Carbon emission, sequestration, credit and economics of wheat under poplar based agroforestry system

Abstract

The present study was conducted to compare the carbon sequestration potential, carbon emission, and cost benefit ratio of wheat varieties under open farming and poplar based agroforestry system. Field experiment was carried out at Agroforestry Research Center, G.B. Pant University of Agriculture and Technology, Pantnagar, India. The experimental plots were laid out in randomized block design (RBD) with two associate farming systems, open farming and poplar based agroforestry system, and four varieties of wheat, PBW-373, PBW-343, UP-262 and VL-907, with three replications. Above ground, below ground and total biomass, carbon stock, carbon sequestration, carbon credit, and carbon price all were significantly higher in wheat under poplar based agroforestry system (22.949, 2.753, 25.702, 11.460, 42.049 tonnes/ha, 40.049 and $744.270/ha) while net emission was significantly lower (−40.998 tonnes/ha) in two years, as compared to open farming (−37.263 tonnes/ha). Net return and Benefit Cost (B:C) ratio ($876.29/ha and 1.83) was also higher in agroforestry system than open farming system ($700.91/ha and 1.82). Among wheat varieties VL-907 recorded maximum net return and B:C ratio ($914.52/ha and 2.12) followed by PBW-343.

Keywords:

• Carbon emission
• carbon sequestration
• carbon stock
• carbon credit
• economics

Introduction

Agroforestry is the science of designing and developing integrated, self-sustainable, land-management systems that involves the introduction and retention of woody components such as trees, shrubs, bamboos, canes and palms along with agricultural crops including pastures or animals, simultaneously or sequentially on the same unit of land and time, to satisfy the ecological as well as socio-economic needs of people. Agroforestry provides assets and income from wood energy, diversified crop rotations, improved soil fertility, enhancement of local climatic conditions, ecosystem services and reduces human impacts on natural forests [1,2]. The ever-increasing demand for wood products could be minimized by growing timber trees in agriculture landscape. Various fast-growing and industrially important tree species like poplar, eucalyptus, melia, shisham and bamboo can be grown under agroforestry system [3,4].

Total green cover under agroforestry system of the country is estimated at 111,554 km² which is 3.39 percent of country’s total geographical area, out of which poplar, which is one of the fastest-growing industrial soft woods, is extensively planted on an area of 2700 km² in northern India [5] and covers 1.22% of the total area under agroforestry [6]. Poplar (Populus deltoids Bartr.) based agroforestry system is economically viable and more sustainable than many other crop rotations prevalent in northern and eastern India since mid-80s [7]. Its popularity among the farmers is mainly due to multi-utility wood, fast growth, high market prices, less competition with associated crops and pruning tolerant nature [8]. Many research findings have highlighted that the benefits of intercropping in poplar could be more money spinning than growing crops as monocropping [3,5,9–11]. An average farmer earns 46% higher income from poplar-based agroforestry system [12]. Studies revealed that Poplar based agroforestry system increases income (>70%) and is an emergency source of cash (>20%) for plantation owner in northern India [13]. Poplar, being a fast-growing tree, also provides vast opportunities for carbon (C) sequestration.

Wheat (Triticum aestivum L.) is grown extensively under agroforestry system in central and northern India. Poplar, due to its leaf shedding habit before sowing of wheat in winter season, makes an excellent companion tree than other tree interfaces and higher wheat yield under poplar compared to other tree-crop in agroforestry system is reported due to its complementary effects on resource allocation [14,15]. The inherent potential of wheat under poplar based intercropping system can be achieved by enhancing the competitive ability of wheat through appropriate and sustainable land use system. Keeping these points in view, an experiment was aimed to assess the performance of wheat varieties under sole cropping and poplar based agroforestry system. The present study also compared the C sequestration potential and cost benefit of wheat under open and poplar based agroforestry system in Pantnagar, Uttarakhand, India. Carbon studies are gaining importance as there are various negative environmental impacts of conventional farming, agriculture contributing nearly 14% and land use and forestry 17% of the Greenhouse Gases (GHGs) emissions globally. Increasing carbon emissions is the major concern now days and to minimize the carbon emissions through sequestering more carbon in system is one way to mitigate climate change and achieve the global targets of reducing the emission intensity of its gross domestic product (GDP). Government of India has set a goal to reduce emissions upto 33–35% from 2005 level and to create an additional carbon sink of 2.5–3.0 billion tonnes of carbon dioxide (CO₂) equivalent through additional forest and tree cover by 2030 under Intended Nationally Determined Contribution (INDC) submitted to United Nations Framework Conservation on Climate Change (UNFCCC). Efforts are made to generate data on potential of different tree species under systems for carbon sequestration in different regions.

