07. Expected benefits from biochar

In this project, to assess the benefit, we will measure yield of the crop and in some cases leaf number, plant height and root mass. We will also test soil, both in and ex-situ to identify physical and chemical benefits to the soil.

However we can predict in advance some of the benefits which biochar might bring to an agricultural system in Cambodia. These are:

Soil structure / physical properties: Water retention, infiltration rate, reduced soil albedo (reflectance of the soil). Chan et al (2007) observed improvements to hardsetting soil including reduction in tensile strength and increases in field capacity when >50t/ha biochar was added.

Soil nutrient balance: Available levels of minerals in the rice husk biochar samples from Cambodia are in some cases significant. They provide up to 90.8 c+mol/kg of exchangeable K, 21.0 c+mol/kg of exchangeable Na, 14.9 c+mol/kg of exchangeable Ca and 12.8 c+mol/kg of exchangeable Mg. Trace minerals have been detected in the samples and results are available for mg/kg dry weight for 22 different metals.
The priming effect (the accelerated decomposition of organic material in the soil) may be a negative effect however this is a very highly debated topic.

Other plant – soil interactions:
Rondon et al (2007) showed that the addition of biochar led to an increased proportion of fixed nitrogen. Three related mechanisms were identified which lead to this:
– there could be more mychorrizal activity inside the biochar, which can bring more nutrients to plant roots which seek out biochar in the soil
– the N ratios is lower in the soil due to low C:N in biochar (the C:N ratio is 44:1 in the biochar used for field trials).
– increased availability of micro nutrients and higher pH (this is 7.79 for the biochar)

Chemical effects: A high pH biochar will have a liming effect. The high CEC of biochar may increase the retention of available nutrients in the soil (available N as NH4+). In literature many benefits to crop yield are most prominent when the addition of biochar is in combination with N fertiliser addition, potentially due to the presence of biochar reducing the availability of N.

Fixed carbon: the non-labile carbon which is unavailable to plants is stable so may be used to redeem carbon credits. This finance can indirectly benefit agriculture.

Leaching of added chemicals / bioremediation: biochar may reduce leaching of excess agrichemicals added farms. Chan et al (2007) showed that biochar addition with fertiliser increased radish production, although biochar amendment alone did not increase the yield of radish. Changes in soil quality were also noted A related effect is also identified in Asai et al, where the addition of biochar is

These benefits over time will change, as the labile carbon fraction is lost, and particle size decreases and potentially CEC increases.

References:

Hidetoshi Asai, Benjamin K. Samson, Haefele M. Stephan, Khamdok Songyikhangs, Koki Homma, Yoshiyuki Kiyono, Yoshio Inoue, Tatsuhiko Shiraiwa, Takeshi Horie. Biochar amendment techniques for upland rice production in Northern Laos. 1. Soil physical properties, leaf SPAD and grain yield. Field Crops Research 111 (2009) 81–84

K. Y. Chan, L. Van Zwieten, I. Meszaros, A, Downie. C, and S. Joseph
Australian Journal of Soil Research, 2007, 45, 629–634. Agronomic values of greenwaste biochar as a soil amendment

Rondon, M.A., Lehmann, J., Ramirez, J. and Hurtado M. (2007) Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions. Biol Fertil Soils (2007) 43:699-708.

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