THE ROLE OF NITROGEN-FIXING ENDOPHYTIC BACTERIA IN REDUCING NITROGEN FERTILIZER APPLICATION RATES AND ENHANCING MAIZE GROWTH ON KENTRONG ULTISOLS

Maize cultivation on Ultisols is constrained by low nitrogen availability. One strategy to improve nitrogen availability is the application of biofertilizers containing effective nitrogen-fixing bacteria. This study aimed to determine the best combination of nitrogen fertilizer application rate and biofertilizer application rate to enhance maize growth on Ultisols from Kentrong. The experiment was conducted in a greenhouse using a randomized block design consisting of 16 treatments with three replications. Treatments consisted of four urea fertilizer application rates (200, 160, 120, and 80 kg ha⁻¹) combined with different biofertilizer application rates and methods, namely 1.2 kg ha⁻¹ as seed coating, 2.4 kg ha⁻¹ as soil treatment, and 3.6 kg ha⁻¹ as a combination of seed coating and soil treatment. The results showed that the combination of urea fertilizer and biofertilizer application rates significantly affected endophytic bacterial populations in roots and leaves, plant fresh weight, root dry weight, leaf dry weight, plant height, stem diameter, nitrogen uptake, and nitrogen content, but did not significantly affect leaf number. The application of 80 kg ha⁻¹ urea fertilizer combined with 3.6 kg ha⁻¹ biofertilizer was identified as the optimal treatment for increasing maize dry biomass while reducing urea fertilizer application rate.