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 the termination method, timing, stand composition and environmental conditions.
Tillage
One option for forage termination is to use tillage to work down the stand. When intensive tillage is used to terminate a forage stand, five to seven passes across the field are generally required to prepare a suitable seedbed for the next crop. Intensive tillage can destroy soil aggregation and dry the soil through increased evaporation, making it susceptible to erosion. Erosion risk can be worsened by the fact that forage stands often deplete soil moisture at depth, increasing the risk of poor growth for the next crop.
Tillage and Herbicides
Another option for forage stand termination is to use a combination of tillage and herbicides. By substituting herbicide use for some tillage operations, the effectiveness of forage stand termination can be improved. This can be accomplished with an initial herbicide application in the summer or fall of the year prior to seeding, or before spring pre-seeding tillage operations. 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
A final option for forage stand termination is to use herbicides exclusively and then seed annual crops into the sod. Termination with herbicides provides a soil environment conducive to germination and establishment, as there is minimal disturbance of the seedbed, which helps maximize moisture conservation. Where a summer or fall herbicide application is not possible in the year prior to seeding, herbicide can be applied before seeding in the spring. However, as noted above, early spring-applied chemical is less effective, as the forage plants have not 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. 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.
Additional advantages to using herbicides in forage stand termination include:
- Reduction in labour and time required for seed-bed preparation;
- Reduction in fuel consumption; and
- Increased equipment savings, as less total horsepower is required for field preparation.
When choosing a termination strategy, consider how effectively 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. Tillage can also bring dormant, buried weed seeds to the surface where the environment may be favourable for germination.
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.