4.2 Effect of grass-legume mixture on SOM and enzymes activity
Soil fertility in terms of SOM, C and N concentration readily declines
in topsoil during initial use at the waste dumpsite, which can be
recovered through revegetation and subsequent nutrient cycling via
decomposition and mineralization (Campos, Etchevers, Oleschko, &
Hidalgo, 2014; de Oliveira et al., 2015; Semenov et al., 2019). Analysis
of variance (ANOVA) showed that the growth of grass-legume mixture on
dump surface bought significant changes in both above and below-ground
soil systems (Table 3). Enrichment of grass-legume mulch over 5-years of
revegetation increased the SOC and SOM concentration by 94% and 35%
respectively in 0-10 cm depth. However, when compared with forest soil,
both SOC and SOM concentration was still 23% and 111% lower in
reclaimed soil. Similarly, SOC and N stock in the blanketed soil also
showed increment by 66% and 122%, respectively, after 5-years compared
to initial concentration (Table 4). These differences are mainly
attributed to the presence of rapidly decomposing legume residue,
impedes the recovery of SOM, and potentially available forms of C and N
pool governed by soil microbes and plant rooting depth will absorb a
large amount of the nutrient, leading to increased microbial activity.
Previous studies have also reported that the incorporation of legume
biomass helps in the recovery of soil C (Guan et al., 2016; Wu, Liu,
Tian, & Shi, 2017) and N stock in the early stage of biological
reclamation (Ahirwal, Maiti, & Reddy, 2017a; Elgersma & Soegaard,
2016).
The changes in root and shoot biomass and mulch accumulation in mixture
modifies the composition of mulch residue added to the soil, which
resulted from an increase in N mineralization, promotes C and N recovery
link to increase soil microbial biomass C and N (Figure 7). At the same
time, enzymes related to soil C and N decomposition processes i.e.
dehydrogenase and urease enzyme activity demonstrate 56 and 44%
increase, respectively after 5 years of revegetation compared to
1st year which probably reflected the general build-up
of the microbial biomass. These results show the positive correlation
and linkage between nutrient parameters, microbial and enzyme activities
in a high decomposition driven soil environment (Table 5) that are in
agreements with the similar trends explained in other studies (Hou et
al., 2018; Luo et al., 2018; Zuber & Villamil, 2016). During land use
change, plantation of legume (M. sativa ) significantly improved
the soil N concentration and urease enzyme activity after 3-years of the
plantation (Yu, Lin, Liu, & Wang, 2020). Our finding illustrates the
fact that reclaimed soils under grass-legume revegetation have higher N
mineralization potential and beneficial for the growth of soil microbial
biomass that is related to enzyme activities that play a crucial role in
effective recovery of soil nutrients during revegetation.