OUTLOOK, Sask. — Researchers are looking at how including fababeans in a crop sequence could benefit soil carbon and improve other environmental factors when potatoes are also part of the rotation.
So far, their hypothesis is holding true.
Dr. Reynald Lemke, who is based at the federal research centre in Saskatoon, said the study is in its third year at the Canada-Saskatchewan Irrigation Diversification Centre in Outlook. The trial is also underway in Carberry, Man.
Many studies of dryland systems have shown benefits to the following crop when there is a nitrogen-fixing legume in the rotation.
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The idea in the irrigated canola-wheat-fababean-potato rotation is to examine the effect of the previous crop residue on both the soil and the potatoes.
Wheat residue is high carbon, while canola residue is considered a bio-fumigant residue.
“We presume that including an annual legume into this sequence may result in some benefits,” Lemke said.
Fababeans were a deliberate choice because they are strong nitrogen fixers, which might increase the benefit to the following crop.
“It also generally produces a lot of biomass so you get some additional soil carbon into the soil,” Lemke said.
“One of the concerns about potatoes is it’s unavoidable — it’s going to be a high disturbance growth year, and so it’s probably safe to assume it’s going to have some impact on soil carbon status, soil structure and general soil quality.”
He said fababeans could also possibly reduce greenhouse gas emissions.
Canola, wheat and fababeans were grown in the first year of the study, followed by potatoes in the second year at nitrogen rates of zero, 30, 50 and 90 kilograms per acre. Wheat is now being grown on those fields at two fertilizer rates.
All fields are being sampled for greenhouse gas emissions.
“Just looking at the data at this point in time, our hypothesis that fababean might be a very good crop in the sequence from an environmental point of view appears to be holding out,” Lemke said.
Results are still preliminary, although last year the Carberry site reported no effect on potato yield or quality from the previous crop.
At Outlook, the highest potato yield after canola resulted at the 30 kg nitrogen rate. After wheat, the highest yields came at the 90 kg rate.
“Potatoes grown on fababean more or less matched those highest values, but at the zero nitrogen rate, so you have what looks to be a real benefit,” Lemke told a field day earlier this month.
“You’re getting at least as good yields with much less fertilizer.”
There is still a lot of information to pull out of the data as far as the effect on greenhouse gas, but he added that active carbon remained relatively unchanged between the first and second years of the study.
