Combined effect of municipal sewage sludge and inorganic fertilizers on marketable pod yield of vegetable cowpea in sandy regosol soil

Vegetable cowpea (Vigna unguiculata L.) is one of the leguminous crops which can fix atmospheric nitrogen to improve soil nutrients. For obtaining high crop yield, fertilizers are applied effectively to provide the required plant nutrients with minimizing environmental problems. This study was conducted to determine the combined effect of municipal sewage sludge and inorganic fertilizers on pod yield of vegetable cowpea. The eight treatments were designed in a Completely Randomized Design with five replicates. Treatments included T1- no fertilizer, T2- 100% inorganic fertilizers (urea, TSP, MOP), T3- 10 t/ha sewage sludge alone, T4 - 20 t/ha sewage sludge alone, T5- 10 t/ha sewage sludge + 50% inorganic fertilizers (TSP, MOP), T6- 20 t/ha sewage sludge + 50% inorganic fertilizers (TSP, MOP), T7- 10 t/ha sewage sludge + 100% inorganic fertilizers (TSP, MOP), T8- 20 t/ha sewage sludge + 100% inorganic fertilizers (TSP, MOP). One- way Analysis of variance test was used to determine the significance level of the treatments. The results confirmed that sewage sludge with phosphorous and potassium inorganic fertilizers had significant differences (P<0.05) 

in yield parameters. According to the statistically analyzed results, 20 t/ha sewage sludge with 100% TSP and 100% MOP treatment (T8) showed the best treatment for the yield of vegetable cowpea in terms of marketable pod yield. But T5 (10 t/ha sewage sludge + 50% TSP + 50% MOP) and T8 (20 t/ha sewage sludge + 100% TSP + 100% MOP) did not show a significant difference of marketable pod yield produced (1029.83 g/m² and 1221.17 g/m² respectively). Based on the results of this study, it can be concluded that combined application of 10 t/ha sewage sludge with 50% phosphorous and potassium inorganic fertilizers could be used for environmentally friendly manner cultivation of vegetable cowpea in sandy regosol soil conditions.