Fallow method influences on soil water and precipitation storage efficiency

Summer fallowing is practiced in the Great Plains of the U.S.A. in order to store soil water, control weeds, make nutrients available and stabilize crop yields. Soil water storage and precipitation storage efficiencies on chemical and stubble-mulch fallow plots were compared for three 14-month fallow periods for a winter-wheat-fallow rotation (Triticum aestivum L.) and three 21-month fallow periods for spring-wheat-fallow rotation in the northern Great Plains to determine during which seasonal segment the fallow method might influence soil water storage. The experiment was conducted on a glacial till Williams loam (fine-loamy mixed, Typic Argiboroll) from July 1981 to April 1985. Soil water contents to a depth of 1.70 m were measured, using the neutron scatter technique, for seasonal segments during the fallow period. Soil water storage was similar from harvest to spring on chemical and stubble-mulch fallow plots. The over-winter to spring segment resulted in the most consistent precipitation storage efficiencies (33.3–71.1%). Soil water storage differences as a result of a fallow method are most likely to occur during summer fallow for 14-month winter-wheat-fallow rotations and during the second overwinter for 21-month spring-wheat-fallow rotations. Soil water storage for the entire fallow period was greater on chemical fallow than on stubble-mulch fallow in two out of three 14-month winter-wheat fallow periods and in one out of three 21-month spring-wheat fallow periods.