Field experiments were conducted in 2007 and 2008 on
sandy loam soil in Guinea savanna of Ghana to evaluate sorghum (Sorghum
bicolor (L.) Moench) response to plant density and Nitrogen (N) fertilizer.
A randomized complete block design, arranged in a split-plot was used
with three replications. Four N levels (0, 40, 80 and 120 kg ha-1)
and plant densities (53300, 88800, 66600 and 133300 plants ha-1)
were assigned to subplots and main plots, respectively. Plant density
and N levels showed no significant interactions for any parameter. Further,
plant density had minimal effect on grain yield and yield components.
However, grain yield had a quadratic response to N levels. Across years,
application of 40, 80 and 120 kg N ha-1 resulted in yield increases
of 39, 43 and 45% over farmers practice (0 kg N ha-1),
respectively. Marginal Rate of Return (MRR) to 40 kg N ha-1
over the years was 281%, but negative to 80 and 120 kg N ha-1.
Increasing N level beyond 40 kg ha-1 did not result in corresponding
increase in yield, net benefit nor N use efficiency to merit the extra
production cost that may be incurred. From the study, application of 40
kg N ha-1 appeared adequate for maximizing sorghum yields,
regardless of plant density.