Value of Functionalized Charcoal for Increasing the Efficiency of Urea N Uptake: Insights into the Functionalization Process and the Physicochemical Characteristics of Charcoal

ABSTRACT Functionalized charcoal (CHox) incorporated into urea is known for its ability to reduce NH3 volatilization and increase agronomic efficiency. However, it is important to optimize the functionalization process and to elucidate its relationship with the physicochemical properties of CHox for N supply. Thus, charcoal obtained from eucalyptus wood was functionalized with different HNO3 concentrations and reaction times. Ammonia adsorption by CHox was evaluated in chambers with high NH3 concentrations. Dry matter yield, N uptake, and apparent N recovery efficiency of corn plants were evaluated after the application of the urea-CHox mixture to soil in a greenhouse experiment. The properties of CHox, such as pH, isoelectric point, and total acidity (carboxylic and phenolics groups) depended on the HNO3 concentration but were not influenced by the reaction time. The NH3 adsorption by the functionalized charcoal showed a positive correlation with the quantity of carboxylic and phenolic groups and a negative correlation with the pH value and the isoelectric point. The small differences observed in dry matter yield, N accumulation, and apparent N recovery efficiency among the corn plants from urea mixed with CHox or humic acids derived from charcoal (AHCH) are not sufficient to determine the higher efficiency of these sources.摘要 已有研究证实，掺入尿素的官能化炭（CHox, functionalized charcoal）可降低氨（NH3）挥发量并提升农艺效率。然而，优化其官能化工艺并阐明其与CHox供氮相关理化性质之间的内在联系，仍具有重要研究意义。为此，本研究以桉木制备的炭材料为原料，采用不同浓度硝酸（HNO3）与反应时长对其进行官能化改性。通过高氨浓度培养箱体系，评估了CHox的氨吸附性能。通过温室土培试验，将尿素-CHox混合物施入土壤后，测定了玉米植株的干物质产量、氮吸收量与表观氮回收效率。CHox的理化性质，如pH值、等电点及总酸度（羧基与酚羟基基团含量），仅受硝酸浓度调控，而与反应时长无显著关联。官能化炭的氨吸附量与羧基、酚羟基基团的数量呈显著正相关，与pH值及等电点呈显著负相关。相较于添加炭源腐殖酸（AHCH, humic acids derived from charcoal）的尿素处理组，掺混CHox的尿素处理组在玉米干物质产量、氮积累量与表观氮回收效率上仅存在小幅差异，不足以证明此类氮源具备更优的施用效果。