39

Forest soils play a vital role in the global 
carbon cycle (Detwiler and Hall, 1988; 
Jabaggy and Jackson, 2000). Most of the 

soil organic carbon (SOC) is stored in the upper 
layers (UNEP, 2012; Spain et al., 1983; Burke et 
al., 1989), and are at a high risk of emission to 
the atmosphere due to disturbances and land use 
changes (Lal, 2010). 

Soil fertility, an important factor which determines 
the growth of plants depends on the concentration 
of N, P, and K organic and inorganic materials, 
micronutrients and water. Lack of nutrient inputs is 
a major factor in soil degradation. Understanding 
of soil chemical reaction and processes is essential 
for developing innovative resource management 
strategies, and understanding and regulating the 
behaviour of the terrestrial ecosystem at regional 
and global scale (Tale and Ingole, 2015).

Information on soil properties with regards to 
forest soil-depth are important for sustainable 
management of forest. Soil productivity, health, 
sustainability, sequestration and emission 
potentials can be assessed by quantifying SOC 
(Vashum et al., 2016). Vertical distribution of 
SOC in relation to vegetation and land use is less 
understood (Jabbagy and Jackson, 2000). The 
soil carbon studies conducted in Nepal mainly 
focused on its relation with land use (Awasthi et 
al., 2005; Bajracharya et al., 2004, 2015; Dahal 
and Bajracharya, 2012). The tropical forest soils 
of western Nepal are less studied. Hence, the 
present study aims to investigate the top soil 
physiochemical properties in the tropical forests 
of western Terai region of Nepal in relation to 
depth.

Physicochemical properties of tropical forest top soil in 
relation to depth in western Nepal

B. Gautam1* and M. K. Chettri1

1 Department of Botany, Amrit Campus (T.U.), Kathmandu. *Email: gautambikash2007@gmail.com

Information on soil properties with regards to forest soil-depth are important for 
sustainable management of forest. The present study investigated the physicochemical 
properties of the top soil (0−30cm depth) in the three forests, viz. i) the Terai Shorea 
Forest (Bardia National Park), ii) the Evergreen Riverine Forest (Bardia National 
Park) and iii) the Puraina CF (Kailali district) of western Nepal. In the tropical forests 
of western Nepal, the soil texture is, moreover, loamy sand to sand. The soil bulk 
density ranged from 1.33−1.63 gm cm-3, and slightly increased with the increase in 
the soil-depth. The soil pH value ranged from 5.77−7.36. The soil organic carbon, total 
nitrogen (N), available phosphorus (P), and available potassium (K) were found to be 
in the ranges of 0.54−1.64%, 0.04−0.14%, 4.84−31.72 kg ha-1, and 204.35−557.44 kg 
ha-1, respectively, and all these values decreased with the increase in the soil-depth 
in both the forests of the protected area; however, this decreasing trend of the soil 
nutrients with the increase in the soil-depth was not observed in the Puraina CF as 
the values of the soil nutrients were lower within 0−10cm in the CF. The soil nutrients 
with all the depths were found to be the highest in the Terai Shorea Forest. The lower 
values of the soil nutrients in the Puraina CF were the result of resource extraction.

Keywords: Forest soil, management practice soil properties, soil nutrients, top soil

Banko Janakari, Vol 30 No. 1, 2020 Pp 39‒48https://doi.org/10.3126/banko.v30i1.29181



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Gautam & Chettri

Materials and methods

Study area

The present study was conducted in the three 
forests, viz. i) the Terai Shorea Forest situated in 
the south-western sector of the Bardia National 
Park (BNP) in western Nepal, ii) the Evergreen 
Riverine Forest situated in the south-western 
sector of the BNP, and iii) the Puraina Community 
Forest (CF) situated in Kailali district in western 
Nepal. The Bardia National Park is located 
between 28o17'−28040' N latitudes, and between 
81o12' E − 81o43' E longitudes. Similarly, Puraina 
Community Forest (CF) is located between 28o39' 
N − 28o40' N latitudes and 81o 00' E−81o01' E 
longitudes.

The Annual precipitation in the Tikapur Station, 
situated at 140 m above the mean sea level 
in Kailali district, was 1,669 mm (average of 
1987−2017, DoHM, 2019). Most of the total 
precipitation were found to have occurred 
during June−September while the least during 
November−December (Figure 1). The average 
maximum and minimum temperatures recorded 
during the period of 1987–2017 were 30.8o C and 
17.6o C, respectively (DoHM, 2019). The study 
was conducted in 2018 A. D.

