Studies were conducted at the Agricultural Research Centre, Kpong, of the University of Ghana, to find solution to the problem of low rice yields on the Vertisols of the Accra Plains. Rice yields from continuously cropped fields have been observed to decline with time, even with the application of recommended levels of inorganic fertilizers. The decline in yield has been attributed to low inherent soil fertility, which is partly the result of low levels of soil organic matter (OM). As part of the study, cow dung (CD) and poultry manure (PM) were separately applied to the soil at 20 t ha -1 solely and also 5, 10 and 15 t ha , on the Vertisols of the Accra Plains. Studies were also conducted on the redox potential of CD, PM and rice straw (RS). The application of 10 t ha -1 CD and urea fertilizer (at 45 kg N ha -1 ) and 10 t ha -1 PM and urea (at 60 kg N ha -1 ) both gave paddy yields of 4.7 t ha -1 , which did not differ significantly from the yield of 5.3 t ha -1 , obtained under the recommended inorganic nitrogen fertilizer application of 90 kg N ha -1 . This indicates a synergistic effect of OM and urea on soil fertility. The redox potential studies showed that RS had greater propensity to bring about reduced soil condition in paddy fields than CD and PM, while PM brought about greater reduction than CD.

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This chapter provides the geographical location of the Vertisols and vegetation types of the Accra Plains of Ghana. The agricultural importance and the socioeconomic characteristics of the regions are discussed. Recent interventions for improving the productivity of Vertisols, such as landform technologies, tiller services and tillage timing, use of improved seeds, chemical weed control, use of pesticides, improved cropping systems and fertilizer applications are discussed. Finally, different social and economic factors affecting Vertisol productivity in the Accra Plains are discussed.

The Vertisols of the Accra Plains of Ghana are water logged after significant rainfall due to the low-lying topography (0.1-1 %). Camber bed (Cb) drainage landforms have been developed at the Agricultural Research Centre, Kpong, for draining off excess water. Field experiments were conducted to verify if maize growth and yield gradient from the trough to the crest were the result of nutrient gradient or some other factors. Four 5 m and two 10 m Cbs and a 20-m flatland were prepared in a split-split plot design, with landform as main plot, nutrient levels as sub plot and crop row as sub-sub plot. A pot experiment was also carried out for detailed studies. Soil movement brought about a nutrient gradient from the trough of the camber bed to the crest, and also made the soil profile homogeneous. The trough was low in nutrients, compact and prone to water logging, but nutrient levels increased through the middle slope to the crest. The flatland did not have a nutrient gradient but was prone to water logging due to its low-lying nature. Total dry matter (TDM) of maize and grain yield similarly increased from the trough to the crest. Grain yield of maize on the flatland ranged from 2.5-2.6 t ha -1 , while yields on the 5-m Cb were 3.6, 4.2 and 4.8 t ha -1 on the trough, middle slope and crest, respectively. Excess application of 15-15-15 NPK and sulphate of ammonia fertilizers (150% of recommended levels) did not appreciably increase biomass and grain yield in the troughs. However, the maize crop in pots, with soil from the trough, responded positively to fertilizer application, thus confirming that low yield in the trough was the result of both low nutrient availability and the compact subsoil.

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