Fall and full-season cover crops show promise in potato trials

Some varieties have shown yield increases and erosion control

Canopeo images of establishment of spring barley and fall rye for the P.E.I. cover crop trials showing establishment rates depending on the plant dates and seed rates. All images were captured Nov. 17.

Cover crop trials in Prince Edward Island potato fields are yielding promising results.

Over the last two years, Ryan Barrett, research and agronomy specialist, Prince Edward Island Potato Board, has run fall-seeded and full-season cover crop trials to assess if there are an overall soil and potato harvest benefit.

Why it matters: An estimated 80 per cent of soil erosion happens during heavy rainfall events in the spring in the fall – a quick-growing cover crop would hold soil, avoiding washouts, rail and gully erosion seen on potato fields.

Barrett ran fall-seeded cover crop trials of spring and winter cereals in 2019 and 2020 to test the impact and effectiveness of a cover crop on potato fields using various seeding and establishment methods and pre-and-post-harvest plant dates.

The spring barley trials utilized three different seeding dates and rates. Barrett planted 100 lb. per acre on Oct. 1 and Oct. 8 and the third at 150 lbs. per acre on Oct. 12. He used Canopeo, a smartphone app that analyzes establishment, to measure the progression. The first plant date hit 44 per cent establishment by Nov. 17, the second had 19.47 per cent coverage and the final plant 4.04 per cent establishment, he said.  

“Timing makes all the difference in the world when it comes to establishment date, particularly for your spring cereals,” he said.

A second trial tested a pre-harvest with a harvester incorporated seed broadcast of fall rye on Oct. 3, against a post-harvest application of lightly harrowed-in seed on Oct. 6. The pre-harvest reached 18.14 per cent establishment by Nov. 17 and the post-harvest was 12.12 per cent according to Canopeo, said Barrett.

The 2020 field trials showed a 50 per cent coverage rate, and a soil nitrate leaching reduction of up to 75 per cent. Barrett noted early-planted cover crops performed well across the board, with spring cereals being less reliable past Oct. 5 in P.E.I. and winter barley, wheat and fall rye doing well up until Oct. 15 plant dates. 

While fall rye is a favourite due to its reliable establishment with early and late planting dates, weed control potential and spring regrowth, winter barley is showing promise with faster emergence and higher coverage against winter wheat. 

“It’s going to be very dependent on where you’re at, your field conditions and the growing season itself ... but generally, the later you plant the more challenging it is to get establishment,” he said. 

“The average yield improvement was somewhere around 1,500 hundredweight per acre on total yield and about 1,000 cwt. per acre on marketable yield,” said Barrett. “And about $154 an acre improvement in crop value.”

The 12 comparisons of alternative crop versus check crop were encouraging, said Barrett, with a significant increase in marketable yield in four of the comparisons and no significant decrease due to the cover crop. 

Forage pearl millet and sorghum sudangrass showed promise with the ability to be under-seeded with legumes and grasses to provide hay or silage to establish a forage crop while maximizing cover crop benefits, he said. 

Forage and legumes have traditionally preceded potatoes in P.E.I., particularly red clover, said Barrett, which is good for soil organic matter and early season fixing of nitrogen but is also a multiplier of root lesion nematodes. Forage pearl millett is not and provides soil conditioning and fights compaction.

“That’s a huge thing in potato rotation where often root lesion nematodes can be really high,” he said, adding P.E.I. has had issues with root lesion nematode population.

Research performed by Agriculture Canada in PEI also showed a 10 to 15 per cent yield increase with warm-season C4 grasses compared to red clover on a plot basis, with forage pearl millet performing the best, Barrett said. 

Biofumigation trials with a high-glucose simulate variety of brown mustard have shown yield increases of 30 to 50 cwt. per acre and reduced wireworm damage, Barrett said, but wider basis replication is needed. 

Barrett said it’s easy to get caught up with fads, which is why looking at the research data and figuring out which option suits the farm or field’s specific needs is key. 

The cover crop rotation should meet the needs of a primary profit generator – potatoes – not interfere with or lower yield, but he said, don’t sacrifice long-term soil health and success for a short-term gain. 

About the author

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Diana Martin

Diana Martin has spent more than two decades in the media sector, first as a photojournalist and then evolving into a multi-media journalist. Five years ago she left mainstream media and brought her skills to the agriculture sector. She owns a small farm in Amaranth, Ont.

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