0
5
10
15
20
25
30
35
40

0

100

200

300

400

500

600

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

RainFall (mm) Max. Temp. (0C) Min. Temp. (0C)

Figure 1: The average monthly temperature 
and rainfall data of Tikapur Station, Kailali 
district during 1987–2017 (Source: DoHM, 
2019)

The Terai Shorea Forest is mainly dominated 
by Shorea robusta followed by Terminalia alata 
(Shrestha and Jha, 1997; Giri et al., 1999). The 
Evergreen Riverine Forest is dominated mainly by 
four tree species, viz. Syzygium cumini, Mallotus 
philippensis, Ficus glomerata and Schleichera 
oleosa (Shrestha and Jha 1997; Giri et al., 2001). 

There is no resource extraction from the Terai 
Shorea and Riverine forests in the protected 
areas. According to Gautam (2019), the Puraina 
CF is mainly dominated by T. alata followed by 
Anogeissus latifolius, S. robusta and S. cumini. 
According to the Puraina CF User Group, this CF 
occupied an area of 189.21 ha, and the CF User 
Group included 540 families in 2073 B.S. (Figure 
2 and 3). The settlements around the area were 
growing rapidly, increasing pressure in the forest. 
Although, cattle grazing and resource extraction 
were banned by the authorities, illegal logging 
and resource extraction were still the main 
challenges. According to the locals, forest fire 
prevention/control and plantations in the barren 
areas were the positive approaches initiated by 
the CF User Group.

Figure 2: Satellite imagery of the Puraina CF 
(retrieved from the Google Earth in Dec, 2018) 
showing the locations of the sample plots



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Gautam & Chettri

Figure 3: Satellite imagery of the Bardia National 
Park (retrieved from the Google Earth in Dec, 
2018) showing the locations of the sample plots

Soil sampling 

The soil sampling was conducted in October, 
2018. Altogether, 13 plots, each of 500 m2, were 
taken into consideration; out of the total 13 plots, 
5 plots were laid out in the Terai Shoera Forest, 4 
plots in the Evergreen Riverine Forest, and 4 plots 
in the Puraina CF. Within each plot, five quadrats, 
each of 1m x 1m size were laid using stratified 
random design. The sample plots were randomly 
marked on the basis of frequent observations. 
From each quadrat, soil samples from the depths of 
0−10cm, 10−20cm and 20−30cm were collected; 
three composite soil samples, one for each depth 
category, were prepared for each plot. Hence, a 
total of 39 composite soil samples (13 for each 
depth category) were prepared and collected. 

Soil analysis

The laboratory analysis of the soil samples 
were carried at Amrit Campus (Kathmandu) 
and Agricultural Technology Centre (Lalitpur).
The soil samples were analysed for bulk density 
using the methodology of Blake and Hartge 
(1986). Similarly, the SOC was determined 
using the Walkley and Black Rapid Titration 
Method (Walkley and Black, 1934) while the 
total Nitrogen, the available Phosphorus and the 
Available Potassium were determined by adopting 
the Kjeldahl Method, the Olsen’s Bicarbonate 
Method, and the Flame Photometer Method, 
respectively. The soil texture was determined 
using the Sieve Method, and the soil pH was 
determined electronically, on a direct-reading 
pH meter, using a saturated potassium chloride 
calomel reference electrode. 

The One-way ANOVA followed by Tukey’s 
HSD (honestly significant difference) Test was 
conducted for the soil parameters using the R 
Software (version 3.5.1). 

Results and discussion

Physical properties

Soil texture

The soil texture was found to be, moreover, 
loamy sand to sand in all the studied forests. 
The mean sand contents at all depths (0−10cm, 
10−20cm and 20−30cm) were found to be within 
the range of 82.79−92.31%, 72.88−90.76%, and 
77.30−85.69% in the Terai Shorea Forest, the 
Riverine Forest and the Puraina CF, respectively. 
Similarly, the mean silt and clay contents at 
all depths were found to be within the range 
of 5.55−6.41% silt and 1.35−4.8% clay in the 
Terai Shorea Forest, 6.65−12.56% silt and 
1.92−14.56% clay in the Riverine Forest, and 
5.39−8.82% silt and 7.35−13.87% clay in the 
Puraina CF. The vertical differences in the 
percentages of sand, silt, and clay were found to 
be statistically insignificant for all the three study 
area. The comparison of the soils at all depths 
of all the three studied forests showed that the 
difference in the percentages of sand, silt and clay 
were all statistically insignificant, except clay% 



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Gautam & Chettri

at 10−20cm depth differed significantly (p < 
0.05) among the three study area. The percentage 
of clay at 10−20cm depth in the Puraina CF was 
found to be significantly higher (13.87%, p < 
0.05) than that in the Terai Shorea Forest (1.35%, 
p < 0.05) at the same depth. 

