Continuous application of phosphorus (P) nutrient in association with its low recovery results in large amounts of P being accumulated in soil in different forms. Use of biochar can be a possible means to mobilize soil legacy P and increase its bioavailability. Therefore, the aim of this study was to identify the potential impact of a range of biochar types on P fractions in a long-term cultivated arid soil with high legacy P content. The soil was treated with biochar produced from four feedstock sources (BFS): sewage sludge (SSB), olive mill pomace (OPB), chicken manure (CMB), and date palm residues (DRB) pyrolyzed at 300, 500, or 700 °C in addition to an untreated control. The soil biochar mixture was incubated for 1 month followed by soil P fractionations using sequential chemical extraction to separate soil P into: labile (Resin-Pi, NaHCO3-Pi, NaHCO3-Po), moderately labile (NaOH-Pi, NaOH-Po), and non-labile (HCl-Pi and Residual-P) pools. Biochar addition clearly influenced most of the soil P fractions; however, the extent of this effect greatly varied depending on BFS and pyrolysis temperature (PT). The most evident biochar impact was observed with labile P pool, with the greatest increase being observed in NaHCO3-Pi fraction in most biochar treatments. Irrespective of PT, SSB and CMB were the most effective biochar type in increasing labile inorganic P; the SSB and CMB increased Resin-Pi by 77 and 206% and NaHCO3-Pi by 200 and 188%, respectively. In contrast, DRB made no changes in any P fraction. Differences in effects of biochar types on labile P is presumably related to the higher content of P in biowaste-based biochar compared to plant-based biochar which have much lower P content. The SSB, CMB, and OPB produced at low temperature reduced HCl-Pi content, indicating that these biochars may have stimulated organic matter decomposition and thereby dissolution of non-labile Ca-associated P to labile P forms. Overall, biochar addition appeared to be an effective approach in enhancing legacy P availability in arid soil. However, further studies are necessary to verify these findings in the presence of plant and for a longer period.

中文翻译：

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添加生物炭对长期耕作干旱土壤遗留磷有效性的影响

持续施用磷 (P) 养分及其低回收率导致大量 P 以不同形式在土壤中积累。使用生物炭可能是调动土壤遗留磷并提高其生物有效性的一种可能手段。因此，本研究的目的是确定一系列生物炭类型对具有高遗留 P 含量的长期耕作干旱土壤中 P 组分的潜在影响。用四种原料来源 (BFS) 生产的生物炭处理土壤：污水污泥 (SSB)、橄榄磨渣 (OPB)、鸡粪 (CMB) 和在 300、500 或 700° 下热解的椰枣残渣 (DRB) C 除了未经处理的对照。将土壤生物炭混合物培养 1 个月，然后使用连续化学提取将土壤 P 分离成：不稳定的（树脂-Pi、NaHCO3-Pi、NaHCO3-Po)、中度不稳定（NaOH-Pi、NaOH-Po）和不稳定（HCl-Pi 和残留-P）池。生物炭的添加明显影响了大部分土壤磷含量；然而，这种影响的程度取决于 BFS 和热解温度 (PT)。在不稳定的 P 池中观察到最明显的生物炭影响，在大多数生物炭处理中观察到的 NaHCO3-Pi 分数增加最大。不考虑 PT，SSB 和 CMB 是增加不稳定无机 P 最有效的生物炭类型；SSB 和 CMB 分别使 Resin-Pi 增加了 77% 和 206%，NaHCO3-Pi 增加了 200% 和 188%。相比之下，DRB 没有改变任何 P 分数。与 P 含量低得多的植物基生物炭相比，生物炭类型对不稳定 P 影响的差异可能与基于生物废物的生物炭中 P 含量较高有关。低温下产生的 SSB、CMB 和 OPB 降低了 HCl-Pi 含量，表明这些生物炭可能刺激了有机物分解，从而将不稳定的 Ca 相关 P 溶解成不稳定的 P 形式。总体而言，添加生物炭似乎是提高干旱土壤中遗留 P 可用性的有效方法。然而，需要进一步的研究来验证这些发现在植物存在的情况下和更长的时间。