problems in the soil and provide pointers to the source of contamination: "If it is high sodium, we don't normally apply sodium as a fertilizer, so it's coming from somewhere else."

The only way to get rid of the contamination is to flush it out, say both Gifford and Reid. That means being able to get water into the soil and having a way to drain it, such as tiles.

Reid says salt will eventually leach out, but that could take one or two growing seasons, depending on soil structure. But gypsum would be needed in areas showing high concentrations of the sodium portion of the salt. The material displaces sodium in the soil structure so it can be flushed away.

Time won't help if the situation causing the contamination isn't addressed, he adds.