Influence of soil physicochemical properties on urban market gardening performance in sarh (Chad)

Urban market gardening is making an increasingly significant contribution to food security and the livelihoods of urban populations in sub-Saharan Africa, but its performance remains heavily dependent on soil quality. This study analyses the influence of soil physico-chemical properties on the performance of urban market gardening in the town of Sarh, located in the Sudanese zone of southern Chad. Fifteen vegetable plots representative of the main production areas were sampled. The soils underwent physico-chemical analyses for pH, electrical conductivity, organic carbon, organic matter, total nitrogen and available phosphorus. Vegetable yields were estimated at the smallholder level using the density square method, then extrapolated to the hectare. The results show significant textural heterogeneity in the soils, characterised by a predominance of the sandy fraction (58.53 ± 10.84%), followed by clay (27.20 ± 7.99%) and silt (14.27 ± 5.15%). The soils have a slightly acidic to near-neutral pH (6.42 ± 0.38) and an average electrical conductivity of 185.1 ± 44.1 µS•cm⁻¹, indicating the absence of saline stress. The average organic carbon (3.22 ± 1.05%) and organic matter (5.54 ± 1.79%) contents are relatively high but spatially variable, as is total nitrogen (0.050 ± 0.018%). Estimated vegetable yields range from 9.5 to 15 t•ha⁻¹ depending on the site. Statistical analyses performed using R software reveal a strong and significant positive relationship between yield and organic carbon (r = 0.867; p < 0.001) and organic matter (r = 0.864; p < 0.001). Principal component analysis highlights a major organo-mineral fertility gradient contrasting organic matter-rich and more clayey soils, associated with higher yields, with less productive sandy soils. PH appears to be a factor that influences nutrient availability, though it is not the primary determinant of productivity. This study highlights the central role of organic matter management and soil structure in the sustainable improvement of urban market gardening in Sarh.