Soil texture of agroforestry systems was found to be sandy loam, sandy clay loam, sandy, silt loam, clay loam, loamy and loamy sand. Soil pH and Electrical conductivity ranged from 6.77–8.10 and 0.18–0.37 dS m− 1, respectively. The soils of agroforestry systems were neutral to slightly alkaline in reaction.
The results revealed that soil organic carbon contents were significantly affected by different land use systems. There is interaction between the land use system and soil depth. Status of soil organic carbon in land use systems at two depths was given in table.I.
Significantly higher soil organic carbon recorded in eucalyptus land use system (6.17 g kg− 1) at 0–20 cm depth which was on par with the land use system of subabul (6.10 g kg− 1), teak (6.07 g kg− 1) and red sanders (5.97 g kg− 1) at surface depth, where more residue was added through leaf litter (Mengistu et al., 2020) and different from all other land use systems. Significantly lower soil organic carbon recorded in barren land in both the depths 0–20 cm (2.33 g kg− 1) and 20–40 cm (1.41g kg− 1) due to low residue accumulation. The huge amount of residues (leaves, branches, bark and especially roots) produced by the eucalyptus spp. plantation attributes to higher contents of organic matter. This output is in conformity to Leite et al. (2010).
This enrichment in organic carbon content under tree-based systems could be due to several factors such as contribution by litter fall, root biomass, and root exudates and recycling of aboveground plant parts in a natural process (Sharma et al., 2009). High SOC levels in the rhizosphere of tree species could be attributed to more soil organic matter accumulating under the canopy (Wang et al., 2016), which decomposes quickly due to a modified microclimate (Jackson et al., 2019). The supply of C to the rhizosphere through plant roots may affect the decomposition of the SOM (Finzi et al., 2015). The presence of soluble and insoluble forms of organic C such as sugars, organic acids, mucilage, sloughed cell walls and root hairs, are also responsible for enhanced SOC in the tree rhizosphere (Hütsch et al., 2002). Variations in organic carbon content in soils under various tree species is attributed to the age of plantation and amount of litter fall, their biochemical composition and rate of their decomposition. These results are in conformity with Bhavya et al. (2018).
Significantly higher organic carbon pools were recorded in eucalyptus land use system (VLC − 3.21 g kg− 1), (LC – 1.95 g kg− 1), (LLC – 1.94 g kg− 1), (NLC – 1.91g kg− 1) and (TOC-9.02 g kg− 1) and significantly low organic carbon pools were recorded in barren land (VLC-1.37 g kg− 1), (LC-0.81 gkg− 1), (LLC − 0.81 g kg− 1), (NLC − 0.85 g kg− 1) and (TOC − 3.84 g kg− 1). Soil organic carbon pools significantly decreased from 0–20 cm to 20–40 cm soil layers in all the land use systems. This was due to continuous litter fall in tree based land use systems and also weed growth on barren land which could accumulate organic matter in the surface layers. Similar results were also confirmed by Kumar et al. (2020). There was interaction between land use systems and soil depth. Significantly highest soil organic C pools (VLC- 3.64 g kg− 1), (LC – 2.56 g kg− 1), (LLC – 2.11 g kg− 1), (NLC – 2.06 g kg− 1) and (TOC- 10.37 g kg− 1) were recorded at 0–20 cm soil depth in eucalyptus land use system and significantly lowest soil organic C pools (VLC- 1.10 g kg− 1), (LC – 0.51 g kg− 1), (LLC – 0.66 g kg− 1), (NLC – 0.88 g kg− 1) and (TOC- 3.15 g kg− 1) recorded at 20–40 cm in barren land (table 4).
Mean values with lower case superscript letters indicate significant difference between land use systems for each soil depth and all land use systems. Uppercase superscript letters indicate significant difference between depth and all land use systems, respectively at (p < 0.05).
± indicates standard deviation of mean.
