Green waste biochar and plant growth-promoting bacteria enhance tomato growth under combined nutrient deficiency and salinity stress

This study characterized a green-waste-derived biochar from date palms and ghaf trees and investigated its potential as a soil amendment with halotolerant Bacillus spp. to improve tomato seedling quality under dual stress of salinity and nutrient deficiency. Biochar was produced through pyrolysis at 450 °C and then characterized for yield, pH, electrical conductivity, proximate analysis, surface morphology, energy-dispersive X-ray spectroscopy, and heavy-metal content. Its effectiveness was tested both alone and in combination with a Bacillus sp. mix, using a completely randomized design with varying NPK fertilizer levels and saline irrigation. Tomato seedlings were evaluated 45 days after planting for various vegetative, morphological, physiological, and nutrient content indicators. Under normal conditions, applying biochar combined with a Bacillus mix at 0% NPK greatly enhanced all measured parameters, often exceeding values observed with 100% NPK fertilization. This approach was especially effective under saline irrigation, resulting in significant increases in morphological parameters (40-150%), physiological parameters (51-94%), and nutrient content (34-63%) compared to control plants that received 100% NPK. Additionally, this treatment resulted in a 42% decrease in sodium accumulation. Using the biochar with the Bacillus mix effectively replaces chemical fertilizers and enhances salinity tolerance, supporting sustainable farming through waste recycling and less dependence on fertilizers.