Biochar: Effects on Soil and Crops

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Soil fertility and quality

Organic matter added to soil helps it retain nutrients that are essential to plant growth. Proponents of biochar say that it is much more effective than other organic matter in retaining nutrients and keeping them available to plants. A study by Johannes Lehmann says this is also true for phosphorus, which is not retained by 'normal' soil organic matter.[1]

Researchers who have tested the impact of charcoal on soil fertility say that much of the benefit may derive from charcoal’s vast surface area and complex pore structure, which is hospitable to the bacteria and fungi that plants need to absorb nutrients from the soil. Christoph Steiner, a research scientist at the University of Georgia, says, "We believe that the structure of charcoal provides a secure habitat for microbiota, which is very important for crop production." Steiner and coauthors noted in their 2003 book Amazonian Dark Earths that the charcoal addition to soil caused a 280-400% increase in plant uptake of nitrogen.[2]

A report for Biofuelwatch, however, says that over-reliance on biochar to create soil fertility is dangerously reductionist. It says the farmers who created terra preta added different types of biomass the soil, thus building up humus as well as charcoal. Biochar advocates, on the other hand, “promote stripping the land of ‘agricultural and forestry residues’, which would greatly reduce humus.” Done on a large scale, the report warns, this would “replace at least some humus with biologically dead charcoal, an untested but potentially very dangerous strategy.”[3]

Water retention of soil

A survey of published studies showed that only sandy soils had higher available moisture after charcoal additions. Clay soils (which are naturally good at retaining water) showed decreased moisture content with increasing charcoal additions.[4]

Crop yield

According to Cornell University Department of Soil and Crop Sciences, “Soils with biochar additions are typically more fertile [and] produce more and better crops for a longer period of time.”[5]

This is largely confirmed by studies examining the effects on crop yield of added charcoal. Most show positive results in the short term, though in a few cases, either no difference or negative results have been found. Longer-term studies are lacking.

Here are the results of studies on the impact on yield of adding charcoal to soil:

  • Research on peas and mung beans in India showed an 160% and 122% biomass increase respectively[6]
  • Research in Japan on soybeans grown on volcanic ash loam showed an 151% biomass increase at an application rate of 0.5 Mgha-1 (megagrams per hectare, a megagram being a metric ton). However, higher rates of application decreased yield: 5 Mgha-1 of char decreased yield to 63% and 15 Mgha-1 char decreased yield to 29%[7]
  • Research in Japan on sugi trees (the national tree of Japan, often grown near temples) on clay loam with addition of charcoal from different sources at an application rate of 0.5 Mgha-1 found:[8]
wood charcoal increased biomass 249%
bark charcoal increased biomass 324%
activated charcoal increased biomass 244%
  • Research on bauhinia trees found increased biomass by 13% and height by 24%[9]
  • Research on cowpeas found 150% biomass increase from application rates of 67 Mgha-1 and 200% biomass increase from application rates of 135 Mgha-1[10]
  • Research on cowpeas and rice at the Embrapa Amazonia Ocidental, Manaus, Brazil found a 38-45% increase in biomass (no yield reported)[11]
  • Research in Ghana on maize grown on disused charcoal production sites and adjacent fields found a grain yield 91% higher and biomass yield 44% higher on the charcoal site than the control[12]
  • Research on maize, cowpea and peanuts on low fertility soil found acacia bark charcoal plus fertilizer increased maize and peanut yields (but not cowpea)[13]
  • Research on radishes on heavy soil using commercial greenwaste biochar at three different rates of application showed increased yield only in combination with nitrogen fertilizer[14]
  • Research on common beans in Colombia found increased nitrogen fixation through charcoal additions, resulting in increased bean yield by 46% and biomass production by 39%
  • Research over four cropping cycles with rice and sorghum found that charcoal amended with chicken manure resulted in the highest cumulative crop yield
  • Research on maize on degraded soil in Kenya showed that charcoal doubled crop yield.

Resources

Notes

  1. ↑ Lehmann, J., 2007 Bio-energy in the black. Frontiers in Ecology and the Environment 5, 381-387.
  2. ↑ Tenenbaum, David J., Biochar: carbon mitigation from the ground up, Environmental Health Perspectives, Feb 2009 v117 i2 pA70–74.
  3. ↑ Almuth Ernsting and Rachel Smolker, “Biochar for Climate Change Mitigation: Fact or Fiction?”, Biofuelwatch, February 2009, p. 4
  4. ↑ Glaser B, Lehmann J, Zech W (2002) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal—a review. Biol Fertil Soils 35:219–230
  5. ↑ “Biochar: The new frontier,” Cornell University Department of Soil and Crop Sciences, Cornell University website
  6. ↑ Iswaran V, Jaiuhri KS, Sen A (1980), “Effect of charcoal, coal and peat on the yield of moong, soybean and pea”, Soil Biol Biochem 12:191–192
  7. ↑ Kishimoto S, Sugiura G (1985), “Charcoal as a soil conditioner”, Int. Achieve Future 5:12–23
  8. ↑ Kishimoto S, Sugiura G (1985), “Charcoal as a soil conditioner”, Int. Achieve Future 5:12–23
  9. ↑ Chidumayo E.N. (1994), “Effects of wood carbonization on soil and initial development of seedlings in miombo woodland, Zambia,” Forest Ecological Management 70: 353–357
  10. ↑ Glaser, B., Lehmann, J., Zech, W., 2002. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal – a review. Biology and Fertility of Soils 35, 219-230.
  11. ↑ Lehmann, J., da Silva Jr, J.P., Steiner, C., Nehls, T., Zech, W., Glaser, B., 2003. Nutrient availability and leaching in an archaeological Anthrosol and a Ferralsol of the Central Amazon basin: fertilizer, manure and charcoal amendments. Plant & Soil 249, 343-357.
  12. ↑ Oguntunde, P.G., Abiodun, B.J., Ajayi, A.E., van de Giesen, N., 2008. Effects of charcoal production on soil physical properties in Ghana. Journal of Plant Nutrition and Soil Science 171, 591-596.
  13. ↑ Yamato, M., Okimori, Y., Wibowo, I.F., Anshori, S., Ogawa, M., 2006. Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Science and Plant Nutrition 52, 489 - 495.
  14. ↑ Chan, K.Y., Van Zwieten, L., Meszaros, I., Downie, A., Joseph, S., 2007. Agronomic values of greenwaste biochar as a soil amendment. Australian Journal of Soil Research 45, 629-634.
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