For comparison, a further analysis by McHenry (2012a, b) was undertaken of the value of applying bio­char at 1 t/ha with the full rate of SSP as described above. This analysis was undertaken to explore the rela­tive impact of using biochar to increase yield, as opposed to increasing fertilizer use efficiency. The anal­ysis assumed that using the full rate of SSP (90 kg/ha year) with a 1 t/ha year application of biochar increased wheat yields by 15% on average over the 15 years rela­tive to full SSP applications only, in the southwest of WA2. The baseline yield used for the scenario was 1.75 t/ha, an approximate average wheat yield for WA. The assumptions of the model, including a total area wheat return increase of $71.75/ha, were based on an increased production of an additional 15% wheat yield from the 1.75 t/ha at a constant value of $350/t over

the 15 years using the 8% real discount rate. The scenario did not include additional harvesting or transport costs for the additional wheat yield. The results indicated that the required carbon prices to recoup biochar purchase price costs were lower when biochar is used to increase yield, rather than reduce fertilizer use. When biochar purchase prices were below $250/t, the application of biochar was attractive without any carbon price, assuming the 15% yield is achieved (McHenry, 2012a). Therefore, these relatively simple analyses suggest that the most cost-effective on-farm use for biochar is to simply increase the wheat yield. The results confirm pre­vious assertions that agricultural biomass production for the sole purpose of producing biochar for soil carbon sequestration may not be economically feasible (Lehmann et al., 2006).