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).