Keeping hemp company

Studying ways to maximize agricultural potential by underseeding hemp crops

Hemp underseeded with clover.

One Manitoba agriculture research group is trying a few new things with hemp that involve the crop sharing the land.

In 2017 and 2018, the Westman Agricultural Diversification Organization (WADO) conducted a study on relay and intercropping with hemp. With most of the data in from that two-year study, WADO’s Scott Chalmers spoke to an audience at the Western Canadian Hemp Trade Alliance conference Nov. 21.

“Relay cropping” refers to the planting of two or more crops with staggered outcomes and “intercropping” is the planting of two or more crops at the same time, in the same space and harvested at the same time. Collectively, both of these methods are called “companion cropping.”

The study was designed to delve into:

  • Increasing fertilizer efficiency;
  • Maximizing crops per acre;
  • Increasing growing time;
  • Light use efficiency;
  • Soil health;
  • Alleviating climate risks (drought or flooding);
  • Maximizing income/acre; and
  • Salinity (a water management issue).

The WADO trials were a randomized complete block design with three repetitions. They had a control (check) for hemp grown alone and the other blocks included sweet clover, alfalfa, red clover, hairy vetch, field pea, and fall rye.

The idea was to look at each of these companion crops to analyze the potential benefits that could be realized from underseeding. For instance, they would look at how peas work to counterbalance the nitrogen economy of the soil. For the clovers and alfalfa, they would look at how it adds value to the land by allowing for grazing after the hemp crop has been harvested. They would look at how each crop acts in terms of water use per acre. They would also look at how each of the crops would affect grain output (hemp seeds and peas).

Both 2017 and 2018 were very dry in the spring. As a result, Chalmers said it was difficult to get things going.

“We only had 68 per cent of our normal rainfall in 2017,” he noted.

Then after some moderate rains in July, there was virtually no rain in August. In 2018, it was similarly dry. So, while the similar conditions were good for statistical comparison, the yields weren’t as high as they would have been with normal rainfalls. But the data did reveal some interesting results.

Grain yield 2017. photo: WADO

In 2017 there was a yield of 347 kg/hectare with peas. Neither the red clover nor the sweet clover really impacted the hemp seed yield. But with alfalfa and hairy vetch, there was a depression in yield.

“That’s just because those two crops are very aggressive. Moisture was the limiting factor,” Chalmers said.

2018 was a mirror image for moisture compared to 2017, which means there were correspondingly similar results. In 2018 the crop planted with peas showed even more pronounced overyielding (as a percentage compared to the control) despite lower yields overall (only 284 kg/hectare). But even with those promising results, Chalmers questioned whether it would be enough to make it worthwhile.

“Is it really worth chasing 200-300 kg/ac. of peas? You’d have to factor it into your costs,” he said. “To me, it’s hardly worth cleaning out that crop.”

Grain yield 2018. photo: WADO

About a month after harvest, alfalfa and hairy vetch were doing very well. Sweet clover and red clover were there, but they weren’t dominating by any means. So, while the results with the two clover crops showed they played nice with hemp in terms of yields, they weren’t as successful as the vetch and alfalfa in terms of forage value.

“For every tonne of forage in dry matter you have it’s about $40 in nutrient value or $100 in grazing value,” Chalmers said. Even though it brought down yields in hemp, the economics could work in a farmer’s favour.

“It also gives you insurance for the next year,” he said. “If you get four feet of snow followed by three inches of spring rain and you can’t get out there to seed, at least you have something to insure. Potentially you can hay it or at least have something growing other than the weeds.”

While the study has clearly provided useful information to growers who might be considering hemp, because of the unusually dry conditions, it wasn’t able to paint an accurate picture of what it’s going to look like in a normal year. Chalmers said he hopes to continue research and hopefully get data from a year with more moisture to provide more insight.

“I would love to do this on a wet year where, given enough water, we would get a huge tonnage of forage afterwards,” said Chalmers.

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