Biochar type and application methods affected nitrogen and phosphorus leaching from a sandy soil amended with inorganic fertilizers and biosolids

Abstract

Land application of biochar as a soil amendment can be an effective strategy for reducing nutrient leaching while providing simultaneous benefits to soil health. However, biochar effects on soil nitrogen (N) and phosphorus (P) dynamics in biochar-amended soils are poorly understood, particularly in Florida sandy soils receiving fertilizers. This study evaluated the effects of different biochar materials (particle size of 0.1 mm produced from pine (Pinus spp.) wood vs. ∼0.5–2 mm produced from fescue (Festuca arundinaceaSchreb.) grass, herein referred as “powder” and “coarse” biochar, respectively) and their application methods (surface vs. incorporated) on N and P leaching from soils amended with inorganic fertilizer or biosolids. Biochar materials were either mixed throughout columns of soil or surface applied at a 1% (w/w) rate. Columns were periodically leached over 6 mo to attain 138 ml (equivalent to ∼1 pore volume) of drainage in each event (total of ∼16 pore volume of leachate). Biochar materials exhibited modest affinity to retain ammonium (NH4+) but showed no ability to sorb nitrate (NO3–). Powder biochar incorporated throughout the soil reduced cumulative NH4–N, NO3–N, and total N mass leached (average of 25% reduction) relative to control (no biochar) treatments. Biochar materials acted as P sources and were ineffective in reducing leachate P. Biosolids generally resulted in significant lower risk of N and P leaching than inorganic fertilizer. Results suggested biochar ability to retain N and P in soils varies with biochar source, application method, and nutrient source. Biochar type and application method affected N and P dynamics in biosolids or inorganic fertilizer-amended soils, but understanding the mechanisms requires additional study.