Soil properties after change to conservation agriculture from ridge tillage in sandy clay loams of mid-altitude Central Malawi

A comparative study was carried out of annual ridge tillage (RT) and short-term effects of conservation agriculture (CA) on soil properties in fields of small-scale farmers. Soil samples were collected at depths of 0–10 and 10–20 cm from a total of 12 fields which had been under CA for two and four seasons, respectively, and from adjacent RT fields for direct comparisons. CA fields were converted from fields previously under continuous RT. Soil organic carbon, total nitrogen and available phosphorus were greater in CA fields while extractable potassium, pH and salt content were moderated under CA. Conversion of long-term RT to CA did not significantly influence bulk density and aggregate stability (geometric mean diameter) although structural stability was greater under CA practices. Total porosity, macroporosity and matrix porosity, and volumetric water content at saturation, field capacity and permanent wilting point did not substantively respond to tillage effects. Relative water capacity and air–water storage parameter, hfc/PORt, were significantly greater after 4 yr of CA. Soils under CA showed greater values for field-saturated hydraulic conductivity compared with RT fields. With the highest loadings in a principal component analysis, this work suggests that variables related to volumetric water content and aeration of the soil matrix, organic carbon, available phosphorus and soil texture were the most useful indices for future field comparison of RT and CA practices