Bacillus PGPR consortium as a partial substitute for poultry litter improves forage performance in annual ryegrass and tall fescue under greenhouse conditions

Abstract Excessive poultry litter (PL) application in forage systems poses environmental risks. This study evaluated the potential of plant growth-promoting rhizobacteria (PGPR) to reduce PL dependence in annual ryegrass ( Lolium multiflorum ) and tall fescue ( Lolium arundinaceum ) production. Four PL rates (0%, 50%, 75%, 100% of 168 kg N/ha) were tested with and without a bacillus-based PGPR consortium ( B. altitudinis AP18, B. subtilis AP278, B. safensis AP280, and Lysinibacillus macroides AP282) in a randomized complete block design with six replicates. PGPR had no significant effect on seedling emergence but significantly enhanced plant height, tiller number, shoot and root biomass, and root traits across PL rates. These impacts were more pronounced in annual ryegrass. Ryegrass under 50% and 75% PL + PGPR was 3.8% and 8.66% taller than 100% PL alone. Tall fescue under 75% PL + PGPR was 2.84% taller than 100% PL, while 50% PL was slightly shorter but not significant. Tiller numbers under 50–75% PL + PGPR matched those of 100% PL in both grasses. Shoot biomass at 50% and 75% PL + PGPR in ryegrass (2.23 and 2.18 g/container) and tall fescue (1.08 and 0.44 g/container) was similar to 100% PL (2.02 and 0.44 g/container). PGPR at 50–75% PL increased root biomass by 10–12% in ryegrass and 4–17% in tall fescue. Additionally, 50–75% PL + PGPR improved root traits in the 0.51–2.00 mm and > 2 mm diameter classes compared to 100% PL. PGPR with reduced PL supports sustainable forage production.