Soil bulk density

The mean soil bulk density slightly increased with 
the increase in depth in all the three studied forest 
which is because the soil gets more compact with 
the increase in its depth. The soil bulk densities at 
all depths in the three study sites area were in the 
range of 1.33−1.58 gm cm-3, 1.35–1.58 gm cm-3, 
and 1.45–1.63 gm cm-3, respectively (Table 1). The 
bulk densities at all depths in the Puraina CF were 
found to be slightly higher than that Terai Shorea 
Forest except at 10−20cm depth where the bulk 
density of both the forests recorded equal value 
i.e.1.58 gm cm-3. Riverine forest recorded the least 
value for bulk density at all depths. It was found 
that the bulk density value of Terai Shorea Forest 
and Puraina CF (1.58 gm cm-3in both forests) at 
10-20 cm was found to be significantly higher (p 
< 0.05) than in the Riverine forest (1.35 gm cm-3) 
at the same depth. The vertical difference in the 
bulk densities of all the three forests was found 
statistically insignificant.

Chemical properties

Soil pH

The mean soil pH at all depths was found to be in 
the range of 5.77–5.80, 7.11–7.36, and 6.36–6.50 
in the Terai Shorea Forest, the Evergreen Riverine 
Forest, and the Puraina CF, respectively. The One-
way ANOVA showed that the vertical differences 
among the soil pH were statistically insignificant 
in all the three different forest study sites; however, 
the differences among the soil pH values at all 
depths in the three different forest study areas were 
statistically significant (p < 0.05, Table 1).

The soils were more acidic in the Terai Shorea 
Forest than in the Puraina CF; however, the soils 

in the Riverine Forests were slightly alkaline 
because the occasionally flooded forest soils have 
higher pH (Budke et al., 2008). This indicates 
that the forest soils in flat plains are more acidic 
as compared to the Riverine Forest soils in flood 
plains. The acidic forest soils with the pH values 
of 4.33 and 5.26 at 0−15cm depth in a community 
forest and a national forest, respectively, within 
Udayapur district have also been reported by 
Paudel and Sah (2003);with the pH values of 5.6, 
5.8 and 6.6 at 0−15cm, 15−30cm, and 30−45cm 
depths, respectively, in the forest of Sunsari 
district by Gautam and Mandal (2013); and with 
the pH value of 5.36 in the forest of Chitwan 
district by Chauhan et al. (2014). 

Soil Organic Carbon (SOC)

The percentage of the mean SOC at all depths were 
found to be the highest (1.64%, 0.96%, and 0.65% 
at 0−10cm, 10−20cm, and 20−30cm depths, 
respectively) in the Terai Shorea Forest followed 
by the Riverine Forest (0.79%, 0.63%, and 0.54% 
at 0−10cm, 10−20cm, and 20−30cm depths, 
respectively) and the Puraina CF (0.54%, 0.63%, 
0.59% at 0−10cm, 10−20cm, and 20−30cm depths, 
respectively). Generally, the mean SOC content in 
the protected areas were found to have decreased 
with the increase in depth; however, this general 
trend was not found in the Puraina CF where the 
mean SOC content (0.54%) in the uppermost 
layer (0−10cm depth) was lower than those 
(0.63% and 0.59%) in the deeper layers (10−20cm 
and 20−30cm depths, respectively) (Figure 4). 
The vertical difference in the mean SOCs was 
statistically significant (p < 0.05) in the Terai 
Shorea Forest, but insignificant in the Riverine 
Forest and the Puraina CF. The difference in the 
mean SOC sat 0−10cm depth in the three studied 
forests was found to be statistically significant (p < 
0.05), but statistically insignificant at 10−20cm and 
20−30cm depths. The mean SOC content (1.64%) 
at 0−10cm depth in the Terai Shorea Forest was 
significantly higher as compared to those in the 
Riverine Forest and the Puraina CF (0.79% and 
0.54%, respectively, Table 1).



