2.1. Study site, soil sampling and nutrient analysis
The current study was undertaken in key cane producing districts of Kushinagar (Eastern zone-EZ), Sitapur and Lakhimpur-kheri (Central zone-CZ), and Muzaffarnagar (Western zone-WZ) of Uttar Pradesh Province, India. The study site comprises in alluvial soil (Inceptisol) covered about 10.7×104 km2 (Fig. 1) which spreads across the subtropical zone with dry winter and hot summer. The average annual temperature and precipitation ranged from 24.2 to 31.0oC and 736 to 1000 mm, respectively (Table 1). About 131, 198 and 122 soil samples were taken through AMS auger (0-20 cm depth) on standing sugarcane crops from eastern zone (EZ), central zone (CZ) and western zone (WZ) during November-December, 2017, respectively (Table 1). Random sampling was followed, in which five samples were collected from one location, and pooled for making composite sample. Immediately after collection, moist samples were divided in two parts. In which, one parts packed separately in sterilized polythene bags and stored in ice-packed box, and finally stored in -20oC at laboratory for microbial study. Simultaneously, 100 g fresh moist samples were taken separately in moisture box for the determination of moisture content. The remaining portion of soil sample was packed in separate polythene bags, brought to the laboratory, and processed for analyzing physical and chemical attributes. Soil pH, EC, Na, Pa, Ka and Sa were analyzed as per protocol proposed by Jackson (1973). The SOC was determined by TOC analyzers (Multi N/C-2100S-Analytic-Jena), while as Zn, Cu, Fe and Mn were through atomic absorption spectrophotometer (Z2300, Hitachi Science and Technology) as per the protocol of USDA (1996).
The total culturable count of bacteria (TCB), fungi (TCF), actinomycetes (TCA) and Azotobacter ( AZO) were estimated by using nutrient agar media having 50 mg L-1 cyclohexamide (Parkinson et al., 1971), Rose Bengal chloramphenicol agar media containing 100 mg L-1 chloramphenicol (Martin, 1950), Ken Knight and Ashbys mannitol (Subba Rao, 1977), respectively through serial dilution and plate counting techniques. The chloroform fumigation-extraction method (Vance et al., 1987) was applied for determination of microbial biomass carbon (MBC), whereas, microbial biomass nitrogen (MBN) was analyzed by chloroform-fumigation-incubation and distillation method (Jenkinson & Powlson, 1976). The basal soil respiration (BSR) was analyzed through barium chloride method as suggested by Anderson (1983). The dehydrogenase activity (DHA), fluorescein diacetate hydrolytic (FDA), urease and β-glucosidase (β-glu), acid (ACP) and alkaline phosphatase activities (ALP) were determined as per the methods of Alef & Nannipieri (1995).