Submitted to: Journal of Hydrology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2004
Publication Date: 3/1/2005
Citation: Gomez, J.A., Vanderlinen, K., Nearing, M.A. 2005. Spatial variability of surface roughness and hydraulic conductivity after disk tillage: implications for runoff variability. J. Hydrology. 311:143-156. Interpretive Summary: The infiltration of water into soil is highly variable in space and time. This has implications for scientists who are trying to understand hydrologic processes and the hydrologic cycle, as well as practical implications for farmers because infiltrated water is important for growth of crops and the water that does not infiltrate can cause erosion. This study attempts to understand how tillage operations can affect patterns of infiltration variations in the field. We measured infiltration on a freshly tilled field, then re-tilled the field and made the same measurements. We wanted to see if the patterns of infiltration were the same after the two tillage operations, and if the differences in the infiltration rates at points in the field could explain infiltration variability at the field scale. The results indicated that the variation of infiltration caused by tillage was not sufficient to explain the differences in infiltration that scientists observe in their data. The patterns of infiltration apparently were dominated by the compaction caused by wheels of the tractor and tillage implement that was used. Where the wheels passed, the soil was more compacted, and infiltration was restricted. We made some computer simulations which showed that the differences in the soils surface roughness was very important in explaining infiltration. Where soils are rough, a lot of the water that falls as rain can be trapped and held, giving it more time to be infiltrated. Where soils are smooth, the water can more easily run off the surface and cause erosion.
Technical Abstract: Hydraulic conductivity and surface roughness were measured twice on freshly tilled soil immediately after each of two disk tillages. The objective was to measure the modification in their spatial variability induced by consecutive tillage. One hundred and thirteen points were measured on a 1600-m2 area , each with a 1-m2 sampling area. The average values for roughness and field saturated hydraulic conductivity, Kfs, differed significantly after each tillage. This was attributed to the different soil conditions at the time of tillage. Both magnitudes showed some degree of spatial autocorrelation, mostly in the tillage direction, but no cross-correlation. Kfs showed a periodic behavior in the direction perpendicular to the tillage rows. The spatial distribution of surface roughness was completely different after two tillages made with the same equipment. The spatial distribution of Kfs after two tillages made with the same equipment were similar. An analysis with a runoff model suggests that the spatial modification of both magnitudes by tillage is not capable, alone, to explain the lack of stability of runoff in replicated plots. Simulations suggest that the lack of stability in runoff among replicated plots could be explained by the spatial modification of surface tillage combined with an infiltration dominated by a bimodal model of surface crusting regulated by microrelief.