Long-Term Bacterial Fertilizer Application Improves Eucalyptus Growth and Yields through Altering Soil Quality

Sludge and plant growth-promoting rhizobacteria (PGPR) are widely used to improve soil quality and plant growth. In this study we aim to determine the responses of soil enzyme activities, soil nutrient contents and plant growth to fertilization with sludge and PGPR (Bacillus megaterium strain DU07). To achieve this goal, we planted bare-root eucalyptus seedlings with soil amended with (1) filtered sludge from sugar factory (FS), (2) filtered sludge + PGPR (BF) and (3) non-amended soil (control). Soil properties (soil nutrients and soil extracellular enzymatic activities) and eucalyptus growth (diameter, height and stem volume) were studied 3, 6, 9 and 12 months after treatments. Results indicated that BF significantly increased plant height, diameter, and stem volume after the sixth month. Principal component analysis (PCA) showed that soil quality was significantly increased by BF during our trial period, especially after the ninth month. The pooled regression model indicated that soil quality significantly and positively affected eucalyptus yield, whereas soil TN was negatively and significantly related to plant stem volume. Hence, our study indicates that the application of a bacterial fertilizer increases plant growth and yield via increasing soil quality. Thus, our findings suggest that PGPR amendments could be useful as bio-fertilizer to improve soil-plant interactions in eucalyptus plantations.