| Summary: | Biochar is a carbon rich material obtained by the incomplete combustion of biomass. Agronomically, biochar is used as a soil amendment, usually in combination with other amendments such as fertilizer or compost. For environmental purposes, biochar serves as a means of sequesting carbon, thus mitigating climate change. It also has remediating properties such as adsorbing contaminants from water and soils. In this study, different rates of rice straw biochar combined with various inorganic fertilizer rates were applied on rice fields. The field experiment was conducted in both the major season and minor season of the year 2018. The minor season cultivation had two fields: minor season main and minor season residual. The minor season residual field did not have biochar reapplied to it because it was to assess the residual effect of the biochar applied during the major season. The economic costs were computed from the cost involved in the activities of the rice production processes. Rice yield was harvested at maturity and the yield converted into revenue using prevailing selling price. Net Present Values (NPVs) and Benefit Cost Ratios (BCRs) were computed for each treatment. The results indicated that the use of biochar as soil amendment in rice production is costly during the first production cycle, however, its residual effect is able to yield benefits that outweigh the costs, thus making biochar usage profitable in the second cropping season. Generally, the major season (first cropping cycle) had low BCRs, ranging from 0.54 to 1.33 compared with those of the minor season residual fields (second cropping cycle), which were between 1.22 and 1.84. The minor season residual fields had NPVs that were generally higher (−724 to 2069) than those of the major season (−2757 to 1300).
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