**Yu-Lin Kuo 1, Chia-Hisng Lee <sup>2</sup> and Shih-Hao Jien 3,\***


Received: 4 June 2020; Accepted: 13 July 2020; Published: 15 July 2020

**Abstract:** *Background*: Loss of nutrients and organic carbon (OC) through leaching or erosion may degrade soil and water quality, which in turn could lead to food insecurity. Adding biochar to soil can effectively improve soil stability, therefore, evaluating the effects of biochar on OC and nutrient retention and leaching is critical. *Methods*: We conducted a 42-day column leaching experiment by using sandy loam soil samples mixed with 2% of biochar pyrolyzed from Honduran mahogany (*Swietenia macrophylla*) wood sawdust at 300 ◦C (WB300) and 600 ◦C (WB600) and a control sample. Leaching was achieved by flushing the soil column on day 4 and every week during the 42-day experiment and adding a water volume for each flushing equivalent to the field water capacity. *Results*: Biochar application increased the final soil pH and OC, NH4 <sup>+</sup>-N, NO3 −-N, available P concentrations but not exchangeable K concentrations. In particular, WB600 exhibited superior performance in alleviating soil acidification; WB300 engendered high NO3 −-N concentrations. Biochar application effectively retained water in soil and inhibited the leaching of the aforementioned nutrients and dissolved OC. WB300 reduced NH4 <sup>+</sup>-N and K leaching by 30%, and WB600 reduced P leaching by 68%. *Conclusions*: Biochar application can improve nutrient retention and reduce the leaching potential of soils and connected water bodies.

**Keywords:** biochar; organic carbon; nutrients; leaching; nitrogen; phosphorus; potassium
