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 ¹⁵N 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. [ABSTRACT FROM AUTHOR]