Methods

Site description and experimental setup

The study was conducted during winter season of 2013–14 at the experimental site of Agroforestry Research Centre of G.B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand (29° 1' 21"N to 29° 1' 43"N Latitude and 79° 24' 19"E to 79° 24' 30"E longitudes and at an altitude of 243.84 meters), which lies in the foothills of the Shivalik range of the Himalayas and North West plain agro-climatic wheat zone in the narrow strip called ‘Terai’. The experiment was laid out in randomized block design with two-factors, two systems, viz. open farming and poplar based agri-silvicultural system, and four varieties of wheat viz. PBW-343 (timely sown), PBW-373 (late sown), UP-262 (early sown), VL-907 (late sown) with high yield potentials, and replicated thrice. The poplar clone G-48 was used which is fast growing and shed leaves during four winter months, and hence is suitable for this region under agroforestry conditions. Plot size was 7 × 6 m² and the spacing of Poplar was 7 m × 3 m. Poplar seedlings were transplanted in the experimental field on February 22, 2012. Different varieties of wheat were sown mechanically in rows at a distance of 23.0 cm on November 14, 2013; seed rate was 100 kg per hectare. The land was left fallow during summer season. The experimental layout is shown in Figure 1.

Figure 1. Layout plan of the field experiment under open farming system and poplar based agroforestry system.

Plant sampling and carbon sequestration

Poplar plantations of clone G-48 (2 year old) trees were measured for their height from ground to top of the trees and girth at breast height (1.37 m above the ground level). Standing volume of timber tree was calculated by the regression equation: Total volume (m³) V = 0.003487 + 0.268366 × D²H, where, V, D and H represent timber volume, diameter at breast height and height of the tree, respectively [16]. The above ground biomass of poplar was calculated by the formula: Biomass = volume X specific gravity of wood (0.423 g/cm³ for G-48 clone of poplar [17]. The below ground biomass of poplar was calculated using IPCC, default value 0.26 [18]. Therefore, carbon storage of poplar tree has been computed by fraction of biomass, i.e. C = 0.42 × B, (C content in percentage equal to 42 for poplar tree [19]) where C is the carbon stock and B the dry biomass. Above ground and below ground carbon stock in herbs and shrub species was determined by multiplying their respective aboveground and belowground biomass with carbon conversion factor of 0.45 [20]. The estimated carbon stocks were converted into CO₂ equivalents (quantity of C × 44/12 or 3.66) for calculating CO₂ assimilation by biomass of poplar trees in agroforestry systems. The carbon credit or certified emission reduction (CER) is the unit related to reduction of 1 tonnes of CO₂ emission. The value of one carbon credit or CER in US Dollar is about 17.7 $.

Carbon emission

The carbon (CO₂ -e) emission was estimated by “Green House Gases Estimation Tool for Integrated Farming System Models” developed by ICAR-Indian Institute for Farming System Research, Modipuram, Meerut, India. All the inputs used, viz. diesel used for land preparation, irrigation, and running of any other farm machinery, fertilizers, agrochemicals etc. were taken into account as for the estimation of CO₂ -e emission. Net emission was then calculated by subtracting total carbon sequestered in the field from total CO₂ -e emission from the field.

Grain, straw and biological yield

Yield of wheat was recorded by harvesting the net plot area of each plot at physiological maturity. Harvests were then left to dry and then threshed and winnowed to get grain and straw yield separately. To estimate the biological yield of wheat, plants were uprooted to the depth possible in 1 m² area. Fresh weight (above and below ground) was taken and hereafter, the representative samples from all treatment and replications were taken and brought to laboratory and dried in oven at 60 °C till the constant weight was attained to record dry weight.

Economic analysis of poplar-based agroforestry systems

In economics, cost of cultivation is the total expenditure incurred right from sowing to harvest of the crop, including the field preparation. It is worked out from cost of input materials such as seeds, fertilizers, insecticides, pesticides, etc and labor cost for total man days needed, and is expressed in $/ha. Gross return is the total income obtained by selling price of main product as well as by products and is also expressed in $/ha. Market price helps portray the economic overview of agroforestry systems.

