“One of the biggest things that affects moisture is the maturity differences of your crop.”
Avoiding disease and herbicide resistance are two well-known reasons for crop rotation, but there are others, including moisture availability, says a Manitoba agronomist.
Anastasia Kubinec, oilseed business specialist with Manitoba Agriculture, outlined crop sequence considerations for canola growers at the Canola College held here in February. Her research was part of a joint partnership with Stewart Brandt of the Agriculture Canada research facility in Scott, Saskatchewan.
Kubinec says crop sequencing has a definite affect on soil moisture levels.
“One of the biggest things that affects moisture is the maturity differences of your crop,” said Kubinec. As crops start to mature, they use less water. If a crop has an early maturity level or can be harvested earlier, it generally leaves more water behind for the next crop.
Perennials have deeper roots than crops such as pulses, and root depth affects the level at which the water is leaving the soil. This has an impact on how much water is available for the next crop. In taller-stubble crops such as cereals or mustard, snow is trapped more effectively than in shorter-stubble crops such as peas, lentils or flax, providing more moisture.
Weed control is another consideration when planning a crop rotation, said Kubinec.
Control of broadleaf weeds is easier in a cereal crop, and grassy weeds are easier to control in wheat crops. “It’s also more economical to control cleavers in wheat, and you have more options,” Kubinec said. “You’re working on your herbicide rotation as well and could potentially clean up some of your fields.”
Disease control is another factor when planning a crop rotation. Changing crop types can break the cycle of disease buildup and will reduce the possibility of disease.
Planting canola after canola can increase the possibility of sclerotinia or blackleg. “If you have canola after wheat, there’s definitely no risk there. That’s definitely something to keep in mind,” she said.
Nutrient use is another factor to consider and producers should ask themselves what the last crop will be able to give to the following crop. For example, nitrogen-fixing crops such as pulses will give a boost to the next crop and save on fertilizer costs.
Nutrient recycling can also increase depending on the properties of the residues. “With your pulses, as the residue breaks down, you will get that nitrogen boost,” said Kubinec. “When cereal breaks down, you may have a slower nitrogen release as it produces more carbon. These factors may impact what you plan for your next crop, but what it really all comes down to is yield,” she said.
Research trials run by Stewart Brandt and his team found that putting a cereal on oilseed stubble could increase yields by up to 35 per cent. An oilseed planted on cereal stubble could result in a boost of about 50 per cent. Putting oilseed or cereal crops on pulse stubble also results in yield boosts.
Winter wheat planted on canola stubble resulted in a boost of 37 percent yield for the winter wheat. Spring wheat planted on canola stubble resulted in 14 per cent higher yields.
Kubinec said the results from the research trials are confirmed by Manitoba crop insurance data on actual results by farmers.