Termination strategies for perennial forages in cropping rotations

Including perennial forages in crop rotations is an effective way to improve soil quality while producing a crop that is beneficial to both livestock and annual crop production systems. Producers often hesitate to include perennial forages in crop rotations due to the establishment and termination challenges associated with these crops.

Hay or pasture can be converted to annual crops by using tillage, herbicides, or a combination of both. The effectiveness of forage stand termination is dependent on termination method, timing, stand composition and environmental conditions. Here are some forage termination options:

Tillage

One option for forage termination is using tillage to work down the stand. A survey of Manitoba and Saskatchewan forage producers found that when tillage was used as the primary method of termination, five to seven passes across the field may be required to terminate the forage stand and prepare a suitable seedbed for the next crop. The numerous passes across the field can bring considerable wear-and-tear on equipment, as well as lost time and significant financial cost.

When intensive tillage is used to terminate a forage stand, soil improvement benefits associated with growing forages may be reduced. Intensive tillage can destroy soil aggregation and forage root channels which increase water infiltration. Tillage can also dry the soil through increased evaporation.

Tillage & Herbicides

Another option for forage stand termination is to use a combination of tillage and herbicides. Effectiveness of forage stand termination can be improved by substituting herbicide use for some tillage operations. This can be accomplished with an initial herbicide application in the summer or fall of the year prior to seeding, or prior to working the stand in the spring prior to seeding. When applying herbicides in early spring, control of perennial forages will be reduced as this is not the ideal stage for maximum effectiveness. The non-selective herbicide glyphosate is the most commonly recommended herbicide registered for forage stand termination.

Herbicides

Forage stand termination can be completed using herbicides exclusively to kill the perennial forage crop. Annual crops can then be direct seeded into the sod. Termination with herbicides provides a soil environment conducive to germination and establishment, as the seed bed is minimally disturbed and moisture conservation is maximized. Where no option for a summer or fall herbicide application is available in the pre-seeding year, herbicides can be applied in the spring prior to seeding. However, early spring applied chemical is less effective as the forage plants have not yet reached the optimum stage for chemical control.

Reduced tillage results in increased crop residue on the soil surface either as standing stubble or as mulch and can increase conservation of soil moisture. Based on research from Manitoba, Saskatchewan and North Dakota, a stubble height of 20 to 25 centimeters, when full of snow, can account for two to five centimeters of soil available water. When intensive tillage is used, snow capture is reduced, water infiltration is decreased, the risk of wind and water erosion is increased, and evaporation is increased. Thus, termination strategies that minimize tillage are more likely to conserve soil moisture as opposed to strategies that rely predominately on tillage. This is of particular importance in the drier regions of the Prairies, such as the Brown and Dark Brown soil zones, where soils dry quickly and soil moisture deficits are common.

When choosing a termination strategy, consider how effective it will control problem weeds such as quackgrass, foxtail barley, dandelion and Canada thistle. For example, tillage of quackgrass, foxtail barley or Canada thistle can result in ineffective control of these weeds, and in some cases, may increase these weeds; however, a fall herbicide application can result in excellent control as translocation of chemical into the roots occurs. In contrast, dandelions can be controlled better with tillage, as some herbicides such as glyphosate can be relatively ineffective.

Other factors to consider when choosing a termination strategy include, but are not limited to, topography and the presence of stones or burrowing animals. Abundant stones or uneven topography may favour herbicide use over tillage. On the other hand, tillage may be needed to prepare an even seedbed when mole hills are present.

In recent years, most forage stands have been terminated with some degree of herbicide use. Regardless of the method of forage stand removal, it is important to plant a crop that will allow for good in-crop control of weeds and any surviving forage plants.