4.1. Physical and chemical properties of soils
Sugarcane mono-sequencing over the years degraded agro-ecosystem due to
alteration of physical, chemical and biological properties of soil, and
destroy self-adjustment capability of the ecosystem (Lin et al., 2012).
Magarey (1996); Pankhurst et al., (2003) and Lin et al. (2012) revealed
that several factors like as imbalance fertilization and excessive use
of agrochemicals, tillage, mechanical harvesting and haul-out with heavy
machinery are accountable for the degrading physical, chemical and
biological attributes of soil under long-term sugarcane monoculture. The
MC, soil pH, SOC, and micro-nutrients (Zn, Cu, Fe and Mn) were higher in
EZ soils than CZ and WZ due to low-lying areas which hold more moisture
content. Quietly higher soil pH in EZ could be related to accumulate
more basic cations in upper surface of soil (Jenny, 1941). The SOC was
increased by 14.1 and 11.8% in EZ soils than CZ and WZ, respectively
due to more organic matter added through newly developed roots in low
lying areas. Hidaka et al. (2007) also suggested that newly developed
cane roots shared more in dry matter accumulation under flooding
condition. Reversely, decreased SOC in WZ and CZ soils than EZ was
associated with excess management practices followed in soil preparation
(chiseling, plowing and harrowing) resulting exposed soil
micro-aggregates favours C mineralization, and increasing
CO2 emissions (Moscatelli et al., 2007). Naranjo et al.
(2006) supported our results as 17% decline in total soil carbon over
the 30 years of sugarcane monoculture compared to natural land uses
(Naranjo et al., 2006).
The low Na, Pa, Ka and
Sa were in EZ soil might be due to lower doses of
mineral fertilizers were applied even though recommended dose of mineral
fertilizers (150, 60 and 60 kg N, P2O5and K2O ha-1). It mismatches between
nutrient applied and removal (205, 53 and 280 kg N, P and K for the
production of 100 Mg cane yield ha-1) over the decades
caused nutrient imbalances (Shukla et al., 2017). Moreover, low lying
area led to decrease Na through leaching and
denitrification. Similarly, Pa also decreased in EZ soil
through surface overflow and greater soil pH. Hart, Quin, & Nguyen,
(2004) reported P loss via runoff, which ranged between 0.7 and 42% of
the fertilizer applied. Hence, low Pa in EZ soil related
to higher soil pH and moisture content as significant negative
correlation existed among them (Table 3S). The lowest Sain EZ due to gradual removal from the soil as leaching, overflow and
through plant removal, but it could not applied as mineral fertilizers
regularly (Shukla & Lal, 2004). The low-lying areas that waterlogged
during monsoon season caused favorable condition to reduce
Cu+, Fe2+ and Mn+resulting to increase its availability in EZ sols. Contrary to that,
decrease Zn, Cu, Fe and Mn availability in WZ soil due to greater redox
potential liable to converted Cu+ to
Cu+2, Fe+2 to Fe+3and Mn+2 to Mn+4 (Pavanasasivam &
Axley, 1980). Further, harvesting more cane yield in WZ zone thereby
reduced its availability due to its greater mining through crop removal.