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Supported by the National Science Foundation's Basic Research to Enable Agricultural Development (BREAD) program

Above: Pyrolysis cookstove, charcoal in the rhizosphere, and biochar impacts in a Kenyan smallholder plot. (photos: D. Torres, J. Lehmann, D. Guerena)

Project Description
Biochar-based inoculants and pyrolysis cookstoves for
human and soil health

Biofuels and biochar production for energy self-sufficiency and agricultural sustainability

This NSF-BREAD project combines soil science, engineering, and epidemiology to advance the health of smallholder farmers and the productivity of their farms. We are researching pyrolysis cookstoves as a way to reduce fuel gathering impacts and the harmful health effects of kitchen smoke, and the use of resulting biochar as an inoculant carrier and soil amendment to promote better crop growth and improve nutrient cycling. We will address the following broad research questions with a number of research activities:

  • Can we build an advanced pyrolysis cookstove with the lowest possible smoke emissions that reduces fuel use and produces appropriate biochar for use as an inoculant carrier?
    • Modeling of combustion and pyrolysis processes to design an efficient stove that can use crop residues, wood, and other biomass sources as fuel.
    • Testing emissions and use of the stoves compared to typical cooking practices in Kenyan rural households, to demonstrate potential health benefits from more widespread use of the stove.
    • Measurement of biochar production by the stoves and characterization of the char for potential use as an inoculant carrier and soil amendment.
  • Could biochar be a sustainable alternative to peat-based inoculants in improving crop productivity?
    • Testing characteristics of chars and mechanisms that lead to the best performance of chars as inoculant carriers, measured as storage characteristics, success in inoculation of crops, and persistence in soils.
    • Developing methods for local and lab-based production of inoculants using biochar.
    • Testing combinations of different inoculant organisms (mycorrhizae, rhizobia, other bacteria) with different chars and soils to identify the char and soil characteristics for maximal impact.
  • What impacts would improved cookstove fuel use and biochar in soils have on sustainabilty of household biomass fuel stocks and crop productivity?
    • Developing a model of household biomass energy use and potential impacts of increased stove efficiency of fuel use and additional fuel sources such as crop residues.
    • Testing impacts on crop productivity in soils of Western Kenya and other potential soils where inoculant strategies and biochar application might be considered, and comparing the impact of char used as an inoculant with char used alone.
    • Identification of mechanisms of biochar that change nutrient cycling from use as a microbial inoculants carrier, or via characteristics of char and impacts on nutrient cycling processes: nitrogen transformations and losses from soil, phosphorus availability, and movement of nutrients in watersheds.

Our research area in Western Kenya allows us to examine these questions along a gradient of soil degradation that ranges from newly-cultivated areas along a forest edge, to communities where soils and ecosystems have been depleted by 100 years of cultivation and fuel harvesting.

Funding for the project is provided by the Basic Research to Enable Agricultural Development (BREAD) program of the U.S. National Science Foundation.

Background and justification: soil degradation and household air quality risks in the developing world.

This research addresses two urgent problems in developing country contexts. The first of these is the loss of productivity of smallholder agro-ecosystems associated with fuelwood harvest as well as the degradation of soil carbon, beneficial microbial communities, and nutrient cycling in soils. The second is the negative human health impacts of existing uses of biomass fuels in rural households of developing countries.

Sub-Saharan Africa remains the area with the highest rate of food insecurity (Ahmed et al., 2007). Africa’s food insecurity is directly related to insufficient total food production (Sanchez, 2002), and the rapid increase in soil degradation is the primary threat to agricultural productivity in Africa (Lal, 2006). Soil degradation is set in motion primarily when forests and grasslands are cleared for agriculture (Solomon et al., 2007) and by the need to cultivate marginal lands to increase food production. Initially, farmers see an increase in agricultural productivity as native soil organic matter is mineralized and nutrients are released. However, constant cultivation, without returns of organic matter (e.g., crop residues) or nutrients to the soil, rapidly leads to reduced crop productivity (Kimetu et al., 2008; Ngoze et al., 2008). Reduced soil organic matter and plant productivity can lead to an impoverished soil microbial community in which beneficial plant-microbial symbioses such as those with mycorrhizae and beneficial bacteria in the root zone are impaired in their ability to promote crop growth. We hypothesize that biochar as a microbial inoculant carrier and soil amendment may produce beneficial shifts in microbial communities and nutrient cycling that will stabilize or reverse soil degradation processes.

