Rice straw biochar effects on Atterberg limits and aggregate characteristics of an Acrisol in Ghana

The stability and strength of soil aggregates to external forces such as raindrop impact and tillage may be affected by biochar application. In line with this, a three-year field experiment was conducted to investigate the effect of rice straw biochar (0, 15, and 30 t ha⁻¹) on the Atterberg limits (plastic limit, PL and liquid limit, LL), water-dispersible clay content (WDC), and the aggregate characteristics of an Acrisol. Aggregate characteristics were measured on four size classes (1–2, 2–4, 4–8, and 8–16 mm). The 30 t ha⁻¹ treatment significantly (p < 0.05) increased PL and LL by 27% and 20%, respectively, compared to the control. The plasticity index, WDC and tensile strength were unaffected by biochar addition. For all treatments, there was a decreasing trend in tensile strength with increasing aggregate size. The 15 and 30 t ha⁻¹ treatments increased friability by 21% and 38%, respectively, relative to the control. The 30 t ha⁻¹ treatment significantly increased workability of the smaller aggregates but marginally increased the workability of the larger aggregates. Thus, there is potential for increased optimum water content at tillage (inferred from the PL) and increased workability after biochar application at 30 t ha⁻¹.