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Table 1: Mean ± SD values of soil parameters at 0-10cm, 10-20cm, and 20-30cm depths in Terai 
Shorea Forest (TSF), Riverine Forest (RF), and Puraina CF

Soil Parameters Depth Forest Study Area
TSF RF CF

OC (%) 0−10cm 1.64 ± 0.65 a
A 0.79 ± 0.46 a 

A,B 0.54 ± 0.13 a
B

10−20cm 0.96 ± 0.41 a,b
A 0.63 ± 0.27 a

A 0.63 ± 0.1 a
A

20−30cm 0.65 ± 0.15 b
A 0.54 ± 0.27 a

A 0.59 ± 0.07 a
A

TN (%) 0−10cm 0.14 ± 0.05 a
A 0.09 ± 0.01 a

A,B 0.05 ± 0.01 a
B

10−20cm 0.08 ± 0.03 b
A 0.06 ± 0.02 a,b

A 0.05 ± 0.01 a 
A

20−30cm 0.06 ± 0.01 b
A 0.05 ± 0.02 b

A 0.04 ± 0.01 a
A

AP (Kg ha-1) 0−10cm 31.72± 10.66 a
A 12.36 ± 4.45 a

B 12.88 ± 4.25 a
B

10−20cm 16.07 ± 6.74 b
A 10.82 ± 3.90 a

A 16.41 ± 7.68 a
A

20−30cm 14.09 ± 8.87 b
A 4.84 ± 5.18 a

A 10.09 ± 1.68 a
A

AK (Kg ha-1) 0−10cm 557.44 ± 47 a
A 314.9 ± 35.45 a

B 221.1 ± 45.77 a
C

10−20cm 525.28 ± 69.24 a
A 257.95 ± 50.58 a

B 204.35 ± 35.24 a
B

20−30cm 470.2 ± 120.62 a
A 241.2 ± 66.55 a

B 224.45 ± 58.28 a
B

pH 0−10cm 5.78 ± 0.05 a
A 7.11 ± 0.41 a

B 6.50 ± 0.51 a
B

10−20cm 5.77 ± 0.11 a
A 7.25 ± 0.18 a

B 6.45 ± 0.47 a
C

20−30cm 5.80 ± 0.20 a
A 7.36 ± 0.05 a 

B 6.36 ± 0.54 a
A

BD (gm cm-3) 0−10cm 1.46 ± 0.11 a
A 1.33 ± 0.15 a

A 1.58 ± 0.13 a
A

10−20cm 1.58 ± 0.08 a
A 1.35 ± 0.10a

B 1.58 ± 0.05 a
A

20−30cm 1.58 ± 0.11 a
A 1.45 ± 0.10a

A 1.63 ± 0.05 a
A

Sand (%) 0−10cm 82.79 ± 11.97 a
A 72.88 ± 28.42 a

A 84.76 ± 4.4 a
A

10−20cm 92.31 ± 5.7 a
A 88.16 ± 13.12 a

A 77.30 ± 13.53 a
A

20−30cm 90.77 ± 5.57 a
A 90.76 ± 6.81 a

A 85.69 ± 10.89 a
A

Silt (%) 0−10cm 6.41 ± 5.4 a 
A 12.56 ± 13.47 a 

A 5.39 ± 1.21 a 
A

10−20cm 6.27 ± 4.81 a 
A 6.82 ± 8.61 a 

A 8.82 ± 4.88 a 
A

20−30cm 5.55 ± 2.90 a 
A 6.65 ± 5.75 a 

A 6.96 ± 3.96 a 
A

Clay (%) 0−10cm 4.8 ± 2.59 a 
A 14.56 ± 15.06 a 

A 9.85 ± 3.49 a 
A

10−20cm 1.35 ± 0.84 a 
A 5.01 ± 4.6 a 

A,B 13.87 ± 9.38 a 
B

 20−30cm 3.75 ± 3.33 a 
A 1.92 ± 1.62 a 

A 1.35 6.94 a 
A

Note: Different letters in superscript (small alphabets) implies significant difference for each soil 
parameters along a depth gradient for each forest. Different letters in subscript (capital alphabets) implies 
significant difference in soil parameters between the three forests at a particular depth



