Site-Specific Nutrient Management for Lowland Rice in the Northern Savannah Zones of Ghana

A multi-location study was conducted to assess the nitrogen (N), phosphorous (P) and potassium (K) requirements of lowland rice (Oryza sativa L.) for a local variety Digang cultivated in the northern Savannahs of Ghana and offer site specific nutrient recommendations. Ten on-farm nutrient omission trials involving five rates of N, P and K combinations were conducted during 2010 cropping season in Sudan and Guinea Savannah agro-ecological zones. The treatments (kg/ha as N, P2O5 and K2O) comprised 0-0-0 (control), 0-90-90 (zero N), 90-0-90 (zero P), 90-90-0 (zero K), 90-90-90 (NPK). Grain yields were increased by applying fertilizer N, P and K in sufficient amounts (90 N, 90 P2O5 and 90 K2O kg/ha) to overcome deficiencies and maintain soil fertility. Nitrogen was a major limiting nutrient in the irrigated and rain fed lowlands in the northern Savannahs of Ghana. The N-limited yields varied between 832 and 1875 kg/ha, suggesting variability of N supplying capacity of the experimental plots. The impact of omitting N was different among the locations with the irrigated lowlands ecosystems in the Sudan Savannah that recorded the highest yield loss due to N omission and Guinea Savannah the least. Higher level of fertilizer N (118 kg/ha) was required in the irrigated lowland in the Sudan Savannah to achieve maximum yield compared with 52 to 79 kg N/ha in the rain fed lowlands of Guinea Savannah. Potash fertilizers have little effect on yield, especially in irrigated lowlands in the Sudan Savannah. Grain yield reductions due to nutrient deficiencies were more severe in the Upper West region than in Upper East region and Northern region. Higher levels of N in irrigated lowland ecosystems in the Sudan Savannah and higher P and K may be required in Upper West region in the Guinea Savannah than recommended for achieving higher yields on a sustainable basis.