Long-Term Effect of Organic Manuring and Inorganic Fertilization on Humus Fractionation, Microbial Community and Enzymes Assay in Vertisol

Investigations were carried out during 2011-12 and 2012-13 to evaluate the long term effect of organic manuring and inorganic fertilization on humus fractions, microbial and enzymatic activities in a Vertisol (Typic Haplusterts) by collecting soil samples from long-term fertilizer experiments commenced from 2006-07 at V. N. Marathwada Agricultural University, Parbhani, Maharashtra, India under an intensive soybean-safflower cropping system. Two years pooled results indicated that continuous cultivation with addition of 100% NPK along with organic farm yard manure (FYM) significantly improved the content of soil humin, humic acid, fulvic acid and humic acid: fulvic acid (HA:FA) ratio. The treatment also contributed significantly to the biological properties of soil with respect to CO2 evolution (56.40 mg 100 g-1 soil 24 hr-1), soil microbial biomass carbon (300.10 µg g-1), soil microbial biomass nitrogen (52.32 µg g-1), soil bacteria (229.42 CFU x 107 g-1soil), soil actinomycetes (54.53 CFU x 106 g-1soil), dehydrogenase enzyme (51.07 µg TPF g-1soil 24 hr-1), acid and alkaline phosphatase (76.08 and 160.65 µg p-NP g-1 soil 24 hr-1) activity under the soybean-safflower cropping system. However, soil fungi (8.68 CFU x 104 g-1 soil) increased significantly due to the application of only 10 Mg ha-1 FYM and it was at par with 100% NPK+FYM. Further, treating plots with 150% NPK was found equally good in improving soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN) and soil organic carbon (SOC). It can be concluded from these experimental findings that the balanced use of fertilizers continuously either alone or in combination with organic manure is necessary for sustaining soil health in a soybean-safflower cropping system on Vertisols.