Effects of biofertilizers on aggregate formation and stability of soil

In this study, the effects of five different biofertilizers (alone or in combination) on aggregate formation and stability of clay-loam (Typic Xerofluvent) textured soil, in which maize (Zea mays L.) plant was grown, were investigated. Moreover, the effects of treatments on organic carbon contents of macroaggregates of 2-1 mm diameter and microaggregates of 0.25-0.050 mm diameter were assessed and correlation between organic carbon content and aggregate stability was determined. The study was conducted as a pot experiment under greenhouse conditions using a Completely Randomized Design with three replications. The study consisted of eleven experimental treatments: control (no fertilizer) (K), inorganic fertilizer (15:15:15 compound fertilizer+ammonium nitrate, 33% N) (G), biofertilizer containing mycorrhizal fungi (Glomus spp.) (M), biofertilizer containing microalgae (Chlorella spp.) (A), biofertilizer containing bacteria (Bacillus megaterium KBA-10+Pantoea agglomerans RK-134 +Pseudomonas fluorescens FDG-37) (BMF), another biofertilizer containing bacteria (Bacillus subtilis PA1+Paenibacillus azotofixans PA2) (BCP), vermicompost (V), vermicompost+mycorrhizal fungi (VM), vermicompost+microalgae (VA), vermicompost+bacteria (VBMF), vermicompost+bacteria (VBCP). At the end of 90 days incubation period, the results of the study showed that biofertilizer treatments tended to increase the formation of macroaggregates. The amount of macroaggregates was significantly enhanced by treatments compared to control (respectively; >4 mm size class by BCP, 4-2 mm size class by M treatment, 2-1 mm size class by M, A and V treatments). The amount of aggregates >4 mm was greatly increased as a result of combined applications of biofertilizers and vermicompost. Vermicompost+mycorrhizal fungi (VM) statistically had the most significant increase on stability of macroaggregates of 2-1 mm size class. Likewise, it was observed that M treatment had an increasing impact on stability of macroaggregates (2-1 mm). Also, both of biofertilizers containing bacteria, alone or in combination with vermicompost, significantly improved stability of aggregates of macro (2-1 mm) and micro (0.25-0.050 mm) size classes compared to control. Biofertilizer treatments increased organic carbon content of macroaggregates of 2-1 mm diameter and microaggregates of 0.25-0.050 mm diameter both in general and at different levels. Besides that, it was determined that biofertilizers in combination with vermicompost mostly had stronger effects on organic carbon content of aggregates of macro (2-1 mm) and micro (0.25-0.050 mm) size classes in comparison with control and biofertilizer treatments alone. Vermicompost (V) treatment didn't have a significant effect on aggregate stability, whereas it significantly enhanced organic carbon content of aggregates of macro (2-1 mm) and micro (0.25-0.050 mm) size classes. The effect of inorganic fertilizer (G) treatment on aggregate stability or organic carbon content was not found significant for any aggregate sizes (2-1 mm or 0.25-0.050 mm). Significant and positive correlations between organic carbon contents and stability values of aggregates of macro (2-1 mm) and micro (0.25-0.050 mm) size classes that were obtained by each treatment at the end of the experiment were observed.