Results also revealed that active pools dominated over the passive pools (Fig. 1) in all the land use systems and barren land for both soil depths. This might be because tree based land use systems had significant labile carbon pool as compared to uncultivated land (Kumar et al., 2020). In all the studied land use systems, the active pool of soil organic carbon was significantly higher in eucalyptus land use system (VLC – 3.21 g kg− 1 and LC- 1.95 g kg− 1) this might be due to the regular accumulation of leaf litter and presence of newly added organic matter. Significantly higher proportion of passive pool (LLC – 1.94 g kg− 1, NLC- 1.91 g kg− 1) was recorded in eucalyptus land use system, might be due to stabilization of added plant residues by humification process (Kaushik et al., 2018a). Land use seems to have in much bigger influence on labile C pools than the inherent soil properties (Sharma et al., 2014). Lowest active and passive carbon proportion was recorded in barren land (VLC – 1.37 g kg− 1, LC − 0.81 g kg− 1) and (LLC-0.81 g kg− 1, NLC – 0.85 g kg− 1) is attributed due to the presence of poor organic matter. All organic carbon fractions of different lability (VLC, LC, LLC, NLC) were significantly and positively correlated. All organic carbon pools were significantly and positively correlated with TOC (table.III). The results are in conformity with Sahoo et al. (2019).
Table III. Correlation between Total organic carbon and Soil organic carbon fractions
|
OC
|
Very labile
|
labile
|
Less labile
|
Non labile
|
TOC
|
WSC
|
OC
|
1
|
|
|
|
|
|
|
Very labile
|
0.918**
|
1
|
|
|
|
|
|
Labile
|
0.934**
|
0.771**
|
1
|
|
|
|
|
Less labile
|
0.907**
|
0.841**
|
0.812**
|
1
|
|
|
|
Non labile
|
0.626**
|
0.595**
|
0.579**
|
0.635**
|
1
|
|
|
TOC
|
0.970**
|
0.922**
|
0.910**
|
0.923**
|
0.768**
|
1
|
|
WSC
|
0.927**
|
0.872**
|
0.830**
|
0.931**
|
0.592**
|
0.916**
|
1
|
**. Correlation is significant at the 0.01 level (2-tailed).
Table IV. Interaction between depth and land use systems of different soil organic carbon pools
Interaction between depth (0–20 cm) and Land use systems
|
Interaction between depth (20–40 cm) and Land use systems
|
|
Verylabile (g kg-1)
|
Labile (g kg-1)
|
Less labile (g kg-1)
|
Non labile (g kg-1)
|
TOC
(g kg-1)
|
|
Verylabile (g kg-1)
|
Labile (g kg-1)
|
Less labile (g kg-1)
|
Non labile (g kg-1)
|
TOC
(g kg-1)
|
D1L1
|
3.64 ± 0.08a
|
2.56 ± 0.12a
|
2.11 ± 0.12a
|
2.06 ± 0.31a
|
10.37 ± 0.19a
|
D2L1
|
2.78 ± 0.11c
|
1.35 ± 0.10e
|
1.78 ± 0.11cd
|
1.76 ± 0.19a
|
7.66 ± 0.34de
|
D1L2
|
2.67 ± 0.10c
|
2.25 ± 0.11b
|
1.82 ± 0.10bc
|
1.00 ± 0.17c
|
7.74 ± 0.17d
|
D2L2
|
2.20 ± 0.11e
|
1.13 ± 0.08fg
|
1.46 ± 0.13f
|
0.88 ± 0.21cd
|
5.67 ± 0.22g
|
D1L3
|
3.33 ± 0.10b
