The impacts of biochar application on soil hydrology, erosion and related properties.

Biochar production and application to soil can mitigate climate change and improve soil quality. This thesis investigated the influence of biochar preparation methods and application rates on the hydrological and erosional characteristics of biochars themselves and the soils to which they were applied. Biochar hydrophobicity was influenced by feedstock and decreased with increasing highest treatment temperature (HTT). Biochar did not influence soil wettability and the effect of HTT on biochar porosity was more important for soil water-holding capacity than its effect on hydrophobicity. HTT affected biochar yield, cation exchange-capacity and provision of fungal substrates. HTT also significantly influenced the effect of biochar on soil suction. Smaller feedstock particles produced biochars that were slightly more hydrophobic than those produced from larger particles. The effects of biochar application on the properties of sandy loam were influenced by biochar particle size, because larger particles had less effect on bulk density and had slower water uptake. A low biochar application rate (5 g kg-1) had no effect on the aggregate stability of a silt loam and did not affect the hydrological and erosional response of the soil under simulated rainfall. Application rates of 25 and 50 g kg-1 reduced aggregate stability, which led to surface sealing and overland flow generation occurring more readily. However, there was no more erosion of these soils than those with low or zero biochar content, and the crusts formed by seal drying were much weaker than those formed on soils with low or zero biochar. Biochar was preferentially eroded from the soils, regardless of the application rate used. HTT and particle size can have important implications both for the properties of biochar itself and for its effects on soil properties. However, biochar may only substantially influence soil hydrology and erosion when applied at sufficiently high rates