Submitted to: Encyclopedia of Water Science
Publication Type: Book / Chapter
Publication Acceptance Date: August 14, 2002
Publication Date: September 14, 2003
Citation: Tanaka, D.L., Anderson, R.L. 2003. Summer fallow. IN: Encyclopedia of Water Science. p. 942-945. Interpretive Summary: Water is the variable in Great Plains agriculture that determines crop production. Since the 1930's, summer fallow has been used to increase soil water storage, make nutrients available, reduce soil erosion hazards, and control weeds. From the 1930's to the late 1950's, fallow efficiencies have averaged about 16%, soil water loss due to deep percolation was negligible, ,evaporation losses were great, and evaporation potential increased from the Northern to Southern Plains. Improved technology since the late 1950's has resulted in better residue management techniques and increased fallow efficiencies to over 40%. At the present, fallow efficiencies have become stagnant and not continued increase, making the wheat-fallow cropping system unsustainable. Therefore, the frequency and the length of fallow the future will be reduced by using greater crop intensity and diversity. Fallow in the intensely managed cropping system will have new goals that include partial fallow where plants are grown for soil building and soil water enhancement, pest control, and improvement of environmental quality while enhancing our natural resources.
Technical Abstract: Summer fallow has been practiced to increase the water available for succeeding crops in areas that receive less than 500 mm of annual precipitation. Objectives of summer fallow have been to maximize soil water storage, make plant nutrients available, reduce soil water storage, make plant nutrients available, reduce soil erosion hazards, control weeds during the entire fallow period, and suppress soil water evaporation. From the 1930's to the late 1950's, research indicated fallow principles such as soil water loss due to deep percolation below rooting depth of wheat was negligible. Evaporation losses were great and fallow efficiencies were not likely to exceed about 16%, unless a practical method of reducing evaporation from north to south. Since the late 1950's, better residue management techniques have increased surface residue cover during fallow had increased fallow efficiencies on 16% to over 40%. Residue on the soil surface during fallow reduced evaporative losses, increased soil water storage, and increased deep percolation of soil water below the crop rooting depth. Therefore, the frequency and length of fallow in the future may be reduced by using greater crop intensity and diversity. This would result in cropping systems that are more sustainable.