GHGMP Project Reports by Region

Relay cropping produces top forage, benefits environment

Fast growing grass provides ground cover and helps reduce surplus nitrogen

Italian rye grass inter-seeded with corn in the spring is helping B.C. Lower Mainland farmers use surplus soil nitrogen and at the same time produce an excellent forage for livestock, says a Agriculture and Agri-Food Canada Researcher at Agassiz.

Relay crop field 1

The practice, known as relay cropping, is beginning to catch on among dairy producers, says Dr. Shabtai Bittman, a forage and field crop management specialist at the Pacific Agri-Food Research Centre (PARC). "The Italian rye grass, over its growth cycle will remove about 100 kilograms of surplus nitrogen per hectare," says Bittman. "And it is one of the top forages to produce. It's a leading forage in New Zealand and Europe."

Relay cropping further benefits the environment by significantly reducing the amount of nitrogen lost through leaching and to the atmosphere. The research project, co-ordinated through the Pacific Field Corn Association, is supported in part with funds from the federal Greenhouse Gas Mitigation Program for Canadian Agriculture (GHGMP).

Forage seeded with corn

The concept is to seed a second crop with the corn that will continue to grow and use surplus nitrogen once the corn has been harvested, says Bittman. After looking at several options over the years, Italian rye grass emerged as one of the most suitable forages.

Relay crop field 2

The Italian rye grass is inter-seeded when the silage corn is between the three to six leaf stage, which explains the term relay cropping. "It won't compete with the corn at that stage, and yet there is enough sunlight to allow the Italian rye grass to establish," he says. Growth of the rye grass is suspended once the corn crop canopy closes. But after the corn is harvested, in late September or early October, the rye grass begins growing again.

"It usually takes about 10 days after corn is harvested for the Italian rye grass to take off," says Bittman. "But it continues to grow into December." Bittman estimates the rye grass uses between 50 and 65 kilograms of nitrogen per hectare in fall. After resuming growth, usually in February, it will use another 40 to 50 kilograms of nitrogen before harvested as silage, greenfeed or used as pasture.

"The rye grass is not able to use all the surplus nitrogen in the soil, but it makes a significant difference," he says. "On average the crop removes about 100 kilograms of nitrogen per hectare whereas without it, surplus nitrogen use would be zero."

Environmental concerns

Surplus nitrogen in the usually heavy winter rainfall area of south-coastal B.C. causes major environmental concerns, points out Sandra Traichel, with the Abbotsford Soil Conservation Association and a field co-ordinator for the federal GHGMP in B.C.

Surplus nitrogen can be leached from soil and enter the groundwater, she says. And in waterlogged soil, it is also subject to a process of denitrification, which means the nitrogen is converted and released to the atmosphere as nitrous oxide, one of the more serious greenhouse gasses.

In two years of trials comparing application of manure on bare soil with manure application on grass fields, research showed a dramatic reduction in the production of nitrous oxide. "Vigorously growing grass really soaks up the nitrate," says Bittman. "We found a five to 10-fold reduction in nitrous oxide production on grassland compared to bare fields. It makes a significant difference."

Relay crop field 3

To maximize the benefit of relay cropping it's important to use a forage with high feed value, says Bittman. Earlier research found fall rye also works as a relay crop, but it makes poor livestock feed. "Producers are inclined to plow it under rather than harvest the feed," he says. "And that practice just returns the nitrogen to the soil, so we don't really gain anything."

Excellent forage

But Italian rye grass has proven to be a valuable forage for dairy cattle. A very palatable forage with good protein, the crop can yield three to five tonnes per hectare and be used as silage, green feed and pasture.

Producer interest in relay cropping in Canada was slow in coming, says Bittman. Some U.S. Pacific Northwest producers saw relay cropping trials in B.C. and jumped on the practice much earlier. One reason is the U.S. producers had access to a herbicide which could effectively control barnyard grass that grew along with the Italian rye grass. Canada now has a registered herbicide to control the weed and not harm the forage.

A second reason for speedy U.S. adoption, was interest by at least one company to provide a custom service for inter-seeding the Italian rye grass into corn. "It made quite a difference for northern Washington and Oregon producers just to be able to hire someone to do the seeding," says Bittman. "Producers here are set up for row crops, but not all have access to grain seeding equipment."

Producer tours showing the success of relay cropping has generated considerable interest among B.C. producers. "One producer on southern Vancouver Island who has been relay cropping for several years is getting exceptional yields, and this year he had half his crop harvested by early April," says Bittman.

"It has proven to be an excellent forage," he adds. "And the grass crop plays an important role in reducing the impact of surplus nitrogen on the environment."

Regional reports will be posted as information becomes available. Please check back regularly for updates.