Alternatives to Summerfallow
The practice of fallow (not planting a crop for one growing season) has long been considered an effective risk management tool for producers. In drier parts of the Prairies, fallow (also called summerfallow) helps to build up soil moisture reserves. The practice has also been used in wetter areas (that is, parkland) to more effectively control problem weed infestations.
However, over the past 20 years, fallow has increasingly come under attack for contributing to environmental degradation. The burial of crop residue associated with the use of tillage to control weeds leaves the soil more exposed to wind and water erosion, and increases organic matter loss. Soil organic matter loss also contributes to production of carbon dioxide, one of the greenhouse gases. Under wet conditions, fallow can contribute to increased leaching of water below the root zone and increased surface water runoff. This can lead to increased salinization (primarily in drier areas), water erosion, and potential contamination of surface and groundwater with nutrients and pesticides (primarily in wetter areas).
Improved farming practices over the past two decades have resulted in a reduction in fallow acres, as well as improved fallow management techniques that minimize negative impacts. In wetter areas, the need to fallow has been largely eliminated through improved weed control strategies such as diversified crop rotations, low soil disturbance seeding methods, reduced tillage, and the judicious use of herbicides.
These strategies have enabled producers to maintain more crop stubble and straw cover (also called residue) on the soil surface. This has resulted in improved moisture conservation through better snow trapping and reduced evaporation. As a result, many producers in drier areas have been able to eliminate or reduce the frequency of fallow in their crop rotations.
Nevertheless, even with the best moisture conservation techniques, there are instances where it is too dry to successfully grow a crop every year. This would include areas within southwest Saskatchewan and southeast Alberta that regularly experience drought conditions. Periodically, severe drought conditions can extend over larger areas across the Prairies.
The main goal of sustainable fallow management is to conserve as much residue from the previous crop as possible, while at the same time controlling weed growth. Options available for this purpose include herbicides, reducing tillage speed, and using wide blade cultivators or regular cultivators with low crown sweeps which retain more residues than disk-type equipment.
These practices will often be sufficient to protect soils from erosion. However, in some instances the previous crop may not leave enough residue. This is often the case with pulse and oilseed residues, which ideally should not be fallowed. Following a year of drought, which we have just experienced, there is little residue even on fields that were in cereal crop. As a result, fields to be fallowed in 2002 will likely require additional management to protect against erosion.
The best way to enhance erosion protection is to increase vegetative growth during the fallow period. This can be done by seeding annual barrier strips, green manure crops, or cover crops. The key is to allow enough growth to provide erosion protection, while limiting that growth to avoid removing excessive moisture. Some of the moisture lost by crop growth can be recovered through improved snow trapping. Another alternative is to allow weeds to grow taller before they are killed, as long as weed growth is terminated before seed set. One also needs to consider that some weeds are only susceptible to herbicide control at earlier growth stages.
Other practices that can reduce wind erosion risk include the use of shelterbelts and realigning field boundaries so that the shorter field width is parallel to the prevailing wind direction. These practices require more careful planning and take several years to implement.
Another alternative to fallow should also be considered. Quite often, fields that are most susceptible to environmental damage, especially during fallow, are also the least productive from an agricultural perspective. This would include land with sandy soil texture, steep topography, or moderate to severe salinity. This land should be removed from annual crop production, and seeded to a perennial forage. Other environmentally sensitive areas such as land close to lakes, sloughs, streams, waterways, and dugouts should also be seeded to perennial forage. It could be argued that areas which have experienced considerable drought historically should also be converted from annual crop production to perennial forage, due to frequent crop failures and high wind erosion risk.
Considerable progress has been made in reducing fallow acres and improving fallow management across the Prairies. However, more work is needed to eliminate fallow in wetter areas. In drier areas, opportunities exist to reduce fallow frequency through improved moisture conservation techniques, and to improve fallow management by conserving crop residue and enhancing vegetative growth when residue levels are low. There is also a need to convert environmentally sensitive land to perennial forage.
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