• Energy Research

Climate change, land degradation, and desertification lead to the loss of carbon present in the soil and plants. The carbon dioxide (CO2) concentration in the atmosphere has reached 412 ppm. This is a rise of 47% since the start of the industrial period, when the concentration was close to 280 ppm. Therefore, the sequestration of carbon from the atmosphere to earth is the need of the hour. Many scientists have suggested agroforestry as a potent instrument for climate change mitigation as well as to fetch lucrative benefits. The Indian government is also promulgating tree-based systems for increasing tree cover up to 33% of the total geographical area to mitigate climate change. Therefore, the expansion of the commercial agroforestry system of fast-growing tree species producing higher biomass could be a sustainable and ecologically benign technique to sequester carbon, increase green cover, and improve the financial status of farmers. This review highlights the commercial agroforestry systems, biomass and carbon sequestration potential, and case studies of poplar and eucalyptus. The species such as poplar (Populus deltoides), nilgiri (Eucalyptus spp.), subabul (Leucaena leucocephala), tree of heaven (Ailanthus excelsa), willow (Salix spp.), malabar neem (Melia dubia), cadamba (Neolamarckia cadamba), and white teak (Gmelina arborea) are the suitable tree species for carbon sequestration under agroforestry. Among these species, poplar and eucalyptus are major agroforestry tree species that have been adopted by millions of farmers in India since the 1990s. Indo-Gangetic plains are considered the birthplace of commercial or industrial agroforestry, as poplar and eucalyptus are widely planted. This review reports that poplar and eucalyptus have the potential to sequester carbon stock of 212.7 Mg C ha−1 and 237.2 Mg C ha−1, respectively. Further, the net carbon sequestration rate in poplar and eucalyptus was 10.3 and 12.7 Mg C ha−1 yr−1, respectively. In conclusion, the commercial agroforestry system was very successful in the Indo-Gangetic regions of the country but needs further expansion with suitable compatible crops in different parts of the country.

Poplar is popular among farmers and planted widely in the form of block and boundary systems. The preferences of farmers are shifting much more towards bund plantations due to their smaller yield reductions and can take up kharif and rabi crops till rotation. As for boundary plantations, farmers tend to grow trees in any direction without concern for yield reduction or profitability. Against this background, an experiment was designed by planting poplar at 2 m intervals in East–West (E–W) and North–South (N–S) directions during 2008 to determine the production potential and economic viability of boundary plantations and their effect on sorghum (Sorghum bicolor) and wheat (Triticum aestivum) crop rotations till harvesting of the trees. The experiment comprised three variables: stand age (years); four aspects (northern and southern E–W rows, eastern and western N–S rows; these four aspects are considered by dividing the tree lines); and six distances from tree the lines (0–3, 3–6, 6–9, 9–12, 12–15, 15–18 m and a control). A split-split plot design with three replicates was used. A significant reduction of fodder biomass of sorghum and wheat yield was observed up to 9 m distant from the tree line: the reduction was 10 to 60% for the kharif season and 7.2 to 29.5% for rabi crops from the second year to eight years after planting, respectively. Interestingly, the poplar boundary plantation had a favorable microclimatic effect from 9 to 15 m distance from the tree line, which increased crop yields compared with the control. The total dry wood production of poplar in the E–W direction (166.99 mg ha−1) was almost two times more than production for the N–S direction (82.62 mg ha−1) at 8 years of rotation. The economic analysis of this study concluded that an E–W boundary plantation of poplars exhibited the maximum net returns of INR 549,367 ha−1, a net present value of INR 222,951 ha−1, a BC ratio of 1:1.65, an IRR of 85% and an LEV of INR 1,220,337 ha−1. Therefore, it is concluded that the intercropping of a sorghum-wheat crop rotation in E–W boundary plantations was more beneficial for enhancing farm income over traditional agriculture in north India.

Agroforestry integrates woody perennials with arable crops, livestock, or fodder in the same piece of land, promoting the more efficient utilization of resources as compared to monocropping via the structural and functional diversification of components. This integration of trees provides various soil-related ecological services such as fertility enhancements and improvements in soil physical, biological, and chemical properties, along with food, wood, and fodder. By providing a particular habitat, refugia for epigenic organisms, microclimate heterogeneity, buffering action, soil moisture, and humidity, agroforestry can enhance biodiversity more than monocropping. Various studies confirmed the internal restoration potential of agroforestry. Agroforestry reduces runoff, intercepts rainfall, and binds soil particles together, helping in erosion control. This trade-off between various non-cash ecological services and crop production is not a serious constraint in the integration of trees on the farmland and also provides other important co-benefits for practitioners. Tree-based systems increase livelihoods, yields, and resilience in agriculture, thereby ensuring nutrition and food security. Agroforestry can be a cost-effective and climate-smart farming practice, which will help to cope with the climate-related extremities of dryland areas cultivated by smallholders through diversifying food, improving and protecting soil, and reducing wind erosion. This review highlighted the role of agroforestry in soil improvements, microclimate amelioration, and improvements in productivity through agroforestry, particularly in semi-arid and degraded areas under careful consideration of management practices.