Evaluation of Rhizobial Inoculation in Comparison to Urea Fertilizer Application of Vegetable Bean (Phaseolus vulgaris L)

Abstract

A field trial was conducted to evaluate the effects of Rhizobium inoculation in comparison to nitrogen fertilizer (NF) application on vegetable bean in the Ankumbura area, Kandy district during the Maha 2018/19 season. Six treatments were employed comprising four NF levels (55, 110, 165, and 220 kg urea/ha), rhizobium inoculation without NF, and control with neither NF nor inoculant. The treatments were set out in a randomized complete block design with three replicates. Four NF levels were 25%, 50%, 75%, and 100% of the recommended level for vegetable bean by the Department of Agriculture (DOA). All the treatments received potassium and phosphorous according to DOA recommendations. Pod yield/m2, growth parameters, several nodule parameters, and weed biomasses were recorded. Total yield (t/ha) was calculated based on the pod harvest. A yield versus fertilizer response curve was developed using calculated yield data. The highest total yield (3.03t/ha) with the application of 220kg/ha of urea was not significantly different from the yield produced under inoculation without NF (2.93 t/ha). This implies that inoculation facilitates a possible replacement of NF. Number of root nodules (30) and number of leaves (36) were significantly higher with inoculation. Higher levels; of 75% and 100% of recommended NF reduced nodule dry weight. Pod length, diameter, and dry weight with 100% and 75% NF levels were not significantly different (p<0.05) from those with inoculation. The highest pod N-yield (0.0586 g) and shoot N-yield (0.253 g) were recorded with inoculation and 220kg/ha urea application respectively. Weed biomass was significantly reduced (70%) with inoculation compared to the highest NF treatment. The results indicate a potential avenue to decrease the need for chemical nitrogen fertilizer and use inoculation to manage weed growth in vegetable beans in the Ankumbura area.