Net return

Net return is obtained by subtracting cost of cultivation from gross return and expressed in $/ha. The Net return calculated as follows

Net Return = Gross return – Total cost of cultivation

Benefit cost ratio

Benefit Cost Ratio (BCR) is the ratio of net return and cost of cultivation. It can be expressed as under $$\text{Benefit Cost Ratio}(\text{BCR})=\frac{\text{Net return }\left(\$/\text{ha}\right)}{\text{Cost of cultivation }\left(\$/\text{ha}\right)}$$

The project is considered to be viable only when BCR is one or more than one.

Statistical analysis

Whole data was first entered in Microsoft excel and then analyzed by OP-STAT software. Significance of variance was determined using ANOVA and summaries were drawn. Standard error of mean (SEm±) and C.V. was computed in each case by using the critical difference (C.D.) at 5% probability level to test the effects of treatments.

Results and discussion

Growth parameters of poplar tree

Growth and biomass of poplar tree in open farming and poplar based agroforestry system are presented in Table 1. Mean dbh, height and volume of poplar tree were found to be 6.36 cm 5.27 m and 0.0146 m³ respectively, the total biomass (aboveground and belowground), carbon stock, carbon sequestration were estimated to be 3.707, 1.597, and 5.862 tonnes/ha respectively and the Carbon credit and Economic price were found to be 5.86 and $103.76 at the age of two years.

Table 1. Growth parameters of poplar tree at the end of experiment (two years old).

Tree No.	Diameter at breast height (cm)		Plant height (m)	Tree volume (m^3)	Total Biomass (tonnes/ha)	Carbon stock (tonnes/ha)	Carbon sequestration (tonnes/ha)	CER or Carbon credit	Economic price ($ or Dollar)
1	7.32		5.00	0.0156	3.958	1.662	6.100	6.10	107.98
2	6.36		3.60	0.0141	3.577	1.502	5.514	5.51	97.59
3	4.13		5.10	0.0098	2.486	1.044	3.832	3.83	67.83
4	5.72		5.45	0.0118	2.994	1.257	4.614	4.61	81.67
5	7.95		6.5	0.0202	5.125	2.152	7.899	7.90	139.82
6	6.68		5.00	0.0142	3.603	1.513	5.553	5.55	98.29
7	4.77		4.50	0.0105	2.664	1.119	4.106	4.11	72.68
8	8.27		5.70	0.0207	5.252	2.206	8.095	8.09	143.28
9	7.00		5.10	0.0157	3.983	1.673	6.139	6.14	108.67
10	6.68		6.20	0.0145	3.679	1.545	5.670	5.67	100.36
11	5.72		4.60	0.0119	3.019	1.268	4.654	4.65	82.37
12	6.50		5.50	0.0145	3.679	1.545	5.670	5.67	100.36
13	3.82		4.70	0.0091	2.309	1.854	6.804	6.80	120.44
14	5.41		5.50	0.0122	3.095	1.300	4.771	4.77	84.44
15	7.63		6.50	0.0192	4.871	2.046	7.508	7.51	132.89
16	7.62		6.00	0.0182	4.617	1.939	7.117	7.12	125.97
17	6.61		5.50	0.0173	4.389	1.843	6.765	6.77	119.74
18	6.36		4.80	0.0133	3.374	1.417	5.201	5.20	92.06
19	7.00		5.80	0.0162	4.110	1.726	6.335	6.34	112.13
20	7.32		5.70	0.0169	4.288	1.801	6.609	6.61	116.98
21	7.32		5.60	0.0167	4.237	1.779	6.531	6.53	115.59
22	3.82		3.70	0.0089	2.258	0.948	3.480	3.48	61.60
Mean		6.36	5.27	0.0146	3.707	1.597	5.862	5.86	103.76

Carbon sequestration

Above ground, below ground, and total biomass, carbon stock, carbon credit as well as economic price all were significantly higher in wheat under agroforestry system (22.949, 2.753, 25.702, 1.146 tonnes/ha, 42.049 and $744.270) as compared to open farming (Table 2) due to tree biomass in addition to wheat under agroforestry system. Tandon et al. [21] also reported estimated bole biomass of 17.42, 37.47 and 47.80 tonnes/ha at the age of 3, 5 and 7 years respectively of Poplar deltoids trees planted in agroforestry with a spacing of 5 m × 5 m (400 trees/ha). Among wheat varieties, VL-907 recorded maximum above ground, below ground and total biomass, carbon stock, carbon credit as well as economic price (23.199, 2.540, 25.739, 11.531 tonnes/ha, 42.317 and $749.01) followed by PBW-343 and minimum was found in UP-262 (21.278, 2.379, 23.657, 10.586 tonnes/ha, 38.851 and $687.67).

