Date of this Version
Published in Soil Management: Building a Stable Base for Agriculture (2011) 287-300. DOI:10.2136/2011.soilmanagement.c19
Fallow has been defined as a farming practice wherein no crop is grown and all plant growth is controlled by cultivation or chemicals during a season when a crop might normally be grown. (Haas et al., 1974). Fallow as a practice, associated with crop rotation, had its origins in Mediterranean agriculture (Karlen et al., 1994) and continues to be used throughout the semiarid and arid regions of West Asia and North Africa (Ryan et al., 2008). Additionally, summer fallow has been practiced widely across the 15 western states of the United States and the farmed areas of the prairie provinces of Canada in response to widely varying precipitation from year to year. For example, precipitation in any given year for a specific site in the central Great Plains region of the United States may range from double to less than half of the long-term average (Greb et al., 1974).
The primary reason for summer fallow is to stabilize crop production by forfeiting production in one season in anticipation that there will be at least partial compensation by increased crop production the next season. Summer fallow was almost universally adopted in the semiarid U.S. Great Plains in response to the 1930s dust bowl, higher wartime prices, and much improved tractor power systems and implements needed to control weeds during fallow (Greb, 1979). Other objectives of fallowing are to maximize soil water storage through improved water intake, snow trapping, and decreased evaporation; maximize plant nutrient availability; minimize soil erosion hazards; and minimize energy and economic inputs (Greb, 1979). Soil texture determines water holding capacity, thereby influencing how well fallow can buffer the influence of variable growing season precipitation on crop yield.