|
2.34 ± 0.11b
|
1.98 ± 0.10b
|
1.10 ± 0.24c
|
8.75 ± 0.16c
|
D2L3
|
2.53 ± 0.12d
|
1.22 ± 0.10ef
|
1.67 ± 0.10h
|
1.05 ± 0.21c
|
6.47 ± 0.18f
|
D1L4
|
2.45 ± 0.08d
|
2.12 ± 0.07c
|
1.88 ± 0.12bc
|
1.27 ± 0.42c
|
7.72 ± 0.25d
|
D2L4
|
1.52 ± 0.16g
|
1.19 ± 0.15f
|
1.56 ± 0.11f
|
1.24 ± 0.18c
|
5.65 ± 0.28g
|
D1L5
|
3.35 ± 0.02b
|
2.11 ± 0.10c
|
1.85 ± 0.08bc
|
1.13 ± 0.14c
|
8.43 ± 0.20c
|
D2L5
|
2.55 ± 0.11d
|
1.31 ± 0.10ef
|
1.64 ± 0.12ef
|
0.65 ± 0.31d
|
6.14 ± 0.22f
|
D1L6
|
3.22 ± 0.10b
|
2.34 ± 0.10b
|
2.07 ± 0.15a
|
2.05 ± 0.58a
|
9.68 ± 0.24b
|
D2L6
|
2.63 ± 0.13c
|
1.18 ± 0.09f
|
1.78 ± 0.11cd
|
1.68 ± 0.42b
|
7.27 ± 0.23e
|
D1L7
|
2.22 ± 0.06e
|
2.22 ± 0.11b
|
1.83 ± 0.11bc
|
1.46 ± 0.22bc
|
7.74 ± 0.17d
|
D2L7
|
1.90 ± 0.12f
|
0.98 ± 0.12g
|
1.58 ± 0.09f
|
0.84 ± 0.18cd
|
5.30 ± 0.27gh
|
D1L8
|
2.46 ± 0.09d
|
2.17 ± 0.09bc
|
1.81 ± 0.11bc
|
1.23 ± 0.10c
|
7.68 ± 0.17d
|
D2L8
|
1.98 ± 0.12f
|
0.95 ± 0.12h
|
1.53 ± 0.13f
|
0.65 ± 0.15d
|
5.11 ± 0.27h
|
D1L9
|
2.12 ± 0.12e
|
1.86 ± 0.10d
|
1.68 ± 0.09de
|
1.25 ± 0.30c
|
6.90 ± 0.25fe
|
D2L9
|
1.85 ± 0.11f
|
0.84 ± 0.09i
|
0.97 ± 0.13g
|
0.68 ± 0.10d
|
4.34 ± 0.23i
|
D1L10
|
1.65 ± 0.09g
|
1.11 ± 0.08fg
|
0.96 ± 0.07g
|
0.82 ± 0.21cd
|
4.54 ± 0.18i
|
D2L10
|
1.10 ± 0.12h
|
0.51 ± 0.11j
|
0.66 ± 0.11h
|
0.88 ± 0.30cd
|
3.15 ± 0.33j
|
Land use systems x
Depth
|
Verylabile
|
Labile
|
Lesslabile
|
Nonlabile
|
|
|
SE(m)
|
CD
|
SE(m)
|
CD
|
SE(m)
|
CD
|
SE(m)
|
CD
|
|
|
0.06
|
0.17
|
0.06
|
0.17
|
0.06
|
0.18
|
0.16
|
0.46
|
Mean values with lower case superscript letters indicate significant difference between land use systems for each soil depth and all land use systems. Uppercase superscript letters indicate significant difference between depth and all land use systems, respectively at (p < 0.05).
±indicates standard deviation of mean.
The tree growth parameters, height, girth, biomass, carbon stock and carbon sequestration of various agroforestry tree plantations were given in tables V and VI.
The growth parameters of all the agroforestry tree plantations increased along the increase of age of plantation. The tree height and girth of eucalyptus plantation ranged from 8.5 to 18 m and 0.23 − 1.12 m (5–15 years), teak plantation ranged from 6.3 to 20 m and 0.22–0.99 m (5–20 years), malabar neem plantation ranged from 12.8 to 18.5 m and 0.56–0.85 m (5–8 years), sandalwood plantation ranged from 5.5 to 8.0 m and 0.33–0.61 m (5 to7 years), red sanders plantation ranged from 6 to 15 m and 0.25–0.95 m (5–10 years), subabul plantation ranged from 5 to 21 m and 0.25–0.95 m (5–10 years), respectively. Similar trend of increase in tree growth parameters and biomass in different tree components increased with age was noticed by Arora et al. (2017).
