Evaluating effects of pyrogenic organic matter and biochar amendments on soil structure, soil chemical properties and soil fauna dynamics in tropical agroecosystems

During vegetation clearance to cultivated lands, charcoal making eliminates canopy effects on soil associated with trees while at the same time creating new conditions in and around such charcoal-making spots due to increased concentration of pyrogenic organic matter (PyOM). It is unclear how and/or whether such (un)intentional management practices affect the abundance, diversity and distribution patterns of soil macrofauna. However, biochar has been proposed as an amendment for improving soil fertility as well as a means of sequestering C into the soil. Nonetheless, biochar effects on soil macrofauna has received little attention despite the profound role they play in soil ecosystems. Therefore, the objectives of this work were to: i) assess effects of Croton megalocarpus and Zanthoxylum gilletii trees on the abundance, spatial distribution of soil macrofauna, and soil aggregation, ii) assess influence of converting these trees to PyOM on spatial distribution of soil macrofauna, iii) evaluate influence of PyOM from these trees on earthworm cast production in a mesocosm study, and iv) evaluate potential of biochar and fertiliser + biochar blends in restoring fertility of a nutrient deficient soil and the effects on soil fauna abundance and diversity. Biochar used in this study was prepared from Prosopis juliflora, a common invasive shrub found in the semi-arid parts of Kenya. In the field study, soil macrofauna samples were collected at increasing distances from the tree stems and the centre of charcoal-making spots. In the greenhouse study, earthworm casts were collected after every two days and at the end of experiment (at 30 days) as a measure of earthworm activity. In the on-station trial, soil and soil fauna samples were collected six and eight weeks after crop emergence.