3.2 Changes in soil properties
Changes in soil physicochemical and biological properties after 1 and
5-years of grass-legume revegetation were significantly different from
natural forest soils (Table 3). The disturbed topsoil prior to
grass-legume seeding had a pH (4.7), BD (1.26 g cm-3),
Av-N (46.68 mg kg-1), TN (389.60 mg
kg-1), SOM (0.81%), SOC (0.34%), Av-P (0.74 mg
kg-1), UA (1.26 µg
NH4+ g-1h-1), DHA (1.57 µg TPF g-1h-1) and CEC (5.23 cmol (p+)
kg-1). Changes in soil pH (5.8-5.6) with increasing
age of revegetation were not significant (p>0.05). BD
showed an increasing trend with soil depth and found highest in 1-year
revegetated soil. A significant increase in the mulch density over the
years resulted in favorable soil conditions which help increase the
topsoil moisture content of the reclaimed waste dump from 3.8 to 11.8%
compared to a natural forest (7.20%) and decrease soil temperature
(26-230C) at the top layer (0-10 cm) (Table 3; Figure
4). SOC concentrations doubled in 5-years and significantly different
(p<0.05) in both the soil depth. SOM concentration improved
due to enrichment of grass-legume mulch which decomposed over the years
but significantly lower compared to forest soil. Soil Av-N and Total-N
concentrations were significantly greater after 5-years (132 and 1165 mg
kg-1) compared to initial concentrations (54 and 579
mg kg-1) in the top layer. Decrease soil C:N ratio
justifies greater accumulation of N over C due to an abundance of legume
biomass residue. Both DHA and UA reduced with soil depth as maximum
interaction of soil microbes was found to occur in the top surface (0-10
cm). Highest DHA was observed in forest soil (10.14 µg TPF
g-1 h-1) whereas DHA in reclaimed
soil increased significantly (p<0.05) from 3.7 to 5.32 µg TPF
g-1 h-1 (Table 3). Similarly, UA
also showed a significant increase from 4.57 – 7.11 µg
NH4+ g-1h-1 among the revegetated sites during 1 to 5-years
but non-significant when compared to forest soil. Soil C and N stocks
increased significantly with revegetation age and decreased with the
soil depth (Table 4). After 5-years of grass-legume revegetation SOC
stock increase by 66% in the top layer. Soil N stock was also
significantly higher (p<0.05) after 5-years of revegetation
(1.47 ± 0.21 Mg ha-1) compared to forest N stock (1.00
± 0.32 Mg ha-1).
Additionally, an increase in mulch thickness (0, 3, 6, 9, and 12 cm) on
the dump surface accelerated the soil microbial biomass C and N even in
the early stages of revegetation promoting soil fertility. The level of
improvement was highest with 12 cm mulch thickness for all the assessed
soil parameters (Figure 7). The amount of potentially mineralizable
biomass residues in the soil correlated positively with N pool, SOM,
microbial, and enzyme activity (Table 5). Soil CO2 flux
rates differ significantly under different land covers and showed peak
values for NF (Figure 8). The mean soil CO2 flux was
found in the order of natural forest (3.17 ± 0.55µmol
m-2 s-1) > 5-years
(1.21 ± 0.15µmol m-2 s-1)
>1-year (1.01 ± 0.62µmol m-2s-1) reclaimed waste dump over the experimental
periods of revegetation.