Abstract
Six experiments covering the various climatic and ecological zone and soil type in Western Nigeria were used to assess the effects of Mg applied at rates of up to 60 kg/ha on earleaf composition and yield of maize. No yield response to Mg was obtained at any site but there was a fairly consistent trend in Mg uptake, particularly in the savanna areas. Magnesium in the earleaves at silking ranged from 0·18 per cent in the control plot to 0·41 per cent when Mg was applied at 60 kg/ha. Percentage Mg in the leaf was used as a measure of Mg availability and it was shown that Mg uptake was lower at exchangeable Mg/K ratio below 2. Extrapolation of these results based on earlier findings, however, indicated that yields might not be affected until this ratio falls below 0·8 or when the exchange able Mg level is below about 0·4 mequiv./100 g. Response to Mg in the forest areas of Western Nigeria is unlikely in the immediate future but Mg deficiencies in the savanna areas seem imminent. The onset of these deficiencies could be monitored through routine soil testing.
