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.
The productivity of the Vertisols of the Accra plains is low, in spite of its high potential fertility. This could be attributed to physical constraints and low organic matter content. A study was conducted at the Agricultural Research Centre, Kpong, to assess the suitability of Mucuna pruriens, Mimosa invisa and Stylosanthes guianensis, in short fallows, for improving the fertility, physical properties, moisture conservation and weed control in the case of these soils. Mucuna had the highest biomass of 5.3tha 21 , as opposed to 4.1tha 21 under natural fallow. The mucuna and stylosanthes biomass had comparatively higher total N values (240.75 and 203.51kgha 21 , respectively) than mimosa and natural fallow (152.46 and 162.74kgha 21 , respectively). Soil organic carbon, one year after the incorporation of cover crops, was found to be relatively higher under the cover crops (mucuna, stylosanthes and mimosa) than it was under natural fallow. Bulk densities were thus lower under the cover crops than they were under natural fallow. Also, soils under the cover crops had higher total porosity, water infiltration rates and moisture storage than they did under natural fallow. Weed cover, 115 days after planting maize, was significantly lower in plots previously under Mucuna pruriens than it was under natural fallow, Stylosanthes guianensis and Mimosa invisa. There was a negative linear correlation between cover crop biomass and weed density (R 2 ¼ 0.593-0.805). Grain and stover yields of maize were higher under Mucuna pruriens than they were under natural fallow (138 and 70 per cent higher, respectively). Burning of the natural fallow resulted in greater weed growth than when the material was worked into the soil (41 and 8 per cent, respectively). Grain yield was significantly greater under mucuna than it was under natural fallow (3.1 and 1.3tha 21 , respectively).
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