Wheat straw biochar application increases ammonia volatilization from an urban compacted soil giving a short-term reduction in fertilizer nitrogen use efficiency

Purpose The potential for using biochar to reclaim degraded urban land into productive land needs to be verified to address the incipient loss of agricultural land. Materials and methods A pot experiment was conducted to evaluate the effect of wheat straw biochar (with four application rates including 0, 0.5%, 1%, and 2% w /w biochar to soil) on selected soil properties and crop growth (paddy rice was grown followed by wheat) in a compacted urban homestead soil (Anthrosol). Nitrogen use efficiency and ammonia volatilization were determined using stable isotope methodologies. Results and discussion Wheat straw biochar amendments elevated the soil pH, total C, and C/N ratio, and significantly lowered ( P < 0.05) the soil bulk density by 12.0–17.7% with doses of 1–2%. Increasing doses of biochar (1–2%) increased ammonia volatilization by 91.4–107.0% during the flooded rice season, which resulted in significantly lower ( P < 0.05) rice yield. This was reflected in the reduction of fertilizer 15 N use efficiency, which was 32.6–76.0% lower ( P < 0.05) than the control. However, the following wheat yield was significantly increased ( P < 0.05) by 23.0% with 2% biochar amendment, while there were no differences in ammonia volatilization between biochar amendments and the control. Conclusions Application of wheat straw biochar to a reclaimed urban Anthrosol increased seasonal flooded rice ammonia volatilization; however, no effect on ammonia volatilization was detected from the following aerobically grown wheat. The soils had a lower bulk density following biochar amendment and improved pH, which may have resulted in the higher wheat yield.