The study analyzed farm input productivity and estimated constant elasticity of substitution of fertilizer for manure for
vegetable farmers in the southern region of Nigeria. Primary data obtained from four hundred and eighty vegetable farmers in
Uyo and Itu regions of the southern part of Nigeria were used in the study. A combination of analytical tools including descriptive
statistics (percentages, frequency and tables), and regression analysis were used for data analysis. The generalized constant
elasticity of substitution function was specified and estimated through a system of coefficients relationship after which the
constant elasticity of substitution of fertilizer for manure for each crop enterprise was calculated. The empirical results revealed a
constant elasticity of substitution of fertilizer for manure of about 27.21% for waterleaf production and 35.11% for fluted pumpkin
production in the region. The Cobb-Douglas production function for waterleaf production revealed that planting material, family
labor, fertilizer, manure, and water have significant influenced on waterleaf production; while the linear production function for
fluted pumpkin production revealed that seed, hired labor, fertilizer, and manure have significant impact on the quantity of fluted
pumpkin produced. The result also revealed that the utilization of all significant production inputs of the two crop enterprises
were in the rational zone of the classical production surface. A mean total factor productivity of 45.60% and 45.59% were
realized for waterleaf and fluted pumpkin farms respectively in the region. The study however recommended that government
should increase fertilizer supply to vegetable farmer at a subsidized rate, intensify effort towards increasing research on manure
production to adequately complement the use of fertilizer and make land more accessible to vegetable crop farmers in the
region. Also, farmers cooperative organizations should be encourage among vegetable farmers as this would make inputs
acquisition less cumbersome.