The effects of biochar on soil water properties can improve crop resilience to water-related stresses, such as drought and flooding, which are becoming increasingly frequent as a result of climate change.
How does it work?
Sponge-like Properties
Biochar is highly porous on multiple scales. This structure enables it to act as a sponge and improve soil water retention.
Improves Root Structure
Biochar can increase root biomass and improve crop root structure. Healthier root systems mean the plant is more effective at accessing available water in the soil. This improves the resilience of crops, especially in drought conditions. Root-zone application can improve local soil water properties, even with low-dose biochar applications.
High Porosity
The porous structure of biochar can benefit hydraulic conductivity (how easily water moves through pores in the soil), helping crops uptake water.
This is especially when applied to clay soils, which have poor hydraulic conductivity. In sandy soils, biochar decreases hydraulic conductivity which improves water retention. Both these effects improve plant available water.
Biochar in different soil types
Clay soils: Biochar improves water flow and reduces wilting point in clay soils.
Sandy soils: Biochar improves field capacity and water retention in sandy soils.
Dense soils: High dose biochar application lowers soil bulk density, increasing field capacity.
💡Using biochar effectively
The targeted application of tailored biochar to soils can increase the effectiveness of biochar on crop water accessibility and drought resilience. This is dependent on soil type. To achieve effects on soil water availability, large amounts of biochar (>10 tha−1) would have to be applied. Low-dose biochar application (<1t ha-1) at the root zone provides locally increased available water to the roots during the early stages of plant growth, when crops are especially vulnerable to drought.
- In sandy soils, small biochar particle size biochar with high specific surface area and porosity are more effective.
- In clayey soils, biochars with larger particle sizes and with high specific surface area are recommended.
- To improve bulk soil water properties, biochar application must achieve rates >10 t biochar ha-1.
- Low-dose targeted biochar application (<1 t biochar ha-1) without soil cultivation can improve plant available soil water if applied to the crop root zone.
