ABSTRACT

This study was conducted to evaluate and analyze the short term impacts of replacing mineral by organic fertilizers on the soil microbial and biochemical parameters relevant for soil fertility and crop yield. The experiment was set up as a randomized block design at the experimental field of the NRCRI Umudike, in 2016 planting season. Sweet Potato cultivar was used as the test plant. Four types of fertilization regimes were compared as treatments: Nitrogen Phosphorous potassium (NPK) fertilizer, Poultry manure (PM), Lime (LM) and combination of mineral and organic (NPK+PM+LM), non-fertilized (Control). Soil samples were collected before and after treatments at monthly intervals for 3 months. Soil physicochemical properties were carried out according to Duncan New Multiple Range Test's (DNMRT) at pO.O5. Cultural morphology and biochemical identification were carried out using standard microbiological techniques, and further confirmed through molecular characterization and identification. Results obtained showed that microbial count in untreated soil was low compared to treated soil. Bacterial count records that Poultry manure (PM) induced the highest population of 11 8.33x1 06±2.51 CFU/g among other treatment throughout the sampling period, followed by NPK 104.33x10±2.88 and treatment combination (NPK+PM+LM) 101.00x106±2.00 and Lime (LM) gave 73.33x106±2.51CFUIg as the lowest, Similar effect was seen on fungal counts which PM gave the highest of 17.00x103±1.73, followed by NPK, NPK+PM+LM and significantly reduced with Lime LM (5.66x103±i .15) and Control (8.33x103±i .15), significant variation in fungal population was found between control and treated plots (organic and inorganic) at the first month(June) and gradually reduced in second(July) and third month(August), in other treatments except with lime treatment respectively. While nitrogen fixing bacteria showed that NPK soil sample recorded the highest population of 10.3 3x103±1 . 17CFU/g) PM (7.00x103±1. 14 CFU/g) NPK+PM+LM (8.33x103±1.15CFU/g) LM (3.66x103±1.12 CFU/g). The trend was same in the second and third months respectively. Inorganic fertilizers resulted in low organic carbon content, microbial counts and microbial biomass carbon of the soil, although it increased the soil's NPK level which could be explained by the rates of fertilizers being applied. Microbial isolates and percentage occurrence showed Staphylococcus aureus(100%), Bacillus cereus (100%), Escherichia coli (60.0%), Pseudomonas aeruginosa (80.0%), Streptococcus pyo genes (40.0%), Proteus mirabilis(73.3%), Kiebsiella pneumoniae (53.3%), Azotobacter (60.0%), Enterobacter cloacae (53.3%), Salmonella sp (53.3%), Penicillium (60.0%), Acinetobacter calcoaceticus (60.0%), Micrococcus(53.3%), Rhizobium (60.0%), clostridium sp (100%), Aureobasidium sp (40.0%), Aspergillus flavus (53.3%), Monilia (40.0%), Fusarium semitectu (53.3%), Clasdosporium (40.0%), Penicilliuin nalgiovense (53.3%) and Aspergillus niger (86.7%). All the isolates showed 99% molecular similarity in reference to molecular gene bank when compared with biochemical characterization and identification. A link between different fertilizers application and soil microbial components was tentatively established, but needs to be verified in further studies.