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Gautam & Chettri

Figure 4: Diagrammatic representation of the vertical distribution of mean SOC, total nitrogen, 
available phosphorus and available potassium in three different forest study areas

Total Nitrogen

The total nitrogen content in the Terai Shorea 
Forest (0.14%, 0.08% and 0.06% at 0−10cm, 
10−0cm, and 20−30cm depths, respectively) were 
found to be higher than that in the Riverine Forest 
(0.09%, 0.06%, and 0.05% at 0−10cm, 10−20cm, 
and 20−30cm depths, respectively) and the 
Puraina CF (0.05%, 0.05%, and 0.04% at 0−10cm, 
10−20cm, and 20−30cm depths, respectively). 
The vertical differences in the mean soil nitrogen 
content were statistically significant (p < 0.05) in 
the Terai Shorea and Riverine forests; however, 
the differences were statistically insignificant in 
the Puraina CF. The mean soil nitrogen content 
in the three forest study sites was found to have 
differed significantly at 0−10cm depth, but not 
so at 10−20cm and 20−30cm depths. The mean 
soil nitrogen content at 0−10cm depth in the Terai 
Shorea Forest was significantly higher than that 
in the Puraina CF (Table 1).

Available Phosphorus

The mean available phosphorus was found to 
have decreased with the increase in depth in the 
Terai Shorea Forest (31.72 kg ha-1, 16.07 kg ha-

1, and 14.09 kg ha-1 at 0−10cm, 10−20cm, and 
20−30cm depths, respectively) and the Riverine 
Forest (12.36 kg ha-1, 10.82 kg ha-1, and 4.84 

kg ha-1 at 0−10cm, 10−20cm, and 20−30cm 
depths, respectively). In the Puraina CF, the mean 
phosphorus content was highest (16.41 kg ha-1) 
at 10−20cm followed by 0−10cm (12.88 kg ha-1) 
and 20−30cm (10.09 kg ha-1). The vertical 
difference in the mean available phosphorus was 
statistically significant (p < 0.05) only in the Terai 
Shorea Forest, and insignificant in the Riverine 
Forest and the Puraina CF. The mean soil 
phosphorus contents in the three forest study area 
were statistically significant (p < 0.05) at 0−10cm 
depth; however, insignificant at 10−20cm and 
20−30cm depths. The mean value of the available 
phosphorus at 0−10cm depth in the Terai Shorea 
Forest was significantly higher than that in the 
Riverine Forest and Puraina CF (Table 1).

Available Potassium

The mean available potassium decreased with 
the increase in depth in the Terai Shorea Forest 
(557.44 kg ha-1, 525.28 kg ha-1, and 470.2 kg 
ha-1 at 0−10cm, 10−20cm, and 20−30cm depths, 
respectively) and the Riverine Forest (314.9 kg 
ha-1, 257.95 kg ha-1, and 241.2 kg ha-1 at 0−10cm, 
10−20cm, and 20−30cm depths, respectively). In 
the Puraina CF, the decreasing trend of potassium 
content with the increase in depth (221.1 kg ha-

1, 204.35 kg ha-1, and 224.45 kg ha-1 at 0−10cm, 
10−20cm, and 20−30cm depths, respectively) 



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Gautam & Chettri

was not observed. The mean potassium contents at 
all depths were highest in the Terai Shorea Forest 
followed by the Riverine forest and the least in 
the Puraina CF. The vertical differences in the 
mean potassium content in the three forest study 
area were found to be statistically insignificant; 
however, the mean available potassium content in 
the three studied forests at all depths were found 
to be statistically significant (Table 1).

In the present study, the mean SOC percent, 
total nitrogen percent, available phosphorus and 
available potassium (kg ha-1) decreased with 
the increase in soil depth in the protected area. 
Similar decreasing trend of SOC with increase in 
depth has been reported in a number of literatures 
(Vsahum et al., 2016; Jabbagy and Jackson, 2000; 
Dorji et al., 2014). Yang et al. (2010) reported 
that both SOC and total nitrogen decreased with 
increase in depth, however the C:N ratio did not 
change. Gautam and Mandal (2013) also observed 
the decreasing SOC and total nitrogen with the 
increase in depth in the tropical moist forest of 
Sunsari, Nepal. 

