Pulse crops in a tight rotation

Lower crop emissions, such as N2O, in crops such as lentils green the farm footprint. | File photo

Pulse crops have been a significant part of rotations in Saskatchewan for decades. The question is how tight of a rotation is safe?

Pulse crop benefits includes breaking cycles of weeds, disease and insects. Plus there’s the nitrogen-fixing factor farmers depend on when they follow a pulse crop with a cereal. But growing pulses crops on the same field too often can have negative consequences.

The issue of how tight pulse crop rotations can be is being addressed by Kui Liu, research agronomist at the Swift Current, Sask., Agriculture Canada research centre.

Liu presented a report on his early findings this winter at the Saskatchewan Agronomy Update.

The objective of Liu’s research is to develop productive and sustainable cropping systems for the Prairies. The project started in 2018 and will is scheduled to run through 2022.

Six experimental cropping systems are being tested in four-year rotations.

1) CCS – Control – Conventional Cropping System

2) POS – Pulse/Oilseed Intensified System

3) DS – Diversified System

4) MS – Market Driven/Profit Maximization System

5) HRHRS – High-Risk/High Reward Innovative System

6) GMS – Green Manure Soil Health Enhancement System

In his presentation notes, Liu said, “For yield, MS system had the highest yield, POS had the second highest yield.

For stability, POS had the above-average yield stability. Pea followed by wheat produced the highest protein because of the high yield of both crops.”

Liu observed that chickpea-pea did not show expected protein benefits compared to wheat monoculture, due to low chickpea yield because of ascochyta blight and weed issues under intensified chickpea rotations.

“Lentil-lentil-lentil-wheat generated the highest net revenue. This was a surprise for me, probably for most of you too. But I would not grow lentil three years in a row if I were a farmer. High frequency can cause a severe disease outbreak.”

“This is a plot-scale study, so we probably sprayed more fungicides than what a typical producer does. Our disease management might have reduced pathogen accumulation over the study periods, which might delay the disease outbreak. So, a long-term study is needed to test this. In addition, a high frequency lentil might cause soil quality degradation concern due to low crop residue input from lentil.

“The results also indicate that diversified cropping systems involving lentils can generate great economic revenue. It demonstrated the benefits of crop diversification with pulse crops. These diversified rotations are the recommended cropping systems.”

Liu tracked the response of wheat in the various rotations. In the wheat year, all treatments received the same amount of chemical fertilizer nitrogen.

He said N2O emissions were significantly higher in the wheat monoculture than in pulse-based rotations. There was no difference among the pulse-based rotations. Low N2O emissions in the pulse-based rotations might be due to high nitrogen-use efficiency.

Peas and lentils generally increased the subsequent wheat yield because of nitrogen benefits and the fact that their shallow root systems do not tap into deep soil profile water.

The deep-rooted chickpea, on the other hand, can either positively or negatively affect subsequent wheat yield, depending on whether or not the roots draw from the deep soil profile water in dry year, leaving less water to the following wheat.

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