Combined application of humic substances and PGPR inoculated and co-inoculated in plants of Phaseolus lunatus (L.) and Leucaena leucocephala (Lam.) de Wit

Abstract

The objective of this research was to evaluate the effect of inoculation and co-inoculation of rhizobia and Azospirillum brasilense combined with humic substances (HS) in growth promotion of Phaseolus lunatus (lima bean) and Leucaena leucocephala (leucaena). For this, experiments in a greenhouse with the cultivation of each plant species were carried out. A randomized complete block experimental design with five repetitions was followed. Plant seeds were sown and then inoculated with rhizobia and co-inoculated with A. brasilense. Subsequently, HS were added at the dose recommended by the manufacturer. In the experiments with both plants, control treatments with the addition of nitrogen (N) with or without HS were used. After 45 days, the shoot dry mass (SDM), root dry mass (RDM), shoot-accumulated N (Nac) and relative efficiency index (REI) were determined. In addition, the mass of dry nodules (MDN) in the lima bean plants and the number of nodules (NN) in leucaena plants were determined. The results showed that in the lima bean and leucaena plants there was a greater increase in SDM, RDM and Nac in treatments that received HS and co-inoculation with rhizobia and A. brasilense than in treatments that were inoculated only with rhizobia and HS and in treatments that received N and HS compared to addition of N and isolated inoculation of rhizobia. The combined application of HS and rhizobia in co-inoculation with A. brasilense had a greater effect on the increase of MDN in lima bean and NN in leucaena, than in treatments where only rhizobia with HS were added. These results indicate the existence of potential interaction of the use of HS with the co-inoculation of rhizobia and A. brasilense, showing promise for the production of sustainable agricultural crops.