Influence of selected soil properties, soil management practices and socio-economic variables on relative weed density in a hand hoe-based conservation agriculture system

Weeds are problematic to the smallholder farmers, who practise conservation agriculture (CA) in sub-Saharan Africa, owing to an apparent lack of appropriate weed management strategies. We investigated weed dynamics under the planting basin (PB) system (hand hoe-based CA) to assist the design of appropriate weed management options. On-farm experiments were conducted under semi-arid conditions in Zimbabwe to determine the effects of 11 selected soil properties, four socioeconomic variables and two soil management practices on relative weed density. Weed counts were made according to species at 3, 6 and 9 weeks after crop emergence. Multivariate ordination techniques and a quadratic model, developed with partial least squares, showed that Richardia scabra increased with sand content in the soil. Density of R. scabra and Melinis repens also increased with topsoil potassium content. When ranked according to importance, relative weed density was most dependent on sand content followed by topsoil potassium, nitrate, clay and silt content, and training related to crop production. Soil physico-chemical properties, therefore, had greater influence on relative weed density than socio-economic variables and soil management practices. We concluded that variability in weed density under the PB system was not necessarily determined by tillage alone, but was also a consequence of soil properties and to a lesser extent of socio-economic variables and soil management practices. Understanding soil properties and management practices, which determine weed variability, helps in the design of general weed management recommendations that can be used by smallholders, most of whom do not have access to field-specific advice.