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Title: Precipitation Storage Efficiency During Fallow in Wheat-Fallow Systems

Author
item Nielsen, David
item Vigil, Merle

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2009
Publication Date: 1/14/2010
Citation: Nielsen, D.C., Vigil, M.F. 2010. Precipitation Storage Efficiency During Fallow in Wheat-Fallow Systems. Agronomy Journal. v.102(2)537-543.

Interpretive Summary: Wheat-fallow systems are used to store water during the fallow period to stabilize yields from the wide year-to-year growing season variability. Precipitation storage efficiency during the fallow period increases as tillage used for weed control becomes less intensive or is totally eliminated (no-till systems). There are very large differences in previously reported precipitation storage efficiency values. Some very high values (>50%) have been reported for Akron, CO but not in other central Great Plains locations. This study compared PSE in conventionally tilled (CT) and no-till (NT) wheat-fallow systems over 10 seasons at Akron, CO against previously published values and attempted to identify meteorological conditions that may be influencing PSE. Over ten seasons, 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. PSE 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 greater than 25 mm can be used to accurately estimate PSE and fallow period water storage in this region.

Technical Abstract: Previously published values of average fallow precipitation storage efficiency (PSE) for Great Plains wheat (Triticum aestivum L.)-fallow production systems have ranged widely (10-53%). The objectives of this study were to compare PSE in conventionally tilled (CT) and no-till (NT) wheat-fallow systems over 10 seasons at Akron, CO against previously published values and to identify meteorological conditions that may be influencing PSE. Soil water measurements were made at four times during each fallow period to divide 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. 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. Fallow PSE was not different between the two systems during the second summer fallow period. 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. 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 greater than 25 mm can be used to accurately estimate PSE and fallow period water storage in this region.