Filling an ephemeral gully channel: Impacts on physical soil quality

Soil erosion by water remains a major problem in many regions of the world and in many cases the dominant source of sediment is from gully erosion. Filling-in ephemeral gullies by mechanical operations serves to maintain high erosion rates and degrades the soil from areas used for filling, however, the impact of gully filling on soil quality is uncertain. The objective was to quantify the impact of filling of an ephemeral gully on crop yield and soil quality adjacent to the gully. An ephemeral gully was sampled for in situ physical (topsoil depth, soil color, shear strength, soil penetration resistance) properties and hydraulic (bulk density, saturated hydraulic conductivity, water retention) properties from undisturbed cores in a field in the sixth consecutive year of No Till. The field was selectively resampled the following year immediately following tillage. Soil properties were measured and sampled every 7.6 m out to 37 m from each side of the gully center along five transects perpendicular to the gully and a similar transect removed from the gully to represent baseline conditions. Filling of the gully by scraping soil from upper convex slope positions significantly reduced corn yield. The best indicators of soil physical quality were depth of topsoil, shear strength at the surface, and soil penetration resistance at the 5 cm depth and the best hydraulic properties were saturated hydraulic conductivity and several water retention characteristics. However, the slope of the retention curve at its inflection point was not found to be an indicator of soil physical quality. Every 1 cm loss of topsoil resulted in a 3.3 to 6.5% loss in yield. The soil physical quality indicators were dramatically changed by tillage such that the index developed was no longer appropriate. Future efforts need to address the dynamic changes in the soil quality index following tillage due to reconsolidation of the soil and whether inclusion of chemical and biological indicators would be less impacted by tillage.