The above ground, below ground, total biomass, carbon stock and carbon sequestration increased along with the age gradations in all the tree plantations. The total biomass of eucayptus ranged from 8–447 kg tree− 1 (5–15 years), teak ranged from 6–384 kg tree− 1 (5–20 years), malabar neem ranged from 64–214 kg tree− 1 (5–8 years), sandalwood ranged from 18–89 kg tree− 1 (5–8 years), red sanders ranged from 9-333 kg tree− 1 (5–10 years) and subabul ranged from 6-322 kg tree− 1 (5–10 years). Biomass distribution among different components of woody perennial and variations in tree biomass may be attributed to numerous factors like plant architecture and morphology, site quality, age, density, structure, climatic, edaphic factors and management practices (Kanime et al., 2013; Goswami et al., 2014).
Carbon sequestration of eucalyptus plantations ranged from 15 to 821 kg tree− 1 (5–15 years), teak ranged from 11 to 704 kg tree− 1 (5–20 years), malabar neem ranged from 118–392 kg tree− 1 (5–8 years), sandalwood ranged from 33–164 kg tree− 1 (5–8 years), red sanders ranged from 17–611 kg tree− 1 (5–10 years), subabul ranged from 11–591 kg tree− 1 (5–10 years). The amount of carbon sequestered will largely depend on the type of agroforestry system and also on its structure and function which to a great extent, are determined by environmental and socio-economic factors. Also, tree species and system management can influence carbon storage in agroforestry systems (Albrecht and Kandji., 2003). The growth parameters in tree plantations at 10 years of age were in following order
Height
|
:
|
Subabul > eucalyptus > teak > redsanders
|
Girth
|
:
|
Redsanders > subabul > teak > eucalyptus
|
Total biomass
|
:
|
Subabul > red sanders > teak > eucalyptus
|
Carbon stock
|
:
|
Subabul > red sanders > teak > eucalyptus
|
Carbon sequestration
|
:
|
Subabul > red sanders > teak > eucalyptus
|
The growth parameters in tree plantations at 7 years of age were in following order
Height
|
:
|
Malabarneem (Malabar neem + Sandalwood - MN + SW) > eucalyptus > red sanders > sandalwood > sandalwood (MN + SW)
|
Girth
|
:
|
Malabar neem (MN + SW) > sandalwood > sandalwood (MN + SW) > eucalyptus > red sanders
|
Total biomass
|
:
|
Malabar neem (MN + SW) > sandalwood > sandalwood (MN + SW) > eucalyptus > red sanders
|
Carbon stock
|
:
|
Malabar neem (MN + SW) > sandalwood > sandalwood (MN + SW) > eucalyptus = red sanders
|
Carbon sequestration
|
:
|
Malabar neem (MN + SW) > sandalwood > sandalwood (MN + SW)
> eucalyptus > red sanders
|
The growth parameters in tree plantations at 5 years of age are in following order
Height
|
:
|
Malabar neem > eucalyptus > red sanders > teak > subabul > sandalwood
|
Girth
|
:
|
Malabar neem > sandalwood > subabul > eucalyptus > red sanders > teak
|
Total biomass
|
:
|
Malabar neem > sandalwood > subabul > eucalyptus > red sanders > teak
|
Carbon stock
|
:
|
Malabar neem > sandalwood > subabul > eucalyptus > red sanders > teak
|
Carbon sequestration
|
:
|
Malabar neem > sandalwood > subabul > eucalyptus > red sanders > teak
|
Total amount of carbon stock and carbon sequestered per tree differed significantly in all tree plantations at different ages. The carbon stock and carbon sequestration were significantly higher in malabar neem (46 kg tree− 1, 168 kg tree− 1) and lower in teak (5 kg tree− 1, 20 kg tree− 1) at 5 years of age. In tree plantations of 7 years age, the carbon stock and carbon sequestration were significantly higher in malabar neem (MN + SW) (66 kg tree− 1, 242 kg tree− 1) and lower in red sanders (17 kg tree− 1, 62 kg tree− 1).
