Rhizobia Inoculation Supplemented with Nitrogen Fertilization Enhances Root Nodulation, Productivity, and Nitrogen Dynamics in Soil and Black Gram (Vigna mungo (L.) Hepper)

Abstract

The potential interactions of rhizobium bacteria in enhancing nodulation, nitrogen (N) fixation for boosting N availability, and the yield of black gram under a temperate environment continue to remain unexplored. Therefore, this study aimed to evaluate the agronomic performance of black gram cultivars, their yield comparisons, and shoot–grain–soil N dynamics in a prevalently rainfed farming system. Two black gram cultivars, NARC Mash-I and NARC Mash-II, were subjected to rhizobia inoculation combined with different N doses (0, 25, 50, 75, 100 kg ha−1). The response variables included root nodulation, agronomic yield attributes, grain yield, shoot–grain and soil N dynamics, and biological productivity. Black gram cultivar NARC Mash-II showed the maximum nodule formation (41 per plant), while each nodule obtained 0.69 g weight in response to RI combined with 25 kg N ha−1. Additionally, this combination showed the highest pods per plant and thousand grain weight, which maximized the grain yield (1777 kg ha−1) and biological productivity (3007 kg ha−1). In contrast, NARC Mash-I under 50 kg N recorded the highest shoot N content, while the same cultivar under 100 kg N exhibited the maximum soil N content. The correlation analyses indicated a significantly robust association among the nodule numbers, grain weight, and N contents in different plant organs. These results give mechanistic insights into plant–microbe interactions based on the eco-friendly, sustainable, and smart agricultural practice of black gram production in a temperate environment.