Precipitation storage efficiency during fallow in wheat-fallow systems

Precipitation storage efficiency (PSE) is the fraction of precipitation received in a given time period that is stored in the soil. Average fallow PSE for Great Plains wheat (Triticum aestivum L.)-fallow (W-F) production systems have ranged widely (10-53%). Study objectives were to compare PSE in conventionally tilled (CT) and no-till (NT) W-F systems over 10 seasons at Akron, CO, against published values and to identify meteorological conditions that may influence PSE. Soil water measurements were made four times during each fallow period, dividing the fallow season into three periods (first summer, fall-winter-spring, second summer). Precipitation was measured in the plot area and other meteorological conditions were measured at a nearby weather station. The 14-mo fallow PSE averaged 20% (range 8-34%) for CT and 35% (range 20-51%) for NT, much lower than previously reported for NT at Akron. During the second summer period, PSE was not different between the two systems. The largest PSE difference between the two systems was seen during the fall—winter—spring period (32 vs. 81%). Fallow soil water increased an average of 111 mm under CT and 188 mm under NT. The PSE during the three fallow periods was related to tillage, precipitation, air temperature, vapor pressure deficit, and wind speed, but sometimes counter-intuitively. A simple linear regression using inputs of tillage system, percentage of fallow precipitation events with amounts between 5 and 15 mm, and percentage of fallow precipitation events with amounts > 25 mm can be used to estimate PSE and fallow period water storage.