The carbon stock and carbon sequestration were significantly higher in eucalyptus (142 kg tree− 1, 522 kg tree− 1) and lower in teak (47 kg tree− 1, 173 kg tree− 1) at 10 years of age.
Among the tree species studied, fast growing species malabar neem, subabul, eucalyptus reported higher carbon sequestration than the slow growing species teak, redsanders and sandalwood. Singh et al. (2022) also confirmed that the fast-growing tree species like casuarina, eucalyptus and malabar neem showed maximum growth performance (height, girth and biomass) thereby contributing for higher carbon stock and carbon sequestration.
Amount of carbon sequestered by all these tree species was positively correlated with organic carbon of their respective soils (r = 0.408).
Total biomass, carbon stock and carbon sequestration were significantly and positively correlated with height (r = 0.846**) and girth (r = 0.936**). Singh et al. (2022) also showed significant and positive correlation between height and girth increment and between biomass, carbon stock and carbon sequestration of tree species in his study of growth performance of fast-growing trees viz., Eucalyptus spp., Casuarina equisetifolia, Gmelina arborea and Melia dubia in high-density plantations in Prayagraj, Uttar Pradesh, India. In all the tree species, the amount of carbon sequestrated by individual tree species increased as the total biomass increased with the increase in age of tree. The increase in the amount of carbon sequestration was noticed with increase in girth. This is attributed to the fact that the trees with high diameter at breast height (DBH) may store about 1000 times more carbon than trees of low diameter at breast heights (Stoffberg et al., 2010). Irrespective of age the species has differ in their carbon sequestration potential due to their biomass production (Sangareswari et al., 2018). Increment in height of trees, biomass and carbon stock along the increase of its age was also reported by Balasubramanian et al. (2022). Annual increment in tree height, DBH, biomass and C storage was also reported by Kumar et al. (2020) and Ravula et al. (2022).
Table V. Ranges of growth parameters and carbon sequestration of various agroforestry tree species
Agroforestry tree plantation
|
Age
(years)
|
Height
range (m)
|
Girth
range
(m)
|
AGB
(kg tree− 1)
|
BGB
(kg tree− 1)
|
Total biomass
(kg tree− 1)
|
C stock
(kg tree− 1)
|
CO2 seq
(kg tree− 1)
|
Eucalyptus
|
5
|
8.5–10
|
0.23–0.44
|
6–27
|
2–7
|
8–34
|
4–17
|
15–62
|
7
|
8.4–12.5
|
0.28–0.55
|
9–53
|
2–14
|
12–66
|
6–33
|
21–122
|
10
|
12–16
|
0.48–0.77
|
39–132
|
10–34
|
49–167
|
24–83
|
89–306
|
