Characteristics, Fertility Status and Fertility Capabiliy Classification of Vertisols along the Benue Floodplain (North Cameroon)

Vertisols are one of the most fertile soils in the World but crop production is often limited by physical
features related to shrink-swell movements under different moisture conditions making management
strategies mostly tilted towards soil moisture control. However, most crops grown on Vertisols often
show signs of nutritional deficiencies whose causes are not yet fully understood. The main aim of the
present work was to characterize the Vertisols of the Benue floodplain of North Cameroon, to highlight
some potential causes of nutritional deficiencies and to attempt a fertility capability 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, they showed a dark grey and a heavy
clayey texture. Physico-chemically, they showed a 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 moderate to high C/N ratio (10-27). The
nitrogen versus pH equilibrium revealed that despite the suitable pH(H2O), close to neutrality, TN was
potentially 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 good chemical fertility. The major constraints to crop production were heavy clayey
texture (C), waterlogging (g), organic matter depletion (m) and vertic properties (v), enabling the
Vertisols to be classified as Cgmv in the FCC system. Despite their high chemical fertility, heavy
clayey texture and cationic imbalance indicated a potentially 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 management. Thus, strategies to improve crop
production should include selection of appropriate crop varieties, introduction of suitable cropping
systems and chemical methods (right amounts and combination of nutrients).