Converting primary forests to cultivated lands: Long-term effects on the vertical distribution of soil carbon and biological activity in the foothills of Eastern Himalaya.

The conversion of primary forests to cultivation brings a significant change in soil carbon (C) forms. In the foothills of the Eastern Himalayan Region of India (Manipur), such conversions are prevalent. However, little is known about the response of C forms, particularly in deep soil, to land use conversion in the region. We evaluated changes in soil C forms (total organic, inorganic, and pools) and microbiological properties (up to 1.0 m depth) mediated by C when the 45-year-old forest had been cultivated for 18-25 years. The cultivated land uses were tree-based agroforestry (LAF: legumes, NAF: non-legumes), horticultural fruits (WHF: woody, NHF: non-wood, mainly vegetables), and paddy agriculture system (AUS: upland, ALS: lowlands). Forest conversion significantly (p < 0.05) decreased the total carbon (TC) in the surface soil (0.0-0.15 m) from 4.88 % to 3.04-3.93 % in the tree-based land uses (LAF, NAF, and WHF). TC further declined to 2.05-2.81 % under seasonal crops (NHF, AUS, and ALS). Seasonal crop cultivation also caused a higher decline in microbial biomass carbon, soil enzymes, and carbon pools (active and passive) than the tree-based land use with the soil depth. The vertical distribution of C in the soil profile was inconsistent: organic C (including C pools) decreased, while inorganic C increased. The profile TC stock to a depth of 1.0 m in the forest was 358.8 Mg ha-1, of which 81 % were organic C, and 19 % were inorganic C. In comparison with forest soil, total soil C stocks (organic and inorganic) decreased more (-44.1 to -55.1 %) in seasonal crops than in tree-based (-15.4 to -36.3 %) land uses. The degradation index (DI) also confirmed that seasonal crop cultivation caused a larger decline in surface soil quality (DI: -423 % to -623 %) than tree-based land use (DI: -243 % to -317 %). The topsoil (up to 0.45 m) of seasonal crops was more degraded than that of the subsoil (>0.45 m-1.0 m). Forests converted to seasonal cultivation (upland rice and vegetables) caused higher degradation of soil C forms and overall soil health in the Himalayan foothills of northeastern India. We suggest the promotion of Agroforestry based on legumes (Parkia spp.) and woody fruits (mango/citrus/guava) in the uplands to minimize soil C degradation while ensuring nutritional security in the hill agro-ecosystems of the Indian Himalayas.

Energy and carbon budgeting of traditional land use change with groundnut based cropping system for environmental quality, resilient soil health and farmers income in eastern Indian Himalayas.

Energy intensive traditional cereals based monoculture often lead to high greenhouse gas emissions and degradation of land and environmental quality. Present study aimed at evaluating the energy and carbon budget of diversified groundnut (Arachis hypogea L) based cropping system with over existing traditional practice towards the development of a sustainable production technology through restoration of soil and environmental quality and enhancement of farming resiliency by stabilizing farmers' income. The trials comprised of three introduced groundnut based systems viz. groundnut- pea (Pisum sativum), groundnut-lentil (Lens esculenta) and groundnut-toria (Brasssica campestris var. Toria) replacing three existing systems viz. maize (Zea mays L) - fallow, maize - toria, and rice (Oryza sativa L)-fallow systems. Four years study revealed that adoption of groundnut based systems reduced non-renewable energy input use (fertilizers, chemical, machinery and fossil fuels) by 25.5%, consequently that reduced the cost of production. Repeated analysis of variance measurement also affirmed that groundnut based systems (groundnut-pea>groundnut-lentil> groundnut-toria) increased the energy use efficiency, energy productivity, carbon use efficiency, net returns and decreased the specific energy and energy intensiveness. Groundnut based systems increased the mean system productivity and water productivity in terms of groundnut equivalent yield by 3.7 and 3.1 folds over existing practice. The savings of fossil fuel reduced greenhouse gas emissions owing to reduced use of farm machinery and synthetic fertilizers. Groundnut based systems significantly (p < 0.05) enhanced the soil carbon concentration (8.7-18.1%) and enzymatic activities (27.1-51.8%) over existing practice. Consequently, estimated soil quality index values were 35.9-77.3% higher under groundnut based systems than existing practice. Thus, the study indicated the resilient nature of groundnut based systems as an environmentally safe and sustainable production technology for enhancing resource use efficiency, reduce carbon emission, energy intensiveness and cost of production in the Eastern Himalaya region of India and similar ecosystems.