15
|
14.2–20.3
|
0.70–1.12
|
97–355
|
25–92
|
122–447
|
61–224
|
224–821
|
Teak
|
5
|
6.3-7
|
0.22–0.33
|
5–12
|
1–3
|
6–15
|
3–7
|
11–27
|
10
|
9 -14.2
|
0.44–0.78
|
27–134
|
7–35
|
34–169
|
17–85
|
63–310
|
15
|
12–18
|
0.65–0.86
|
79–207
|
20–54
|
99–261
|
50–130
|
182–478
|
20
|
13–20
|
0.82–0.99
|
136–305
|
35–79
|
171–384
|
86–192
|
314–704
|
Malabar neem
|
5
|
12.8–14
|
0.56–0.77
|
51–105
|
13–27
|
64–133
|
32–66
|
118–243
|
8
|
13.2–18.5
|
0.64–0.85
|
69–169
|
18–44
|
86–214
|
43–107
|
158–392
|
Malabar neem
(MN + SW)
|
7
|
11.2–15.5
|
0.60–0.78
|
51–120
|
13–31
|
64–151
|
32–75
|
118–276
|
Sandalwood
(MN + SW)
|
7
|
5–6
|
0.42–0.61
|
21–53
|
5–14
|
26–67
|
13–33
|
48–122
|
Red sanders
|
5
|
6–8
|
0.25–0.35
|
7–19
|
2–5
|
9–24
|
5–12
|
17–44
|
7
|
7–9
|
0.34–0.45
|
16–36
|
4–9
|
20–45
|
10–22
|
37–82
|
10
|
9–15
|
0.47–0.95
|
39–264
|
10–69
|
49–333
|
24–167
|
90–611
|
Sandalwood
|
5
|
5.5–6.2
|
0.33–0.49
|
14–35
|
4–9
|
18–45
|
9–22
|
33–82
|
7
|
6.5–8.0
|
0.42–0.61
|
27–71
|
7–18
|
34–89
|
17–45
|
63–164
|
Subabul
|
5
|
5–7.5
|
0.25–0.48
|
5–27
|
1–7
|
6–34
|
3–17
|
11–63
|
8
|
11–15
|
0.38–0.60
|
25–85
|
6–22
|
31–107
|
16–53
|
58–196
|
10
|
13–21
|
0.55–0.88
|
62–256
|
16–66
|
78–322
|
39–161
|
143–591
|
MN + SW: Malabar neem + Sandalwood
Table VI. Growth parameters and carbon sequestration of agroforestry tree species
Tree plantation
|
Age
(years)
|
Height (m)
|
Girth
(m)
|
Total biomass
(kg tree− 1)
|
Carbon stock
(kg tree− 1)
|
CO2 seq.
(kg tree− 1)
|
Eucalyptus
|
5
|
8.87
|
0.34
|
18.7
|
9.4
|
34
|
Eucalyptus
|
7
|
10.50
|
0.42
|
34.2
|
17.1
|
63
|
Eucalyptus
|
10
|
14.10
|
0.62
|
100.5
|
50.2
|
184
|
Eucalyptus
|
15
|
17.00
|
0.94
|
273.8
|
136.9
|
502
|
Teak
|
5
|
6.53
|
0.29
|
10.7
|
5.3
|
20
|
Teak
|
10
|
12.47
|
0.62
|
96.7
|
48.4
|
177
|
Teak
|
15
|
15.00
|
0.74
|
165.3
|
82.7
|
303
|
Teak
|
20
|
16.83
|
0.89
|
261.7
|
130.8
|
480
|
Malabar neem
|
5
|
13.37
|
0.65
|
91.4
|
45.7
|
168
|
Malabar neem
|
8
|
16.00
|
0.75
|
146.7
|
73.3
|
269
|
Malabar neem (MN + SW)
|
7
|
13.23
|
0.73
|
114.3
|
57.1
|
210
|
Sandalwood
(MN + SW)
|
7
|
5.37
|
0.54
|
47.8
|
23.9
|
88
|
Red sanders
|
5
|
6.73
|
0.30
|
15.4
|
7.7
|
28
|
Red sanders
|
7
|
7.83
|
0.41
|
32.8
|
16.4
|
60
|
Red sanders
|
10
|
11.83
|
0.75
|
174.5
|
87.2
|
320
|
Sandalwood
|
5
|
5.80
|
0.42
|
31.6
|
15.8
|
58
|
Sandalwood
|
7
|
7.20
|
0.53
|
62.7
|
31.4
|
115
|
Subabul
|
5
|
6.47
|
0.36
|
17.4
|
8.7
|
32
|
Subabul
|
8
|
13.43
|
0.51
|
72.0
|
36.0
|
132
|
Subabul
|
10
|
16.97
|
0.71
|
176.1
|
88.0
|
323
|
S. E + m
|
0.55
|
0.03
|
11.3
|
5.6
|
20.7
|
CD
|
1.57
|
0.07
|
32.4
|
16.2
|
59.5
|
MN + SW: Malabar neem + Sandalwood |