Table 2. Total biomass, carbon stock, CER and carbon price at the end of experiment (two years) under open farming and poplar based agroforestry system.

Treatments	Biomass (Trees + Wheat) (tonnes/ha)			Carbon stock (tonnes/ha)	CER or Carbon credit	Carbon price ($ or Dollar)
	Above ground	Below ground	Total
Farming systems
Open farming	21.061	2.106	23.167	10.425	38.261	677.220
Agroforestry system	22.949	2.753	25.702	1.146	42.049	744.270
SEm ±	0.404	0.049	0.451	0.194	0.712	12.592
CD (5%)	1.225	0.148	1.367	0.588	2.158	38.195
Wheat varieties
PBW-343	22.226	2.443	24.669	11.049	40.550	717.73
PBW-373	21.317	2.357	23.674	10.600	38.902	688.57
UP-262	21.278	2.379	23.657	10.586	38.851	687.67
VL-907	23.199	2.540	25.739	11.531	42.317	749.01
SEm ±	0.571	0.069	0.637	0.274	1.006	17.808
CD (5%)	NS	NS	NS	NS	NS	NS
Interaction	NS	NS	NS	NS	NS	NS
CV %	6.356	6.957	6.391	6.453	6.454	6.453

Net carbon emission

The net carbon emission per ha in two years was significantly lower in agroforestry system (−40.998 tonnes/ha) as compared to open farming (−37.263 tonnes/ha) in spite of higher emission (1.052 tonnes/ha as compared to 0.998 tonnes/ha in open farming) due to more carbon sequestered by trees in the system (42.049 tonnes/ha as compared to 38.261 tonnes/ha in open farming). Among wheat varieties, VL-907 recorded minimum net carbon emission (−41.292 tonnes/ha) followed by PBW-343 (−39.525 tonnes/ha) and maximum was found in UP-262 (−37.827 tonnes/ha), showed in Table 3. The carbon sequestration of wheat varieties under open farming and total carbon sequestered by wheat varieties and poplar tree under agroforestry system and subsequent net emission in both the system is graphically presented in Figure 2.

Figure 2. Carbon sequestration and net emission at the end of experiment (two years) under open farming and poplar based agroforestry system.

Table 3. CO₂-e emission, carbon sequestration and net emission at the end of experiment (two years) under open farming and poplar based agroforestry system.

Treatments	CO2-e emission (tonnes/ha)	Carbon sequestration (tonnes/ha)	Net emission (tonnes/ha)
Farming systems
Open farming Agroforestry system SEm ± CD (5%)	0.998	38.261	−37.263 −40.998 0.711 2.158
	1.052	42.049
	–	0.711
	–	2.158
Wheat varieties
PBW-343 PBW-373 UP-262 VL-907 SEm ± CD (5%)	1.025	40.550	−39.525 −37.877 −37.827 −41.292 1.006 NS
	1.025	38.902
	1.025	38.851
	1.023	42.317
	–	1.006
	–	NS
Interaction	–	NS	NS
CV %	–	6.453	6.631

Soil organic carbon

Initial soil organic carbon at the time of tree planting was recorded to be 0.96% in 0–15 cm and 0.80% in 15–30 cm of soil layer. After two years of experimentation, soil organic carbon in all the treatments increased in both the layers. This increase can be attributed to addition of biomass in the soil as a result of farming. Agroforestry system recorded higher increase than open farming due to total leaf fall of poplar trees in winter season and leaves are easily decomposed in the soil. Soil organic carbon under poplar-based agroforestry system and open farming was 1.12% and 1.04% in 0–15 cm layer and 0.86% and 0.81% in 15–30 cm layer, respectively. Among wheat varieties, soil organic carbon was found maximum in the wheat variety PBW-343, followed by VL-907, UP-262 and PBW-373 as shown in Table 4. Addition of litter fall and fine-root in the soil turnover increased soil organic matter content. Sharma and Dadhwal [22] estimated that poplar leaf litter added on an average in the soil at the age of 3–4 year. Near poplar tree line (0–3 m) higher organic carbon (0.53%) contents were recorded. Gupta et al. [23] also recorded increase in average soil organic carbon from 0.36% in sole crop to 0.66% in 1, 3 and 6 years old poplar based agroforestry soils.

