Nitrogen Use Efficiency and Maize Productivity in the Guinea Savanna Agro-ecological Zone of Ghana

Blanket fertilizer recommendation for maize (Zea mays, L.) production in Ghana was made in the 1960s. Due to changes in soil fertility and for economic reasons, farmers are adopting different fertilizer rates and in various combinations to produce maize. The efficiency of the applications and effect on maize productivity have been rarely investigated. The objective of the study was therefore to investigate maize productivity and the nitrogen use efficiency of the current recommended fertilizer rate for maize production and other rates and combinations of synthetic and organic fertilizers being applied by farmers in the Guinea Savanna Agro-ecological Zone (GSAZ) of Ghana. On-farm research was conducted at five locations during 2014 and 2015 cropping seasons. The fields were laid out in a Randomized Complete Block Design with 16 treatments in three replications. The treatments consisted of the control (T1), eight synthetic fertilizer treatments alone (T2, T3, T4, T5, T10, T11, T12, and T13), six integrated treatments (T6, T7, T8, T9, T14, and T15), and T16 which involved the application of only Sulphate of Ammonia as top dressing. The combined application of poultry manure and synthetic fertilizer recorded significantly (P < 0.05) higher maize grain yields of 2.15 – 2.76 t/ha. Treatments that involved the combined application of synthetic fertilizers and poultry manure recorded the least Nitrogen Use Efficiency (NUE) values with T6 recording the lowest figure of 2.14±1.17. NUE was lower for synthetic + organic treatments because the total N was much higher for these treatments resulting in increased yields but at a decreasing rate. The NUE was significantly lower in 2015 than in 2014. Kanpong and Mognegu significantly (P < 0.05) recorded the highest (19.3±0.68) and lowest (4.27±0.75) NUE, respectively. Optimum maize grain yield can be obtained through the application of integrated nutrient management in the GSAZ of Ghana.