The different effects of nitrogen-flow (NF) and air-limitation (AL) pyrolysis on the characteristics and nutrient retention of biochars (BCs) are unclear. Hence, in this study, BCs derived from bamboo, corn straw, and wheat straw were produced in AL and NF atmospheres at various temperatures (300-750 °C), and their different characteristics and nutrient retention rates were compared systematically. Nitrogen-flow pyrolysis facilitates C retention and graphitic C formation, and AL pyrolysis improves the polarity and supports the formation of oxygen-containing groups. With increasing pyrolysis temperature, C retention and graphitic C formation in BCs derived from AL pyrolysis decreases more significantly compared with BCs from NF pyrolysis. At 750 °C, the polarity and oxygen-containing groups of BCs derived from AL pyrolysis increase, whereas those from BCs derived from NF pyrolysis decrease. The observations are attributable to the AL and high-temperature-enhanced oxidization and gasification of C. An AL atmosphere with a higher pyrolysis temperature supports porosity and results in a larger specific surface area. Although pyrolysis temperature and atmosphere have negligible effects on nutrient retention, a low pyrolysis temperature facilitates the formation of water-soluble Ca, Mg, and P, and AL pyrolysis facilitates the formation of water-soluble P because the high pyrolysis temperature improves the pH and mineral stability of BCs, and air limitation facilitates the oxidation of organic P into PO4 3- . This study provides a reference for selecting AL or NF pyrolysis based on various pyrolysis temperatures to produce BCs and applying these in C sequestration, contaminant sorption, and soil quantity improvement.

中文翻译：

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氮流和限气气氛下产生的生物炭特性和养分保留的差异

氮气流 (NF) 和限气 (AL) 热解对生物炭 (BC) 特性和养分保留的不同影响尚不清楚。因此，在本研究中，在不同温度（300-750 °C）的 AL 和 NF 气氛中生产源自竹子、玉米秸秆和小麦秸秆的 BCs，并系统地比较了它们的不同特性和养分保留率。氮气流热解促进 C 保留和石墨 C 形成，AL 热解改善极性并支持含氧基团的形成。随着热解温度的升高，与来自 NF 热解的 BCs 相比，来自 AL 热解的 BCs 中的 C 保留和石墨 C 形成更显着降低。在 750 °C 时，AL 热解衍生的 BCs 的极性和含氧基团增加，而来自 NF 热解的 BCs 的那些减少。这些观察结果归因于 AL 和 C 的高温增强氧化和气化。具有较高热解温度的 AL 气氛支持孔隙率并导致更大的比表面积。虽然热解温度和气氛对养分保留的影响可以忽略不计，但低热解温度有利于水溶性 Ca、Mg 和 P 的形成，而 AL 热解有利于水溶性 P 的形成，因为高热解温度提高了 pH 值和BCs 的矿物稳定性和空气限制促进有机 P 氧化成 PO4 3- 。该研究为根据不同的热解温度选择AL或NF热解生产BCs并将其应用于C封存提供了参考，