Infiltration and soil moisture redistribution under freeze-thaw conditions

The availability and distribution of soil moisture within the mot zone is a key factor in ensuring better crop growth performance and attaining improved yield. The soil moisture is influenced by farm management practices such as cover cropping that affect the freeze-thaw processes during the fall. This in turn may influence accumulation and redistribution of soil moisture during the winter, and thereafter, the soil's response to thawing during spring, and availability of soil moisture for the subsequent season. The impact of cover cropping systems on soil temperature, infiltration, and soil moisture redistribution due to soil freezing and thawing was investigated. In addition, the effect of cover crop on the within-season and subsequent-season crop performance and yield was also investigated. Time Domain Reflectometry (TDR) and Neutron Scattering (NS) methods were used to measure the unfrozen and total water contents, respectively. Soil temperature was measured using thermocouples embedded in the soil profile. Soil moisture and soil temperature data were collected from August 2005 to September 2007.;During soil freeze-up, water from unfrozen soil layers below the freeze front migrated towards frozen layers above. Compared to non-cover crop treatment, the cover crop treatment did not freeze earlier during the fall, froze to a shallower depth during the winter, and accumulated less total water content in the mot zone by spring. This led to relatively wanner soil temperatures along the soil profile and earlier thawing during spring. During the growing season, the previously cover-cropped treatment had lower soil water content and poor crop growth performance that resulted in significantly lower yield of canola in 2006 (1.99 vs. 2.72 t ha-1). A physically based Simultaneous Heat and Water (SHAW) model was modified for use during wintertime to simulate hydrologic processes in soils experiencing seasonal soil freezing and thawing.;The depletion of soil moisture by the presence of cover crop can be beneficial to the main crop in wetter seasons. However, for drier seasons the cover crop will compete for soil moisture with the main crop resulting in negative effects. Rotational management practices that include cover crops need to consider using crops that are less sensitive to lower soil moisture during the subsequent season if it is expected to be drier.;Laboratory calibration of the TDR miniprobes indicated the maximum cable length for the RG-58 50 O coaxial cable to be 40.0 m when 35 mm TDR miniprobes were used. Since the TDR was found to overestimate the liquid water content at soil temperatures below 25°C, a method to correct the field measured TDR soil moisture for temperature effects was developed.