Surface Compost Effect on Hydrology: In-Situ and Soil Cores

ABSTRACT

Compost increases water-holding capacity and total porosity. Improved soil structure may increase volume of macropores, allowing better drainage, air-exchange, and root growth. The purpose of this study was to compare water retention curves and hydraulic conductivity for packed columns with and without additions of surface compost. Columns packed with subsoil (around 60 cm long) had either compost or topsoil added to the surface. Tensiometers and hydra probes monitored soil pressure head and water content during three wetting and evaporation cycles. The columns with compost had significantly smaller bulk density at the surface than columns with topsoil (0.87 versus 1.34 g cm⁻³). Surface compost amendment resulted in more water when satiated (0.617 versus 0.422 m³ m⁻³) and at −100 cm head (0.377 versus 0.276 m³ m⁻³) than for topsoil at the surface, indicating a greater fraction of larger pores for the compost amended. Whole column infiltration rate was significantly faster for columns with compost than without (1.46 versus 1.11 cm min⁻¹); however, saturated hydraulic conductivity (rate water flows through soil) on soil cores was not significantly affected by compost. Subsoil water flow and drainage was not significantly affected by surface compost. For the subsoil, in-situ column drying was significantly drier than core drainage at the wet end. There were no significant differences in whole column or surface water retention or evaporation rate. Perhaps the trend towards better water-holding capacity in the compost treatment was offset by larger pores and faster drainage, resulting in no significant difference between compost and topsoil.

ACKNOWLEDGMENTS

Mention of equipment manufacture is for information only and does not constitute endorsement by the USDA-ARS nor exclusion of similar equipment by other manufacturers. Many thanks to Gavin Simmons for data collection.