The effect of agroforestry based conservation tillage on water infiltration and selected soil properties in southern Ethiopia

With the aim of evaluating the effects of agroforestry based conservation tillage (AFCT) on water infiltration and selected soil properties, two tillage types: Agroforestry based Conservation Tillage (AFCT) and Maize based Conventional Tillage (MCT) under three age categories (10, 20 and 30-years) were selected in Wonago District, Southern Ethiopia. A total of 48 composite soil samples (4 replication * 2 tillage types * 3 age categories * 2 soil depth layers: 0-20 cm and 20-40cm) were collected to analyse the soil organic carbon (SOC%) content of the soil together with soil textural fractions (%) and porosity (%). Additional undisturbed core samples were also collected to determine soil bulk density (g cm-3). Water infiltration capacity was measured in the field using double ring infiltrometer. From the three age categories, a total of 18 measurement points (3 replication * 2 tillage types * 3 age categories) were carried out for one full hour and changes in water levels were recorded at time increments of 1, 2, 5, 10, 15, 20, 30, 40 and 60 min for calculation of rate and cumulative water infiltration. The result showed that the soil textural fractions (sand, silt and clay) significantly varied (ρ<0.001, P<0.001 and P = 0.002, respectively) with age of land use management. Soil bulk density, Pt and SOC varied significantly with tillage types (ρ<0.001) and soil depth (ρ<0.001). Water infiltration (rate and cumulative) significantly varied (ρ< 0.001) with tillage types: higher in the AFCT than in the MCT. Lower soil bulk density and higher SOC were observed in the top 0-20 cm soil layer under the AFCT than in the MCT. Soil bulk density increased while Pt and SOC decreased with soil depth in both tillage types. Improvement in the water infiltration under AFCT was due to higher soil organic carbon (SOC) input and less soil disturbance. Thus, reducing the frequency of soil disturbance through application of agro forestry based conservation tillage would help to improve water infiltration capacity and other soil qualities.