3. Integrated Organic-Inorganic Fertilizer Management for Rice Production on the Vertisols of the Accra Plains of Ghana

Abstract

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^-1, in combination with urea fertilizer at 90, 60 and 30 kg N ha^-1, respectively. Other treatments included a control and urea fertilizer at 30, 60, 90 and 120 kg N ha^-1. There was a basal application of phosphorus and potassium to all plots at 45 kg P₂O₅ ha^-1 and 35 kg K₂O ha^-1, respectively, based on the recommended fertilizer rate of 90 kg N ha^-1, 45 kg P₂O₅ ha^{- 1} and 35 kg K₂O ha^-1, 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.