GHGMP Project Reports by Region

Forage project evaluates herbicide treatments as a tillage alternative

Re-establishing a forage stand without plowing and discing helps preserve soil organic matter and is also good for the environment.

Farmers in B.C.'s Peace River Region are watching a three-year demonstration project to see if there is an economical and practical way to re-establish a perennial forage stand without tillage.

While direct seeding grass and legumes into unproductive sod sounds simple, it hasn't been successful, says Julie Robinson of the Peace River Forage Association (PRFA), which is based in Dawson Creek. So now, a demonstration project, supported in part by the Greenhouse Gas Mitigation Program for Canadian Agriculture (GHGMP), is using a combination of herbicides and annual crops such as oats and barley, for at least one year, to better prepare a field for the next perennial crop.

"The difficulty with direct seeding a perennial back into an unproductive hay or pasture stand is getting good stand establishment and good weed control," says Robinson, who is also field co-ordinator for the soil and beef sectors of the GHGMP in the northeast B.C. region.

"We thought we might be able to direct seed perennials into unproductive pastures thereby rejuvenating the stand in year one, but that didn't work," she says. "We ended up with a very patchy stand and too many weeds." A better strategy is to spray out the old forage stand with a herbicide, direct seed an annual crop such as oats or barley for preferably two years, and then re-establish the new perennial crop into the cereal stubble.

The objective is to develop a system that eliminates the need for breaking the sod and working the field. A decent hay or pasture stand will produce about 2.5 tonnes of forage per acre, but as the stand ages and production drops to about one tonne of forage per acre or less, the field is usually tilled and reseeded.

Sequester carbon

"With discing and plowing there's always the concern about water erosion until the new crop is established," says Robinson. "There's also the cost of the four or five tillage passes needed to break and cultivate a field. At today's fuel prices, that isn't cheap. And from an environmental standpoint, cultivation affects soil structure and also releases carbon dioxide, a harmful greenhouse gas, into the atmosphere."

A healthy, productive forage stand captures carbon dioxide from the atmosphere and stores or sequesters it as carbon in plant leaves and roots and in the soil. Conventional tillage, which breaks the sod and exposes the soil, releases that sequestered carbon.

The sod layer of the forage crop provides readily available nutrients to the plants and organic matter, which also helps maintain soil structure. If the pasture or hayfield is plowed, however, that organic matter is buried five to six inches deep, making it difficult for cereal crop seedlings to access the nutrients. "In some of our soils in this region, by plowing and discing, we lose the soil structure and access to the organic matter, which is very minimal to begin with," says Robinson.

The GHGMP-funded project, working on two sites, is evaluating different herbicide timings to determine if a fall and spring treatment is needed or just a fall treatment is sufficient to control weeds before the annual crop is directly seeded. Different herbicides and different combinations are being used.

Fall only treatments

At one site, which was a perennial hay and pasture stand until 2003, a Flexi-Coil air drill equipped with Barton openers was used to direct seed a cereal crop into sod in 2004 and again into stubble in 2005. In the fall of 2005, several 10 metre by two metre plots were treated with different herbicide combinations. The plots may be sprayed with a 1.5 litres of glyphosate per acre in early 2006 before seeding. Legume and grasses will be direct seeded into the old sod and annual crop stubble this spring.

The weed control program last fall included seven different treatments, explains Robinson. The demonstration plots were treated with:

  1. 1.5 litres of glyphosate per acre
  2. 1 litre of glyphosate per acre
  3. 1.5 litres of glyphosate combined with 0.5 litre of 2,4-D per acre
  4. 1.5 litres of glyphosate combined with Express at the four grams per acre rate
  5. 0.5 litre of PrePass combined with 0.5 litre of glyphosate per acre
  6. 0.5 litre of PrePass per acre
  7. a check plot, with no herbicide treatment.

The question is whether the fall herbicide treatment along with one or two years of a cereal crop is adequate to control weeds before the perennial crop is re-seeded.

The second site was a worn out hayfield on a hillside, which had a few remaining alfalfa plants and was overrun by dandelions. It was still in forage production through 2005.

Fall and Spring treatments

The fall 2005 plot herbicide treatments, which are to be repeated prior to seeding in 2006, included:

  1. 0.4 litre of Curtail combined with 1.5 litre of glyphosate per acre
  2. 0.5 litre of 2,4-D combined with 1.5 litre of glyphosate per acre
  3. 1 gram of Ally combined with 1.5 litre of glyphosate per acre
  4. 1.5 litres of glyphosate per acre
  5. 2 litres of glyphosate per acre
  6. 0.5 litre of PrePass per acre
  7. a check plot, with no herbicide treatment.

Oats and/or barley will be seeded on the plots in the spring of 2006. Aside from the demonstration plots, the rest of the field was treated with a 1.5 litre rate of glyphosate last fall. The balance of the field will get another glyphosate treatment in early 2006 before seeding. This field won't be seeded back to a perennial forage stand until 2007.

This summer the PRFA will work with Calvin Yoder, an Alberta Agriculture, Food and Rural Development forage specialist from Spirit River, Alberta, to conduct a plant count on the treated sites to determine which timing and which combination of herbicide was the most effective.

"Overall, we also need to look at herbicide economics," says Robinson. "PrePass, for example, is an effective broad spectrum, pre-seeding herbicide, but at about $15 per acre, it is expensive," she says. "We want to see if perhaps a less expensive treatment, such as glyphosate and 2,4D, for example, will do the job just as well."

A report on the results of the various treatments should be ready by the fall of 2006.