2024, Vol. 7, Issue 9, Part J

author(s)
Naveena U, Triveni S, Bandeppa S and Ramanjaneyulu AV

abstract
Soil microorganisms play a crucial role in the biochemical and biological processes that govern soil health and sustain agricultural production. Among these microorganisms, plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that colonize plant roots and enhance plant growth through various mechanisms, including improving plant nutrition, producing and regulating phytohormones, and suppressing disease-causing organisms. Of the 52 isolates, 46 were unique in shape, colour, and margin, and were purified based on their morphological characteristics, followed by enumeration. Enumeration was conducted at three intervals in custardapple intercropped with fodder crops (Anjan and Guinea grasses), with the first interval yielding the highest CFU counts. This study demonstrates the significant impact of organic manures and nutrient management on microbial populations and crop yields in a custard apple-based intercropping system. Organic treatments, particularly T3 (75% RDN + 25% nitrogen through Pongamia green leaf manuring), resulted in the highest microbial counts (bacteria, fungi, and actinomycetes) in both Anjan (M1) and Guinea grass (M2). Bacterial populations were 120 × 10⁶ CFU g⁻¹ of soil in M1 Anjan grass and 140 × 10⁶ CFU g⁻¹ in M2 Guinea grass. Fungal populations were 35 × 10³ CFU g⁻¹ of soil in M1 Anjan grass and 30 × 10³ CFU g⁻¹ in M2 Guinea grass. Actinomycetes populations were 70 × 10³ CFU g⁻¹ of soil in M1 Anjan grass and 80 × 10³ CFU g⁻¹ in M2 Guinea grass. Guinea grass supported higher microbial activity, possibly due to favourable root exudates or soil interactions. In contrast, the lowest microbial populations were recorded in the control (T1) and 100% RDF (T2) treatments, underscoring the superior role of organic amendments in enhancing soil microbial diversity. Higher microbial populations in Guinea grass (M2) correlated with higher herbage (22.6 t/ha) and dry fodder yields (4.51 t/ha), while Anjan grass (M1) had lower yields (17.9 t/ha and 3.58 t/ha, respectively). Similarly, in custard apple, T7 (75% RDN + FYM) consistently yielded the highest bacterial (80 × 10⁶ CFU g⁻¹), fungal (33 × 10³ CFU g⁻¹), and actinomycetes (80 × 10³ CFU g⁻¹) populations, resulting in the highest fruit yield (6,842 kg/ha) and fruit number per tree (62). In contrast, the control (T1) had the lowest microbial counts and fruit yield (4,826 kg/ha). The findings emphasize the positive correlation between higher microbial populations and increased yields in both fodder and custard apple production.