Abstract:
Soil structure is a key soil physical property that affects soil water balance, gas transport, plant growth and
development, and ultimately plant yield. Biochar has received global recognition as a soil amendment with the
potential to ameliorate the structure of degraded soils. We investigated how corn cob biochar contributed to
changes in soil water retention, air flow by convection and diffusion, and derived soil structure indices in a
tropical sandy loam. Intact soil cores were taken from a field experiment that had plots without biochar (CT),
and plots each with 10 t ha-1 (BC-10), 20 t ha-1 without or with phosphate fertilizer (BC-20 and BC-20+P
respectively). Soil water retention was measured within a pF range of 1 to 6.8. Gas transport parameters (air
permeability, ka, and relative gas diffusivity, Dp/D0) were measured between pF 1.5 and 3.0. Application of
20 t ha-1 led to significant increase in soil water retention compared to the CT and BC-10 as a result of increased
microporosity (pores < 3 μm) whereas for soil specific surface area, biochar had minimal impact. No significant
influence of biochar was observed for ka and Dp/D0 for the BC treatments compared to the CT despite the larger
values for the two properties in the 20 t ha-1 treatments. Although not significant, the diffusion percolation
threshold reduced by 34% and 18% in the BC-20 and BC-20+P treatments, respectively, compared to the CT.
Similarly, biochar application reduced the convection percolation threshold by 15 to 85% in the BC-amended
soils. The moderate impact of corn cob biochar on soil water retention, and minimal improvements in convective
and diffusive gas transport provides an avenue for an environmentally friendly disposal of crop residues, particularly for corn cobs, and structural improvement in tropical sandy loams
