Sewage sludge-derived biochar (SSBC) could improve nitrogen (N) use efficiency (NUE) and reduce the use of mineral N fertilizers in agriculture. However, information on the residual effect (after stopping amendment) of SSBC on NUE is scarce, but necessary, to evaluate how often biochar should be applied to agricultural crops. In this study, the residual effect of SSBC produced at different temperatures on NUE of corn, by using the ¹⁵N isotope tracer, was investigated. The following treatments were assessed in a tropical field study carried out for four years: (a) MF—mineral fertilizer application with nitrogen, phosphorus and potassium (NPK); (b) MF + SSBC produced at 300°C (B3 + MF); and (c) MF + SSBC produced at 500°C (B5 + MF). The contents of soil total N (TN), N in corn derived from the soil (NDS) and from mineral fertilizer (NDMF) were determined. In addition, the N-fertilizer recovery efficiency (NFRE) in the corn grains and straw was evaluated. Application of SSBC increased N uptake by corn from both the fertilizer (NDMF) and the soil (NDS). All treatments presented similar grain yields. On average, the plants took up N predominantly from soil (88.5 kg ha^‒1 in straw; 68.7 kg ha^‒1 in grains) compared with mineral fertilizer (51.9 kg ha^‒1 in straw; 62.3 kg ha^‒1 in grains). Results of the current study indicate that SSBC is able to improve the N use efficiency, even two years after amendment, and consequently, it may reduce the use of mineral fertilizers in agriculture.

中文翻译：

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污水污泥生物炭提高氮肥回收率：来自 15N 示踪剂现场研究的证据

污水污泥衍生生物炭 (SSBC) 可以提高氮 (N) 的利用效率 (NUE)，并减少农业中矿物氮肥的使用。然而，关于 SSBC 对 NUE 的残余影响（停止修正后）的信息很少，但对于评估生物炭应用于农作物的频率是必要的。本研究利用¹⁵种不同温度下 SSBC 对玉米 NUE 的残留影响研究了 N 同位素示踪剂。在一项为期四年的热带田间研究中评估了以下处理： (a) MF——施用含氮、磷和钾 (NPK) 的矿物肥料；(b) MF + SSBC 在 300°C 下生产 (B3 + MF)；(c) MF + SSBC 在 500°C 下生产（B5 + MF）。测定了土壤全氮（TN）、土壤（NDS）和矿物肥料（NDMF）中玉米中的氮含量。此外，还评估了玉米粒和秸秆中的氮肥回收效率 (NFRE)。SSBC 的施用增加了玉米从肥料 (NDMF) 和土壤 (NDS) 中吸收的氮。所有处理都表现出相似的谷物产量。平均而言，植物主要从土壤中吸收氮（88.5 kg ha ^‒1秸秆；68.7 kg ha ^‒1谷物）与矿物肥料（稻草51.9 kg ha ^‒1；谷物62.3 kg ha ^‒1）相比。目前的研究结果表明，SSBC 能够提高氮的利用效率，即使在修改后两年，也可以减少农业中矿物肥料的使用。