Long-term effects of tillage, sub-soiling, and profile strata on properties of a Vitric Andosol in the Kenyan highlands
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Tillage alters the structure and composition of soil aggregates affecting infiltration rate (IR) and hydraulic conductivity (K). This study investigated the long-term effects of conventional, minimum, and no-tillage with or without subsoiling on aggregate stability, soil organic carbon (SOC), bulk density, IR, and K of a stratified Vitric Andosol in Kenyan highlands. The experiment was laid out in a spilt-split plot design with three replicates. Stepwise profiles were dug in order to expose the soil layers at 0 to 30, 30 to 60, and 60 to 90 cm depths. Soil bulk density was 6% lower in the minimum tilled and 12% lower in the conventionally tilled plots that were subsoiled compared to treatments with no subsoiling and tillage. Subsoiled treatments also increased sequestration of SOC by 20% in the 30 to 60 cm layer. Conventional tillage, however, decreased aggregate stability by 32% compared to no-tillage treatments. Subsoiling in combination with minimum tillage decreased IR by 25% but increased IR about three-fold in conventionally tilled plots. Hydraulic conductivity in the 60 to 90 cm layer was lowest, which constrained water movement in this stratified soil.