Intercropping research explores benefits, downsides

More and more prairie producers are showing an interest in intercropping, the practice of growing two or more crops together in the same field.

What crops grow well together and under which circumstances are still being determined by a growing number of research projects across the Prairies.

In 2015, Saskatchewan Agriculture planted a pea-cereal intercrop for green feed that generated so many farmer questions that researchers decided to create a new research project to address them.

University of Saskatchewan researcher Bill Biligetu helped develop the project at Saskatchewan Agriculture where he evaluated forage peas grown with a barley or oat forage variety.

The standard seeding recommendation for a pea-cereal mixture in Saskatchewan is 100 percent of normal pea-seeding rate and 30 percent of normal-seeding rate for the cereal-crop component.

“But most of the pea crops have a very expensive seed cost,” Biligetu said. “So the first question is, can we reduce the legume portion or the forage pea portion to 50-50?”

“The second question is how much yield are we going to get and what’s the protein level?”

He said growers of forage intercrops tend to add nitrogen to boost the yields of the cereal crop, so Biligetu wondered whether applied nitrogen reduced the nitrogen fixed by the pea and thus negating the benefit from the legume.

The study also set out to answer whether the intercrop can dry down enough to be baled.

The project was held in three locations, Saskatoon, Melfort and Swift Current, and two different forage pea cultivars were used, 40-10 and CDC Horizon.

CDC Maverick, a newer forage barley, and the forage oat CDC Haymaker were the cereals used.

The study ran over two years, with 2016 having an average amount of precipitation while 2017 had below normal rainfall.

Researchers found that CDC Horizon yielded better than the 40-10 pea variety.

“This is mainly because they are large and resistant, they don’t lodge easily. 40-10 is kind of lodging quite badly,” Biligetu said.

The study examined a pea-seeding rate set at 50 percent of normal, and the forage cereals planted at 50 percent of normal instead of the recommended 30 percent.

“We used 50-to-50 ration, and we didn’t really see any yield reduction and in some cases we actually saw yield increase because we have more cereals in the mixtures.”

However, a disadvantage was noted.

“The forage pea is not a very competitive crop. So when we reduced 100 percent to 50 percent, we see a reduction of forage peas dry matter in the mixtures. So that translated to protein level decline,” Biligetu said.

“Most of the time, when we reduced to 50-50 the forage-pea percent was around eight to 12 percent. When we have 100 percent seeding rate of forage peas, there was of anywhere from 10 to 25 percent in the dry matter.”

When protein levels of pure barley or oats were compared to the 50-50 mixture, the protein levels of the pea-cereal mixture were about 18 percent higher.

“When we increase the pea component to 100 percent, it’s 29, almost 30 percent higher than just mono culture of barley or oat,” Biligetu said.

Yields were similar between the mono culture of cereals and the intercrops.

Lodging in the 40-10 forage pea was reduced by almost half when it was grown with a cereal.

To test the effect of nitrogen applications on the intercrops, trials with 50 pounds of added nitrogen were used at all three sites, with three replications over two years.

“When we added 50 lb. of nitrogen into the stand, it only really increased yield at the Melfort site. Because it is higher moisture, that is probably one reason,” Biligetu said.

“At Saskatoon and Swift Current over two years, there was no yield increase.”

Nitrogen fixation by the pea declined at the Melfort site when nitrogen was added.

“When you’re adding nitrogen in a site such as the black soils zone where the moisture is high, it will boost the yield for cereals, but it will also reduce the nitrogen fixation,” Biligetu said.

“In a drier site the effect is really minimal. If you add a little bit of nitrogen, probably a yield increase of a small amount, but you couldn’t really see a big difference in nitrogen fixation.”

Existing soil nitrogen levels were also examined and Biligetu said in higher nitrogen areas the nitrogen fixation is not as high as in soils with lower nitrogen levels.

In 2016, drying the green feed enough to be harvested was difficult.

“By the time we were close to reaching the soft-dough stage for harvesting oat and hard-dough stage for forage barley, in Saskatoon it rained almost every other day and it took almost two weeks to dry,” Biligetu said.

“But in 2017 when it was dry, it only takes a couple days and it makes the perfect hay. It really depends on weather rather than the mixture itself.”

Under the high moisture conditions in 2016 mould was observed starting around the pea pods.

Biligetu said the study shows there is a nitrogen fixation benefit and a feed quality benefit in terms of protein in using the peas intercropped with oats and barley. However, there is also a higher cost associated with buying pea seed.

The next stage of the study is underway, which involves feeding the green feed to animals at the University of Saskatchewan and monitoring their health and gains.

It is expected to wrap up in April.

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