Unsustainable agricultural practices are not the only causes of soil degradation. Rural households in most developing countries depend on biomass as a source of energy.  Most of it comes from woody biomass, either used as firewood or charcoal for cooking (Okello et al., 2001; Wamukonya, 1995). Although individual households may harvest wood from their own farmland or gather dead wood from protected lands, the main source of wood for charcoal making comes from the forest (Vajpeyi et al., 2001).  It is estimated that, in Africa, losses of 5 million ha of forest occur annually. In comparison to three-stone fires or traditional cookstoves, biochar producing pyrolysis cookstoves we will be developing could simultaneously provide a sustainable source of inoculant carrier material and also reduce pressure on woody biomass resources, by using a wider range of fuels from crop residues or other vegetation..

In addition to soil degradation there are serious adverse health effects from the use of biomass fuels in traditional cook stoves or ‘three stone fires’ from poor indoor air quality. About half of the world’s population, 3.2 billion people, still relies on coal and biomass fuels, such as wood, dung and crop residues to satisfy basic energy needs (Rehfuess et al., 2006). Indoor air pollution from burning these solid fuels on open fires or in traditional stoves is responsible for 1.5 million deaths every year (World Health Organization, 2006). Women and children are the most affected, since they spend the most time in the kitchen. In fact, indoor air pollution from inefficient household stoves has been causally linked to acute lower respiratory infections (Smith et al., 2008), the leading cause of mortality globally in children under 5 years of age. We expect that a next-generation clean burning pyrolysis cookstove can reduce smoke and other pollutant emissions to levels that would provide dramatic impacts on maternal-child health.

References and Reading:
Ahmed A, Vargas Hill R, Smith LC, Wiesmann DM, Frankenberger T 2007. The world’s most deprived: Characteristics and causes of extreme hunger. 2020 Discussion Paper No. 43, International Food Policy Research Institute, Washington D.C.

Kimetu J, Lehmann J, Ngoze S, Mugendi D, Kinyangi J, Riha S, Verchot L, Recha J, Pell A 2008. Reversibility of soil productivity decline with organic matter of differing quality along a degradation gradient. Ecosystems 11: 726-739.

Lal R 2006. Enhancing crop yields in the developing countries through restoration of the soil organic carbon pool in agricultural lands. Land Degradation and Development 17: 197–209.

Lehmann, .J, Gaunt, J. and Rondon, M.: 2006, 'Bio-char sequestration in terrestrial ecosystems – a review', Mitigation and Adaptation Strategies for Global Change 11, 403-427.

Lehmann, J.: 2007, 'A handful of carbon', Nature 447, 143-144.

Marris, E.: 2006, 'Black is the new green', Nature 442: 624-626.

Ngoze S, Riha S, Lehmann J, Kinyangi J, Verchot L, Mbugua D, Pell A 2008. Nutrient constraints to tropical agroecosystem productivity in long-term degrading soils. Global Change Biology 14: 2810-2822.

Okello BD, O’Connor TG, Young TP 2001. Growth, biomass estimates and charcoal production of Acacia drepanolobium in Laikipia, Kenya. Forest Ecology and Management 142:143-153.

Rehfuess E, Mehta S, Prüss-Üstün A 2006. Assessing household solid fuel use- multiple implications for the Millennium Development Goals. Environmental Health Respect 114: 373-8.

Sanchez PA 2002. Ecology - Soil fertility and hunger in Africa. Science 295: 2019- 2020.

Smith KR 2008. Wood, the Fuel that Warms You Thrice. pp 97-111. In Colfer CJP (ed.), Human Health and Forests: A Global Overview of Issues, Practice, and Policy. Earthscan, London.

Solomon D, Lehmann J, Kinyangi J, Amelung W, Lobe I, Ngoze S, Riha S, Pell A, Verchot L, Mbugua D, Skjemstad J, Schäfer T 2007a. Long-term impacts of anthropogenic perturbations on the dynamics and molecular speciation of organic carbon in tropical forest and subtropical grassland ecosystems. Global Change Biology 13: 511-530.

Vajpeyi DK 2001. Deforestation in the Democratic Republic of Congo and Kenya. In Vajpeyi DK (ed.) Deforestation, Environment and Sustainable Development: A Comparative Analysis. Praeger, Westport, CT.

Wamukonya L 1995. Energy consumption in three rural Kenyan households: A survey. Biomass and Bioenergy 8(6): 445-451.

WHO (World Health Organization) 2006. Indoor Air Pollution: 4000 deaths a day must not longer be ignored. Bulletin of the World Health Organization; July 2006, 84 (7).

Yaman, S.: 2004, 'Pyrolysis of biomass to produce fuels and chemical feedstocks', Energy Conversion and Management 45, 651-671.