4.2. Microbial and enzymatic activity
Microbial counts (TCB, TCA and AZO), MBC, MBC and BSR were highest in WZ soil could be related to producing greater root biomass and its exudates thereby producing higher cane yield as 25% extra N fertilizers applied over the recommended dose than CZ and EZ due to low initial N status (<280 kg N ha-1). As a result, microbial counts accelerated their growth by enhancing nutrient availability which used as carbon substrate (Meena et al., 2014; Shukla et al., 2020). The greater microbial counts, root biomass and its exudates liable to enhanced MBC and MBN as are mull to the living part of organic matter, and augmenting BSR by accelerating microbial residues decomposition process (Vinhal-Freitas et al., 2017). Though, the excess N fertilization had negative correlation with microbial activity, but lower Na (<280 kg N ha-1) across the cane producing zones of Uttar Pradesh (98.2% soil samples) had positive effects on microbial growth. The neutral soil pH and greater availability of macro and micro-nutrients favorable for fungal counts resulted more in CZ soils. Our results supported by Graham & Haynes (2005) and Vieira-Megda et al. (2015) who suggested that moderate and high N fertilization induced microbial population in sugarcane thereby increased MBC and MBN. The lowest MBC, MBN and BSR in EZ soils coupled with N, P, K and S deficiency affected synthesis of microbial biomass. In addition, higher micronutrient caused adverse effect on microbial accounts as our results also showed significant negative correlations to these nutrients with TCB, TCA and AZO (Table S3).
Soil enzymes are integral parts of soil fertility as it played crucial role in nutrient recycling, decomposition and nutrient fixation. The FDA, β-glucosidase and urease activities were more in CZ soils could be due to lower pH value, and greater macronutrient and microbial counts led to enhance their activity as these factor played vital role in microbial and enzyme activation. Also, N is a crucial edaphic factor essentially required in large quantity for achieving higher cane productivity, and microbial growth, since it used as substrate and energy source during trash decomposition due to high C: N ratio (108:1). Hence, FDA, β -glucosidase and urease had significant positive correlation with soil pH and Na (Table 3S). Reversely, lowest enzyme activities in EZ soils associated to higher soil pH, moisture content and lower microbial activities thereby inhibited synthesis and secretion of these enzymes (Zhang et al., 2014). The change in osmotic potential and specific ion toxicities (Rietz & Haynes, 2003) linked to lower urease activity in EZ soils. However, higher moisture content augmented DHA as active dehydrogenases utilized both O2 and other compounds as terminal electron acceptors, although, anaerobic microorganisms liable to produce most of the dehydrogenases (Brzezińska et al., 2001). In addition, DHA showed metabolic ability of soil proportional to SOC, as a result significant positive relation was existed between SOC and DHA. Association between DHA and total microbial activity is not always evident notably in complex soil system, wherein microbial counts actively involved in the degradation of various organic compounds that are highly diverse (Salazar et al., 2011). Hence, a significant negative correlation of DHA with microbial counts was found in our study (Table S3). ACP and ALP was highest in WZ soil could be connected to higher counts of bacteria, and MBC and FDA (Table 3) thereby induces the synthesis and secretion of phosphomonoesterases enzymes. Our results clearly indicated that ACP had significant positive correlation with TCB, MBC and FDA (Table 3S).