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Decline in crop yield has been a major problem in Northern Guinea savanna zones of Nigeria due to inherent low fertility status of the soils. Field experiments were conducted for two years (2003 and 2004) on an Alfisol of the Northern Guinea savanna of Nigeria to determine the effect of N fertilizer on growth and yield parameters of sunflower. Six rates of nitrogen (0, 30, 60, 90, 120 and 150 kg N ha-1) were applied. Plant height and number of leaves were highly significant 10 weeks after planting (WAP). Highest plant heights of 120 and 138 cm were obtained in 2003 and 2004, respectively, at 120 kg N ha-1. Application of N significantly increased seed and oil yields while excess N (150 kg N ha-1) reduced the contents of the two parameters. Optimum N requirement of sunflower obtained from this study is between 90 and 100 kg N ha-1 .

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Core Ideas Lowland irrigated rice is increasing in importance in West Africa.The irrigated lowland rice response to N was curvilinear to plateau.Irrigated lowland rice was inconsistently affected by applied P.A profitable rice response to K, Mg, S, Zn and B is not likely. Yield response of irrigated lowland rice (Oryza sativa L.) to nutrient application was determined to improve the information base for fertilizer use in the Sudan and Southern Guinea Savannas of Nigeria. Economically optimal rates (EOR) and agronomic efficiency (AE) were determined. Five N levels and four levels each P, K, and Zn were evaluated with two varieties at two locations. Nitrogen effects varied by variety and location but mean paddy yield with 0 kg ha−1 N was 3.4 Mg ha−1 and was increased by 1.3 Mg ha−1 with 40 kg ha−1 N. The mean EOR of N with fertilizer use cost to paddy price ratios (CP) of 2 to 6 were 56 to 38 kg ha−1 N, respectively. Yield increases with P, K and Zn application were infrequent. Paddy yield was increased in one of four cases with up to 1.5 kg ha−1 Zn. There were no paddy yield increases but some decreases with application of Mg‐S‐B in addition to N‐P‐K‐Zn. The overall AE of N at EOR with a CP of 4 was 25.3 kg kg−1. The profit potential of N application was greater for Faro 44 compared with Faro 52 at both locations. Financially constrained farmers who opt to apply N at 50 compared with 100% EOR when CP was 4 can expect 16% less yield increase but 67% higher AE and value to cost ratio. Application of fertilizer N, maybe with P at Kadawa, can be highly profitable for irrigated lowland rice in these agro‐ecological zones.