Effects of conventional and conservation tillage on selected soil physical properties and water movement in a vitric andosol in Kenya

Abstract

Soil physical and hydraulic properties determine soil productivity. Tillage alters the structure and composition of a soil consequently influencing important soil processes such as water, air, heat flux, resistance to root penetration and nutrient availability. Soil layers have distinct physical properties which influence water movement in a profile. This study investigated long term effects of conventional, conservation and no tillage systems with or without initial subsoiling on some soil physical properties and water movement in a stratified vitric Andosol. The study was carried out at Menengai Feedlots Limited, a large-scale farm at Rongai area in Nakuru District, Kenya. The experimental layout was a split plot. The main factors were conventional tillage, conservation tillage and fallow land. The sub factors were initial subsoiling and no initial subsoiling. Stepwise profiles were dug in order to expose the soil horizons at three depths; 0-30 cm, 30-60 cm and 60-90 cm. Hydraulic conductivity and infiltration rates were determined in the field using tension infiltrometer. Soil texture, aggregate stability, organic carbon and bulk density were determined in the laboratory. The soil texture in 0-30 cm and 60-90 cm was loam. Organic carbon content decreased with soil depth in all tillage systems. The decrease was significantly drastic between 0-30 cm and 30-60 cm horizon but not between 30-60 cm and 60-90 cm. The pumice horizon (30-60 cm) of the initially sub-soiled treatments had significantly high organic carbon content (3.41%) compared to none initially sub-soiled treatments (2.48%). In 0-30 cm, Aggregates of 2-4 mm size were 90%, 80% and 58% for fallow land, conservation and conventional tillage, respectively. Conventional tillage had significantly low mean weight diameter compared to the other tillage systems. Initial subsoiling significantly increased bulk density and significantly decreased hydraulic conductivity and infiltration rate of 30-60 cm. Initial subsoiling therefore affected water movement of 30-60 cm most. Conservation tillage improved the soil physical properties compared to conventional tillage. A combination of initial sub-soiling followed by conservation tillage improved the soil physical and hydraulic properties of the vitric Andosols.