Crop Residue Effects On Surface Soil Sorptivity within Dryland No-till Management.

Soil physical properties such as bulk density, porosity, and aggregation dictate the water infiltration characteristics of the soil.  Most important are the physical properties of the surface soil as this layer is the initial soil-water interface.  Crop residue and tillage management may affect surface soil physical properties important to water capture and infiltration.  Management practices that minimally disturb the soil and produce, return, and leave more residue biomass on the soil surface have the potential to decrease soil bulk density and increase porosity in the soil over time.  A study was conducted to determine the effects of crop residue and soil physical properties on soil water sorptivity after 12 years of dryland no-till cropping management in eastern Colorado.  Sorptivity is defined as the cumulative infiltration proportionality constant and is essentially a measure of the amount time it takes a given head of water to infiltrate.  Sorptivity measurements were collected across soil catenas at three locations in eastern Colorado.  Each soil position and site location had differing amounts of crop residue returned to the soil over a 12 year period.  Crop residue amounts and soil physical properties were then related to the measured sorptivity at each location.  Results show that 77% of the variability in sorptivity measurements can be explained by soil bulk density and soil porosity.  Soil macroaggregation explained 72% of the variability in soil sorptivity, and macroaggregate organic carbon content explained 85% of the variability in sorptivity.  Overall, systems that resulted in more crop residue being returned to the soil also produced the highest sorptivity values and, therefore, had the highest potential for water capture.