Agroforestry Chapter 4 (Part 3): Energy Plantations
Agroforestry Notes · Chapter 4 · Part 3
Chapter 4 (Part 3): Energy Plantations
Why India needs fuelwood plantations, criteria and species for energy plantations, charcoal, petro-crops and extractives, calorific value, advantages, and the species table of specific gravity and calorific value.
1. The fuelwood problem
Most of India’s rural people depend on wood for cooking. The e-course gives these figures:
Firewood use is more than 133 million tonnes a year, mostly for cooking.
Cooking 1 kg of food needs about 1.2 kg of firewood, so India must grow more wood than food.
About 400 Mt of cattle dung, equal to about 60 Mt of fuelwood, is burnt every year instead of going to the fields.
Fuelwood collection is the most significant reason for tree cutting.
An energy plantation is grown purely to produce plant material for fuel rather than for fibre. Growing fuelwood on farms through agroforestry saves natural forests and returns dung to the soil.
2. Criteria and species
Criteria for energy plantation species
- Fast growth and high photosynthetic efficiency.
- High coppicing and pollarding ability, so the stand can be cut again and again.
- Conical or cylindrical crown shape.
- Wood of high calorific value and density, burning without sparks or toxic smoke.
- Tolerance to pests and diseases; low transpiration in arid areas.
- Nitrogen fixation if possible, and multiple uses.
| Region | Species |
|---|---|
| Tropical dry | Acacia catechu, A. nilotica, A. senegal, A. tortilis, Anogeissus pendula, Albizia lebbek, Azadirachta indica, Cassia siamea, Dalbergia sissoo, Eucalyptus camaldulensis, Gmelina arborea, Pongamia pinnata, Prosopis cineraria, P. juliflora, Tamarindus indica, Tecomella undulata, Ziziphus mauritiana |
| Tropical humid | Acacia auriculiformis, A. nilotica, Albizia procera, Casuarina equisetifolia, Dalbergia sissoo, Dendrocalamus strictus, Eucalyptus, Leucaena leucocephala, Melia azedarach, Gliricidia sepium, Gmelina arborea, Syzygium cumini |
| Sub-tropical | Acacia catechu, A. nilotica, Ailanthus excelsa, Celtis australis, Grevillea robusta, Populus deltoides, Robinia pseudoacacia, Salix alba, Toona ciliata |
| Temperate | Acer, Aesculus indica, Alnus nepalensis, A. nitida, Celtis australis, Quercus semecarpifolia, Salix alba, Toona serrata |
| Shrubs | Dodonaea viscosa, Jatropha curcas, Clerodendron inerme, Ipomoea carnea, Tecoma |
3. Charcoal, petro-crops and extractives
Burning firewood directly in crowded areas causes smoke and pollution; converting it to charcoal is cleaner and more efficient.
1 kg charcoal = 2.38 kg firewood or more.
Combustion efficiency of charcoal is about 28%.
Sulphur-free reductant in electrometallurgy; used for calcium carbide, carbon disulphide and activated carbon.
Acacia nilotica, Adina cordifolia, Anogeissus latifolia, Casuarina equisetifolia, Pinus roxburghii, Quercus leucotrichophora, Q. semecarpifolia, Tamarindus indica, Terminalia spp.
Plants that yield energy-rich exudates and extractives that can replace petrochemicals are called “petro-crops”. Extractive plants yield latex, vegetable oils and waxes, resins, essential oils, and tannins/phenolics.
| Extractive | Details |
|---|---|
| Latex | Families Apocynaceae, Asclepiadaceae, Euphorbiaceae, Moraceae, Sapotaceae. Petro-crops: Euphorbia antisyphilitica, E. tirucalli, E. lathyris, Pedilanthes tithymaloides, Calotropis procera, Asclepias curassavica, Parthenium argentatum (guayule) |
| Vegetable oils | Can be blended with diesel; non-edible oil trees suit wastelands: Jatropha curcas, Pongamia pinnata, neem, Madhuca, Calophyllum inophyllum, Simmondsia chinensis (jojoba), Sapium sebiferum, Schleichera oleosa |
| Resins | Mainly Pinaceae: volatile turpentine and non-volatile rosin; turpentine is highly combustible |
4. Calorific value and advantages
Calorific value is the amount of heat produced when 1 g of fuel is completely burnt in excess air or oxygen. A fuel with high calorific value is a good fuel.
