Archive for the ‘soil science’ Category

Quantifying biochar impact on soil

December 3, 2010

Discussions with IRRI gave some simple assumptions which can be used when assessing the impact of biochar addition on the soil.

If biochar analysis is available, then the impact of a known volume of biochar to soil can be calculated. For example, if one square metre of soil is amended with 4 kg of biochar (this is a 40 t/ha application rate), then we can assume that this represents 4% of the soil weight. This is because in 1 m at a 10 cm depth there is 100 litres of soil with an approximate bulk density of 1, which is 100 kg of soil. The properties of the biochar can then be assumed to be diluted in the soil at a 4% rate.

This assumption was then applied to the CEC (Cation Exchange Capacity) where rice husk biochar is added to the research farm soil in Siem Reap, Cambodia.
The soil has a CEC of 18.44 cmol+/kg
Biochar has a CEC of 44.5 cmol+/kg.

Therefore the CEC of the soil can be assumed to be raised to (18.44*0.96)+(44.51*0.04) = 19.48

This is a rough assumption, and should not substitute using actual data, and it assumes that there are no interactions between the soil and the biochar which could influence the CEC of the soil.

Biochar application physically alters soil

June 17, 2010

The third cycle of crops grown in the pot trials at the Apsara farm were harvested today. The lettuce were grown for 28 days in the pots, after a 14 day germination period in growing treys.

Biochar is reported to improve soil structure, as it can alter porosity, particle size, infiltration, drainage and water storage capacity. The physical impact of biochar in the pot trial soil was easily identifiable; it was much easier to remove the plant from the pot and the soil from the roots of the lettuce. A dense structure like that of the unammended pot will reduce the ability of the air and water to move through the soil and will make it more difficult for the plant roots to propagate through the soil.

The pictures show the two of the amendments, the soil clods are visible in the left hand picture (T0) which does not have any amendments. The picture in the right shows the biochar (84t/ha equivalent addition), compost and sediment amended soil.

Un-amended soil after lettuce harvest in pot trials. 17.06.2010

Biochar amended soil after lettuce harvest in pot trials. 17.06.2010