Abstract:
The use of manures, inorganic fertilizers and leguminous crops has been advocated to restore the lost
nutrients in soils. Biological nitrogen fixation is considered as an important trait of cowpea for economic
production. Yet the process alone does not provide the quantity of nitrogen required by the plant for
maximum productivity. A pot experiment was carried out to investigate the effects of combined use of
organic manure and inorganic fertilizer on nitrogen fixation of vegetable cowpea grown in sandy regosol.
This experiment was laid out in a Completely Randomized Design (CRD) with seven treatments and three
replicates. Gliricidia, ipil ipil, paddy straw, poultry manure, cattle manure and goat manure were
evaluated with recommended level of inorganic fertilizer. Among the different types of organic manure
combinations with inorganic fertilizer, highest nodulation was obtained in sole application of inorganic
fertilizer while lowest nodulation but high nitrogen in soil was in poultry manure combination. This
confirms that legumes will obtain less of their nitrogen requirement from the atmosphere if there is an
adequate supply of nitrogen available from the soil. In addition, the results revealed that among plant
residues straw was inferior to ipil ipil and gliricidia as a source of organic manure for vegetable cowpea
production. Therefore, the combined use of poultry manure with inorganic fertilizer can be recognized
and can be suggested to the farmers as the most suitable way for ensuring the high crop yield of cowpea
on sandy regosol in order to maximize the nitrogen uptake. The second best source is ipil ipil manure and
inorganic fertilizer combination.