Little or no sulphur and less NO₂ than fossil fuels.
Growing plants absorb about as much CO₂ as is released when they burn; roots store carbon underground.
Rehabilitate degraded and marginal lands; rural employment.
Lower energy cost per unit area than agricultural crops; nutrients can be returned as ash.
Windbreaks, shelterbelts, fodder, NTFP and aesthetic value.
| Species | Specific gravity | Calorific value (kcal/kg) |
|---|---|---|
| Acacia catechu | 1.00 | 5142–5244 |
| Acacia nilotica | 0.67–0.68 | 4800–4950 |
| Albizia lebbek | 0.55–0.64 | 5163–5166 |
| Anogeissus latifolia | 0.94 | 4948 |
| Casuarina equisetifolia | 0.80–1.2 | 4950 |
| Dalbergia sissoo | 0.75–0.80 | 4908–5181 |
| Dodonaea viscosa | 1.20–1.28 | 4939–5035 |
| Eucalyptus tereticornis | 0.70 | 4800 |
| Hardwickia binata | 1.08 | 4891–4952 |
| Leucaena leucocephala | 0.55–0.70 | 4200–4600 |
| Prosopis juliflora | 0.70 | 4800 |
| Quercus leucotrichophora | 0.74 | 4633 |
| Shorea robusta | 0.68–0.82 | 5095–5433 |
| Tectona grandis | 0.55–0.70 | 4989–5535 |
| Alnus nepalensis | 0.32–0.37 | 4600 |
| Trema orientalis | 0.48 | 3095 |
5. Fuelwood in Nair: “the other energy crisis”
Eckholm (1975) called the fuelwood shortage “the other energy crisis”. About 1.5 billion people met at least 90% of their energy needs from wood, and another 1 billion at least 50%.
- Many fuelwood projects gave poor results (Floor, 1987). Farmers preferred multipurpose trees and sold poles rather than burning them.
- Gujarat social forestry in the 1980s mostly produced poles and pulpwood, not fuel (Foley and Barnard, 1984).
- Markets prefer particular woods: Combretum in Niger; Acacia nilotica, tamarind and Prosopis in India.
- Fuel gathering is mostly women’s work. People facing shortage switch to crop residues and dung instead of buying wood, so Nair treats fuelwood as a subsidiary benefit of multipurpose trees, not the only aim.
Putting a price on fuelwood: Nepal (Gregersen et al., 1989)
When fuelwood is short, farmers burn cattle dung, and that dung is then lost as manure. The value of fuelwood can be worked out from the maize lost:
6. Quick revision box
- Firewood use >133 Mt; 1.2 kg wood per kg food; 400 Mt dung ≈ 60 Mt fuelwood.
- Energy plantation species: fast-growing, coppicing, high CV and density, conical crown, N-fixing.
- Charcoal: 1 kg = 2.38 kg firewood; efficiency 28%; sulphur-free.
- Petro-crops: Euphorbia, Calotropis, Parthenium argentatum (guayule).
- Latex families: Apocynaceae, Asclepiadaceae, Euphorbiaceae, Moraceae, Sapotaceae.
- Resins: Pinaceae (turpentine + rosin).
- CV: carbon 30 kJ/g; hydrogen 150 kJ/g.
- Acacia catechu sp. gr. 1.00, CV 5142–5244 kcal/kg.
- Eckholm (1975): “the other energy crisis”; 1.5 billion people ≥90% energy from wood.
- Fuelwood 4,700 kcal/kg vs dung 2,400; Nepal: 1 m³ fuelwood ≈ NRs 520 of maize.
7. Interactive MCQ Quiz
20 questions. Tap an option to see the answer and explanation, then go to the next question.
Comments
Post a Comment