Pulses/wheat rotation studied
Farmers have long been aware of the increase in cereal yields on land seeded to pulse crops the previous year. Because pulse crops fix their own nitrogen, this advantage was perceived by farmers as being due to greater nitrogen availability.
“There were few studies to prove this, however,” said Craig Stevenson, who is completing his doctoral thesis at the department of soil science at the University of Saskatchewan.
Under supervision of research scientist Chris van Kessel in the soil science department, Stevenson and another graduate student recently completed a three-year project that examined the reason for the yield advantage of pulse crop rotations.
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“We suspected the yield advantage would be due to non-nitrogen related factors, especially the reduction of leaf and root diseases in wheat crops that follow pulse crops. Wheat diseases can’t infect pea plants, so they can’t be carried over to the next year’s crop,” said Stevenson.
The researcher’s suspicions proved correct.
“The non-nitrogen related factors were related to 91 percent of the yield advantage for wheat sown on pulse crop stubble. This advantage is most definitely not solely due to the nitrogen. We also looked at the nitrogen derived from peas and found it to be about seven pounds per acre, which has practical implications for farmers who may think they don’t have to fertilize as much after a pulse crop.”
The experiments to assess the nitrogen and non-nitrogen related factors responsible for enhanced seed yields of cereals sown on pulse crop stubble were carried out at three Saskatchewan sites. The results were an increase of three to 15 bushels per acre in the yield of spring wheat sown on pea or lentil stubble when compared to wheat sown on wheat stubble.
“The pea-wheat, lentil-wheat and wheat-wheat rotations were established on both small plots and landscape-scale plots of one hectare for each rotation,” said Stevenson.
“We found that the rotation benefit of peas was greater in the large plots than it was in the small plots. So farmers may be getting a higher yield advantage than in studies conducted in a small-plot research setting. Further research into this aspect is certainly required.”
A similar but expanded four-year study began this spring. Pea-wheat, canola-wheat and wheat-wheat rotations will be carried out at four locations in the northern grain belt.
“We are trying to ascertain whether the ratio of the nitrogen/non-nitrogen benefits will vary, and we’re monitoring weeds and diseases more intensively. A canola rotation is being tried because, if the yield advantage of peas is not nitrogen related, canola should be effective too. We’re also monitoring barley yields into the third rotation phase to see if the yield benefit carries into the third year,” said Stevenson.
For more information contact: Craig Stevenson, department of soil science, University of Sask-atchewan, 51 Campus Drive, Saskatoon. S7N 5A8. Phone 306-966-6876; Fax 306-966-6881.