In the Puraina CF, the mean values of the 
soil nutrients (SOC, total nitrogen, available 
phosphorus, and available potassium) in the 
upper most layers were low, and hence the trend 
of decreased soil nutrients with the increase in 
soil depth was violated. The lower values of the 
soil nutrients in the Puraina CF could be probably 
due to anthropogenic disturbances. The wood 
and fodder needs of the CF users were mostly 
met from the extraction of the same from their 
CF. Forest harvesting caused a sharp decline in 
the SOC stock as much as 50% within the first 
20 years or more (Johnson, 1992; Davidson and 
Ackerman, 1993; Lal, 2005). The decline in SOC 
in harvested forests is probably due to decreased 
litter input, shifts in composition of woody and 
herbaceous vegetation, distribution of plant roots, 
accelerated decomposition and decreased net 
primary production (Covington, 1981; Johnson et 
al., 1995; Jackson et al., 2000).

The presence of soil nutrients at all depths in 
the Terai Shorea Forest was found to be higher 
than those in the Riverine Forest and the Puraina 
CF (Table 1). This could be attributed to the 
natural strains, tree species composition, and 
management practices adopted in those forests. 
According to the locals, the Terai Shorea Forest 
used to encounter summer fire episode while the 

Riverine Forest monsoon flooding. On the other 
hand, the Puraina CF encountered anthropogenic 
disturbances such as lopping, logging, and 
resource extraction. The SOC in the present study 
sites were lower than those (3.07%, 1.34%, and 
1.17% at 0−15 cm, 15−30 cm, and 30−45 cm 
depths, respectively, in a Sal bearing moist forest in 
Sunsari district) reported by Gautam and Mandal 
(2013), and those (1.86% and 2.03% at 0−15 cm 
depth, respectively, in a community-managed 
forest and a protected forest within the Panchase 
area) reported by Kalu et al. (2014). This could be 
possibly attributed to the lesser amount of the total 
precipitation in the present study sites as compared 
to its occurrence in the Panchase area since SOC 
increases with increased precipitation (Jabbagy 
and Jackson, 2000). Duration of monsoon and 
total precipitation gradually decreases from east 
to west in Nepal (Bohlinger and Sotreberg, 2017). 
Despite the difference in total precipitation, the 
SOC content in the protected Terai Shorea Forest 
of the present study was similar to those (1.4% and 
1% at 0−15cm depth in a community-managed 
forest and a national forest with free access 
to the local people, respectively in Udayapur 
district) reported by Paudel and Sah (2003); those 
(0.65−2.39% at 0−30cm depth in a community-
managed forest in Syangja district) reported by 
KC et al. (2013); and those (1.98% at 0−20 cm 
depth in a community-managed forest in Chitwan 
district) reported by Chauhan et al. (2014). The 
presence of low amount of SOC in the Puraina 
CF could be probably due to resource extraction 
from this CF. 

The total nitrogen content at all depths in the 
present study sites were lower than those (0.24%, 
0.24%, and 0.09% at 0−15cm, 15−30cm, and 
30−45cm depths, respectively, in the Sal bearing 
moist forest in Sunsari district) reported by Gautam 
and Mandal (2013), and those (0.21% and 0.29% 
at 0−15cm depth in the community-managed 
forest and the protected forest, respectively, in 
the Panchase area) reported by Kalu et al. (2014). 
The total nitrogen content (at 0−15cm depth)in 
the Terai Shorea Forest was also similar to those 
(0.117% and 0.111% at 0−15cm depth in the 
community-managed forest and the national forest 
with free access to the local people, respectively, 
in Udayapur district) reported by Paudel and Sah 
(2003); that (0.09−0.12% at 0−30cm depth in the 
community-managed forest in Syangja district) 
reported by KC et al. (2013) and the one (0.19% 



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Gautam & Chettri

at 0−20cm depth in the community-managed 
forest in Chitwan district) reported by Chauhan 
et al. (2014). This indicated a strong relationship 
between SOC and total nitrogen. 

The available phosphorus in the present study 
sites were comparatively lower than those (76.64 
kg ha-1 and 79.29 kg ha-1 at 0−15 cm depth in 
the community-managed forest and the national 
forest with free access to the local people, 
respectively, in Udayapur district) reported by 
Paudel and Sah (2003) and that (73.71–93.23 kg 
ha-1 at 0−30cm depth in the community-managed 
forest in Syangja district) reported by KC et al. 
(2013). 

