Effect of sugarcane residue retention and fertiliser application on soil microbial abundance and community structure

This study, carried out in a long-term sugarcane trial, investigated changes in selected soil microbiological properties induced by continuous crop residue burning or mulching, with and without fertiliser application. The sugarcane residue treatments are: a) burned with tops removed (Bto); b) burned with tops scattered (Bt); and c) green harvested and mulched (M). These treatments were either fertilised (F) or unfertilised (Fo). The amount of double stranded deoxyribonucleic acid (dsDNA), used in this study as an indicator of soil microbial biomass, increased with increasing crop residue levels (Bto: 10.4 mu g g(-1): 12.2 mu g g(-1) M: 14.4 mu g g(-1)) in Fo treatments, suggesting that high soil organic matter levels in M treatments serves as the major energy and carbon source for microorganisms. However, significant differences (p<0.01) were only observed between Bto and M treatments. In F treatments the dsDNA amount was similar across all crop residue treatments but significantly (p<0.01) lower than in Fo plots. The significantly low dsDNA amount found in the F treatment was attributed to high soil acidity levels measured in this treatment compared with Fo. In both Fo and F plots, M treatments significantly (p<0.01) increased in the bacterial abundance. In contrast, the M treatment showed a significant (p<0.01) decrease in fungal abundance in comparison with Bto and Bt. Bacterial and fungal richness increased with increase in crop residues and decreased with fertiliser application. These results highlight the value of greencane harvesting and the negative impact of continuous blanket application of fertiliser on soil quality.