Abstract
Three separate field studies were conducted in a rainforest area to determine efficient use of applied fertilizers by maize and egusi-melon in various ratios of mixtures in an ultisol in Nigeria. The experiment was a factorial combination of seven cropping ratios of maize and egusi-melon (MA:EM 1:0, 1:1, 2:1, 3:1, 1:2, and 1:3, respectively) tested under four levels of NPK 20:10:10 (0, 200, 400, and 600 kg/ha) fertilizers replicated three timesfor two years as experiments 2009 and 2010, respectively. The fertilizer rates were increased by two levels (800 and 1000 kg/ha) in the third year as experiment 3 to validate earlier results of experiments 2009 and 2010. Efficient use of the applied fertilizers by maize and egusi-melon was determined in the 3 year study. Fertilizer use efficiency (FUE) was generally higher in experiments 2010 and 2011 than in 2009 and was also higher in sole cropping of maize and egusi-melon than their intercrop. The two crops efficiently used the applied fertilizers better with the lower rates (200 and 400 kg/ha) than the higher rate (600 kg/ha) in experiments 2009 and 2010, respectively. Even when the rates of the fertilizer were increased to 800 and 1000 kg/ha, respectively in experiment 3, FUE became progressively lower. Effectiveness of both crops with respect to FUE gradually declined with increasing levels of the fertilizer in all the trials. In intercrop, FUE was better for maize when intercropped with egusi-melon at 3:1 ratio than the other ratios in the three experiments. And for egusi-melon, FUE was best at the crop mixture of 1:2 in 2011. At each rate of the fertilizer, FUE of sole maize was similar to the value obtained for it in intercrop with egusi-melon at 3:1 ratio in all the experiments; FUE for sole egusi-melon at each fertilizer rate was significantly better (p<0.01) than the corresponding values from it in intercrop with maize in all the cropping ratios in each experiment. The implication of this finding is that egusi-melon is a poor competitor with maize for applied fertilizers and inherent soil nutrients while maize is a better competitor as its intercrop with egusi-melon had no adverse effect on its FUE when compared with sole maize. Key words: Fertilizer use efficiency,cropping ratios, Intercropping.  
Highlights
Intercropping system involving various crops and their rotations are common practices in the tropical and temperate regions for many reasons (Yamoah et al., 2003)
At each rate of the fertilizer, Fertilizer use efficiency (FUE) of sole maize was similar to the value obtained for it in intercrop with egusi-melon at 3:1 ratio in all the experiments; FUE for sole egusi-melon at each fertilizer rate was significantly better (p
The FUE of sole maize was similar to the value obtained for maize when it was intercropped with egusi-melon at the 3:1 ratio, whereas the FUE for sole egusi-melon at each fertilizer rate was significantly higher (p
Summary
Intercropping system involving various crops and their rotations are common practices in the tropical and temperate regions for many reasons (Yamoah et al., 2003). High and stable yields with enhance income are some of the reasons for the practice in Niger, Burkina Faso, while in the USA, it is used to reduce the levels of diseases and pests infestation. In Nigeria, it is used to avoid complete crop failure and reduce incidence of weeds, which are added reasons for the practice (Ehigiator, 1998). Growing crops in mixtures have been ascribed the benefit of improving yield of companion crops in intercrop (Yamoahet al., 2003) and have not received adequate research attention. Fertilizers recommendation is usually based on fertilizer need of the choice of one crop for the other(s) in intercrop; and not supported by any research data. Efficient use of the inorganic fertilizer by crops will be of advantage and profit to farmers
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