Abstract
Roots of weeds that are left behind in the soil after removal of their aerial parts can reduce the growth of crops. Here we conducted an assessment to evaluate the allelopathic interference of Nicotiana plumbaginifolia roots and its rhizosphere soil on the growth of Pisum sativum L., identification of chemicals involved, the role of charcoal, the role of N and other macronutrients. Growth responses of P. sativum were analysed for (a) rhizosphere soil with and without N supplementation and (b) soil amendment with Nicotiana roots. Scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) analysis of the rhizosphere soil was conducted to look for concentration of essential nutrients. Rhizosphere soil showed an inhibitory effect even with N supplementation. SEM-EDS showed a healthy concentration of essential nutrients. Root residues of Nicotiana integrated with soil do cause a reduction in seedling length (root length, shoot length) and dry biomass of recipient plant. However, a partial alleviation in growth inhibition occurred upon the addition of activated charcoal. Soils amended with root residues were rich in phenolics as compared to control. Overall, 34 compounds were reported upon GC-MS analysis which can be considered responsible for the allelopathic suppression of P. sativum. The chief component was guanosine (26.21%) followed by n-hexadecanoic acid (18.61%), oleic acid (18.29%), palmitoleic acid (4.80%), -(-)nicotine (5.09%) and solasodine (2.54%). These results show a definite role of putative allelochemicals that exerted allelopathic effects on P. sativum.