The available potassium (2.54–4.23 kg ha-1 at 
0−30cm in the community-managed forest in 
Syangja district) reported by KC et al. (2013), 
and the one (79.5 kg ha-1 at 0−20cm depth in 
the Seti Devi CF of Chitwan district) reported 
by Chauhan et al. (2014) were comparatively 
lower than that recorded in the present study 
sites. However, the available potassium (267.73 
kg ha-1 and 233.86 kg ha-1 at 0−15 cm depth in 
the community-managed forest and the national 
forest, respectively, in Udayapur district) reported 
by Paudel and Sah (2003) were similar to that in 
the protected Riverine Forest and the Puraina 
CF, but lower than the one in the protected Terai 
Shorea Forest. 

Relationship among soil parameters

The soil nutrients (SOC, total nitrogen, available 
phosphorus and potassium) showed significant 
positive correlation (p < 0.05) among themselves 
(Table 2). The soil pH value showed significant 
negative correlation (p < 0.05) with the SOC, total 
nitrogen, available phosphorus and potassium, 
and bulk density (Table 2). The percentage of 
sand was found to be significantly negatively 
correlated with the percentages of silt and clay 
(Table 2). However, the percentages of silt and 
clay showed significant (0.72, p < 0.05) positive 
correlation. 

The SOC, total nitrogen and available phosphorus 
were found to be negatively correlated with the 
bulk density and sand content. Available potassium 
had zero correlation with the soil bulk density 
and positively correlated with the sand content. 
The SOC and the available phosphorus were 

positively correlated to the silt and clay contents. 
The total nitrogen was positively correlated with 
the silt while negatively correlated with the clay 
contents. The available potassium was found to 
be negatively correlated with the silt and clay 
contents. The pH value was negatively correlated 
with the sand and positively correlated with 
the silt and clay contents. The soil bulk density 
was positively correlated with the sand while 
negatively correlated to the silt and clay contents. 
However, these correlations were statistically 
insignificant (Table 2). 

Table 2: Pearson Correlation Coefficient 
values among the soil parameters

 OC TN AP AK  pH  BD Sand  Silt  Clay
OC 1 0.94* 0.54* 0.54* −0.32* −0.14 −0.19 0.22 0.01
TN 1 0.57* 0.58* −0.33* −0.18 −0.12 0.13 −0.06
AP 1 0.49* −0.5* −0.12 −0.1 0.04 0.09
AK 1 −0.67* 0 0.11 −0.13 −0.25
pH 1 −0.43* −0.2 0.23 0.25
BD 1 0.17 −0.14 −0.18
Sand (%) 1 −0.84* −0.88*
Silt (%) 1 0.72*
Clay (%)         1

Note:- OC : Organic Carbon, TN : Total Nitrogen, 
AP : Available Phosphorus, AK : Available 
Potassium, and BD : Bulk Density; *p< 0.05

Statistically significant strong positive correlation 
(0.94) was found between the SOC and the total 
nitrogen. Similar significant correlation between 
the SOC and the total nitrogen was also observed 
by Gautam and Mandal (2013) in the Sal-bearing 
tropical moist forest of Sunsari district. Positive 
correlation between the SOC and the total nitrogen 
was observed by Paudel and Sah (2003) in the 
forests of Udayapur district and by Chauhan et 
al. (2014) in Chitwan district. The SOC and the 
total nitrogen, both showed significant positive 
relationships with the available phosphorus and the 
available potassium. The SOC, the total nitrogen, 
the available phosphorus, the available potassium 
and the bulk density showed significant negative 
relationships with the soil pH. The SOC, the 
total nitrogen and the available phosphorus also 
showed negative relationships with the soil bulk 
density while the available potassium showed zero 
correlation with the soil bulk density, but statistically 
insignificant. Similar to our results, Paudel and Sah 
(2003) had also observed negative correlation of 
soil pH with organic matter and nitrogen, positive 
correlation of organic matter with nitrogen and 
phosphorus, and positive correlation between 
nitrogen and potassium. Chauhan et al. (2014) had 



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47

Gautam & Chettri

also reported negative correlation between total 
nitrogen and soil bulk density in Chitwan district.

Conclusion

In protected forests, SOC, total nitrogen, available 
phosphorus and available potassium generally 
decrease with increase in soil depth. However in 
the Puraina CF, this trend was not observed. The 
soil nutrients in the Puraina CF were found to be 
lower than in the protected forests which could be 
because of the extraction of resources from the CF.

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