Table 4. Initial (February, 2012) soil organic carbon (%) in open farming and final (April, 2014) wheat under open farming and poplar based agroforestry system.

Treatments	Organic carbon (%) (Final)
	0–15 cm	15–30 cm
Farming systems
Open farming	1.04	0.81
Agroforestry system	1.12	0.86
SEm ±	0.01	0.01
CD (5%)	NS	NS
Wheat varieties
PBW-343	1.14	0.84
PBW-373	1.01	0.82
UP-262	1.05	0.78
VL-907	1.12	0.89
SEm ±	0.01	0.01
CD (5%)	0.04	0.01
Interaction	NS	NS
CV %	3.01	3.91
Initial	0.96	0.80

Economics

Economics of poplar based agroforestry was calculated for open farming and agroforestry system on the basis of selling rates of different produces (Poplar – $86.67/tonnes, Wheat grain – $240/tonnes and Wheat straw – $26.67/tonnes) and are presented in Table 5. The net return and B:C ratio are found higher in agroforestry system ($876.29/ha and 1.83) than open farming ($700.91/ha and 1.82). Among wheat varieties, VL-907 recorded significantly higher net return and B:C ratio ($914.52/ha and 2.12) followed by PBW-343 ($825.88/ha and 1.91) and minimum was found in UP-262 ($665.20/ha and 1.56). Singh et al. [24] and Kumar et al. [25] also reported higher net returns from agri-silviculture system of poplar (500 trees/ha) with wheat in winter and fallow in rainy season in northern India.

Table 5. Economics under open and poplar based agroforestry system.

Treatments	Wheat yield (tonnes/ha)		Gross return ($ or Dollar)			Net return($)	B:C ratio
	Grain yield	Straw yield	Wheat	Tree	Total
Farming systems
Open farming	3.790	6.595	1085.41	0	1085.41	700.91	1.82
Agroforestry system	3.674	6.445	1053.65	305.60	1359.25	876.29	1.83
SEm ±	0.254	0.403	8.15	10.24	13.00	13.00	0.03
CD (5%)	NS	NS	24.95	31.35	39.84	39.84	NS
Wheat varieties
PBW-343	39.09	6.423	1109.36	150.25	1259.61	825.88	1.91
PBW-373	36.04	6.128	1038.43	154.12	1182.53	748.80	1.72
UP-262	31.98	6.554	942.36	156.57	1098.93	665.20	1.56
VL-907	42.17	6.975	1198.01	150.25	1348.25	914.52	2.12
SEm ±	3.59	0.570	11.52	14.48	18.40	18.40	0.04
CD (5%)	NS	NS	35.28	NS	56.33	56.33	0.12
Interaction	NS	NS	NS	NS	NS	NS	SEm ± 0.05 CD (5%)0.17
CV %	6.93	6.27	11.97	9.81	11.54	13.39	12.11

Conclusion

Poplar based agroforestry system recorded higher biomass production, resulting in higher carbon stock, carbon sequestration and certified emission reduction and subsequently lower net emission than open farming, which are major environmental goals to reduce the emissions from farming sector. In addition to these environmental benefits, wheat under agroforestry also increased soil organic carbon due to litter fall and gave higher monetary returns in terms of net return, B:C ratio and carbon price ($876.29/ha, 1.83 and $744.27/ha) than under open farming. Among wheat varieties VL-907 recorded maximum net return and B:C ratio ($914.52/ha and 2.12) followed by PBW-343. It can thus be concluded that the impacts of greenhouse gases, global warming and climate change as a whole can be reduced or improved through agroforestry, making agricultural production systems more profitable as well. In general, trees also improve above and below ground microclimate, meso and microfauna, and microflora around plant roots which alter soil chemical, biological, and physical properties.

Acknowledgments

This research partly formed the M.Sc. Agriculture (Agroforestry) thesis by the first author, and for field and laboratory facilities provided, Chairman & HOD, Department of Agroforestry, College of Agriculture, G. B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India are gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).