Morphology, Physico-chemical Characteristics, Nutritional Status and Fertility Capability Classification of the Benue Floodplain Vertisols in North Cameroon

Vertisols are one of the most fertile soils in the tropics but crop production is often limited by physical features related to shrink-swell movement under different moisture conditions making management strategies mostly tilted towards soil moisture control. However, most crops planted on vertisols often show signs of nutritional deficiencies whose causes are not yet fully understood. The main aim of the present work was therefore to characterize the vertisols of the Benue floodplain, to highlight some potential causes of nutritional deficiencies and to attempt a fertility suitability classification (FCC) of those soils. The work was done in the field and in the laboratory. The main results revealed that those soils, with a depth of 2-2.5 m above the water table, showed a dark grey color, a heavy clayey texture. Physico-chemically, they were characterized by high cation exchange capacity (CEC), high sum of exchangeable bases (S), high base saturation (S/T ratio), low organic carbon (OC), high total available phosphorus (TAP), low total nitrogen (TN) and high C/N ratio (10-26.5). The nitrogen­ versus pH equilibrium revealed that despite the suitable pH(H2O), close to neutrality, TN was deficient and limiting to plant growth. The Ca/Mg/K ratio revealed a cationic imbalance for Ca, Mg and K. The other equilibrium factors like potassium versus texture, sum of bases versus texture, CEC versus texture equilibrium and individual exchangeable bases versus CEC equilibrium revealed a very rich chemical fertility for the studied soils. Despite this richness, the heavy clayey texture and cationic imbalance of the different nutrients indicated limited nutritional uptake by plants, suggesting that management strategies for crop production on vertisols should not only be geared towards water management, but also towards nutrient balance.