The biostimulatory effect of humic-based soil amendment on plant growth, root nodulation, symbiotic nitrogen fixation and yield of field pea (Pisum sativum L.)

Introduction

Pea is one of the most important pulse legumes globally due to its high protein, which is due to its ability to fix atmospheric nitrogen through a symbiotic relationship with nitrogen-fixing rhizobia. Symbiotic nitrogen fixation (SNF) should be optimized to maximize nitrogen fixation and achieve higher yields with more grain protein. The use of humic-based soil amendments in crop production has garnered considerable attention in recent years due to their biostimulatory effect in improving plant growth, yield, nutritional quality and soil health. This study examines the impact of a humic-based soil amendment (Humalite) on root nodulation, SNF, plant growth, yield and grain protein of pea.

Materials and Methods

Chemical characterization was performed using Fourier transform infrared spectroscopy (FTIR). Pea plants inoculated with Rhizobia were grown in pots under greenhouse conditions with five different Humalite rates (0, 200, 400, 800 and 1600 kg ha⁻¹). SNF capacity was assessed using the ¹⁵N-isotope dilution method.

Results

FTIR analysis revealed the abundant presence of hydroxyl (-OH) and carboxyl (-CO) functional groups in Humalite. Plants treated with Humalite displayed augmented root traits [root length (21%–50%), root surface area (24%–51%), volume (26%–53%), average nodule weight (11%–91%)], plant biomass [shoots (13%–29%) and roots (29%–54%)], shoot nitrogen concentration (12%–33%), shoot total nitrogen content (38%–53%), percentage nitrogen derived from the atmosphere (8%–14%) and total shoot nitrogen fixed (48%–80%) compared to the control plants at the flowering stage. Furthermore, at seed maturity stage, plants treated with Humalite at 400 and 1600 kg ha⁻¹ exhibited a significant increase in plant biomass (4%–14%), number of seeds (8%–16%), seed weight (3%–11%), seed nitrogen content (8%–20%) and total seed nitrogen fixed (7%–22%) compared to the control plants.

Conclusions

These findings demonstrate that humic-based soil amendment can effectively enhance plant growth, root nodulation, SNF and seed yield, thereby supporting sustainable agricultural practices.