Enhancing root nodulation and boosting soil nitrogen mineralisation through strategic incorporation of sunnhemp as a green manure

Context Sunnhemp (Crotalaria juncea) is a highly valuable fast-growing subtropical legume crop that has potential as an effective green manure. Aim This study quantified nitrogen fixation in the sunnhemp–Rhizobium leguminosarum symbiosis and its effect on soil fertility at via green manuring plant biomass at different stages of growth. Methods Field experiments were established to assess the effect of inoculated and uninocuated sunnhemp biomass production on soil properties, N fixation, and rate of N mineralisation over time. Key results Our results showed that the bacteria isolated from sunnhemp root nodules had highly efficient nodulation capabilities. After inoculation of sunnhemp seeds, these bacteria efficiently fixed atmospheric nitrogen and enhanced overall plant growth and productivity. Furthermore, the production of green biomass from sunnhemp was significantly influenced by the plant growth stages, with a notable 44% rise in fresh weight observed between 30 and 50 days after plant emergence. Incorporating sunnhemp green manures at different growth stages was also shown to increase the available nitrogen status of the soil up to 37.94%, with a higher percentage (42–48%) of ammonium nitrogen over control. Conclusion By optimising the timing of green manure incorporation, farmers can harness the full potential of this renewable nitrogen source to fulfil about 40–50% of the nitrogen demands of the succeeding crop under an integrated nutrient management system, thereby boosting agricultural productivity and sustainability. Implications The practice of growing sunnhemp as a green manure exemplifies the principles of regenerative agriculture in action.