Which one of the following crops enriches the nitrogen content in soil?
Pisum sativum, the common pea Because It is a nitrogen-fixing plant containing nodules on its roots. In this nodules, the biologically Nitrogen-fixing bacteria named Rhizobium spp. fixes nitrogen and is used by the plant. And also helps soil to be get enriched with it. Among the options mentioned in the question, only the pea increases the natural nitrogen contents in the soil where the pea plant is growing. So the correct option is D.