Pulse crops are playing an important role in building soil quality, especially when they’re combined with a host of soil-friendly farming techniques.
That’s the finding of a 12-year study by researchers at Agriculture and Agri-Food Canada’s Lethbridge Research Centre, led by soil scientist Frank Larney.
In the study, published in Agronomy Journal, Larney and company wrote that the crops fix nitrogen through a symbiotic relationship with soil microbes — in this case bacteria — that live in their roots. The bacteria pull nitrogen from the atmosphere and then convert it to a plant-available form that’s readily available during the growing season.
When the plants are harvested and the root system dies, the roots slowly decay, releasing the remaining nitrogen for the use of future crops. This sort of soil-building activity is very important, Larney said.
“Soil is a limited resource, and we need to be improving our soil quality, or at least maintaining it, in order to keep growing food,” said Larney.
Larney and his team went beyond this however, and examined a conservation package that included reducedtillage, narrow-row cultivation, cover crops, and manure compost to protect and bolster the soil. They avoided tillage as much as possible to avoid open soil.
“You don’t want to have a bare soil situation because you’re losing moisture, which is very valuable in a semi-arid area for growing crops. And you’re also exposing that surface soil to wind and water erosion,” said Larney.
Farmers can also plant dry beans in narrow rows to increase soil protection. Farmers usually plant beans in wide rows, and cultivate between the rows, which works up the soil and increases the risk of erosion. According to Larney, dry beans have now been bred to stand up taller, making them better suited for narrow rows.
Larney and his team also planted cover crops. Cover crops are useful for two reasons: They provide a protective cover over the soil through the winter months, and they use up any leftover nitrogen in the soil after harvest. If the soil was bare in winter, water and wind would steadily chip away at it, and might cause the nitrogen to move away.
“Another name for them is catch crops,” said Larney. “They’re basically catching anything left over in the soil in terms of nutrients, rather than leaving them in the root zone where they could potentially leach into groundwater.”
They also used manure compost to bolster the organic matter in the soil. Year after year of growing crops can put a strain on organic matter levels. To combat this problem, Larney and his team added manure compost to the fields to try to replace the lost organic matter. With the large cattle feedlot industry in the area, manure is readily and widely available.
“We produce a lot of manure and a lot of that is being turned into compost,” said Larney. “Many irrigation growers are quite keen on using compost on their land, and we found that we could improve soil quality over time if we applied the compost.”