Summerfallow

Summerfallow or fallow is the practice of allowing land to lie idle during the growing season. Traditionally farmers use summerfallow one year as a risk-management strategy to improve the chances of growing a crop the following year; during the fallow year, farmers control weeds by either tilling the land or spraying herbicides. In the dry prairie climate, the success of agriculture is largely dependent on farmers' ability to manage water. The value of summerfallow in Saskatchewan was discovered by accident in 1885 when the Qu'Appelle Valley Farming Company of Indian Head provided horses and wagons to transport military supplies for the North-West Resistance: the land that was allowed to lie fallow that summer had more moisture and hence a larger crop in 1886. By 1889, the Indian Head Experimental Farm reported that “fallowing the land is the best preparation to ensure a crop.” Up until the 1960s, summerfallow was widely promoted as sound agriculture practice on the prairies.

The main objective of summerfallow is to increase soil water reserves; during the fallow year, it is necessary to control weeds by either tilling or spraying herbicides. While only 30% or less of the precipitation from the fallow period is conserved, this additional moisture helps ensure there is adequate moisture to grow a crop the next growing season. A secondary benefit is the release of plant nutrients from the soil organic matter, which reduces the need for fertilizer applications in the subsequent crop. Additional rotational benefits include providing breaks in insect and disease cycles. Since the fallow year has no production, farmers must recoup their costs and make up for the lost production in subsequent years. In the drier areas of the prairies, land traditionally lay fallow every second year. In areas with better moisture conditions, the economics of summerfallow production are less attractive: land is either continuously cropped or left fallow every third or fourth year.

Summerfallow also has several major disadvantages. While many people have long believed that resting the land with summerfallow was good for the soil, scientists concluded that long-term use of summerfallow degrades soil quality and is not sustainable. The main soil degradation issues associated with summerfallow are soil erosion, soil organic matter depletion, and soil salinity. Since the soil on fallow land is left bare for long periods of time, the exposed soil is vulnerable to wind and/or water erosion. While wind erosion occurs every year, severe dust storms are more common in drought years like those experienced in the 1930s and late 1980s. On sloped topography, exposed soil is easily washed away during intense rain storms or spring snowmelt. Conservation practices developed to address these problems include strip-cropping, field shelterbelts, and conservation tillage. Recently, the use of non-selective herbicides like Glyphosate (Roundup™) to control weeds in fallow has become more common; this practice, known as chemfallow, leaves the previous year's crop residue on the soil surface to protect it. During a summerfallow year, soil microorganisms mineralize soil organic matter, releasing soil nutrients; this provides the short-term benefit of providing nutrients for the following crop. Since few fertilizer inputs are used on summerfallow land, over the long term the soil's natural fertility is slowly mined from the soil organic matter in the form of harvested grain. Currently, scientists estimate that 30% of the soil organic matter has been lost since cultivation began.

Soil salinity is a state where the soil contains enough dissolved salts to hinder plant growth. Summerfallow is considered a major cause of increasing salinization of soils. It does this by raising the soil water table in sensitive areas: salts move with the rising groundwater, and accumulate in the root zone and on the soil surface. Current estimates show that 38% of prairie farmland is affected by salinity to some degree. Over the past forty years, agrologists have worked with farmers to develop farming systems that make better use of limited soil water resources while reducing the need for summerfallow. The key to these systems is better snow trapping: this is achieved with conservation tillage practices such as direct seeding, which leave the crop residue standing to trap snow and improve water conservation by reducing evaporation losses associated with tillage. Pest cycles are broken by using more diverse crop rotations. As a result, there has been a steady decrease in the use of summerfallow since the mid-1970s: the percentage of cultivated land in Saskatchewan in summerfallow dropped from 38% in 1976 to 16% in 2001.

Blair McClinton

Print Entry

Further Reading

Gray, J.H. 1996 (1967). Men Against the Desert. Saskatoon: Western Producer Prairie Books; MacEwan, G. 1980. Illustrated History of Western Canadian Agriculture. Saskatoon: Western Producer Prairie Books.