Abstract Treating soil with a combination of nitrogen (N) and biochar (BC) has often been suggested as an approach to enhancing soil quality. In the present study, we therefore conducted a two -year randomized two-factorial field experiment in order to explore optimal N fertilizer management strategies in the context of BC application to calcareous soil, with a focus on both microbial activities and soil nutrient levels. Maize straw BC (0 or 22.5 t ha−1) was applied to the soil once prior to the planting of wheat, with four different N fertilizer concentrations (0, 150, 225, and 300 kg ha−1) being applied to experimental plots. We found that N fertilizer addition resulted in significant reductions in soil pH and available phosphorus (AP) levels, whereas soil phosphatase activity was increased by such treatment. Relative to treatment with only BC or N in isolation, the combined application of both N and BC led to significant increases in soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and available potassium (AK) levels, while also enhancing the activity of C- and N-cycling enzymes. In contrast, this combination treatment did not impact soil pH or phosphatase activity. The application of BC did not significantly affect microbial biomass, but it was associated with changes in overall microbial community structure, including a decrease in the fungi/bacteria ratio and the Gram-negative/Gram-positive bacteria ratio. These changes were also linked to increases in relative actinomycetes abundance and an elevated cy19:0/18:1ω7c ratio. These results suggested that combined N and BC application is thus not conducive to rapid fungal growth, with soil AK, pH, TN, and TDN being the primary factors that affected soil microbial community structure. While BC did significantly increase the βG:(NAG LAM) ratio, this was not associated with any N-mediated microbial restriction. Overall, our findings conclusively demonstrate that combined BC and N fertilizer application can enhance soil quality while supporting a more stable microbial community structure and more active soil biological activity.

中文翻译：

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在为期 2 年的田间试验中，生物炭和氮肥结合改变土壤酶和微生物活性

摘要 用氮 (N) 和生物炭 (BC) 的组合处理土壤经常被建议作为提高土壤质量的方法。因此，在本研究中，我们进行了为期两年的随机双因素田间试验，以探索在 BC 应用于钙质土壤的背景下的最佳氮肥管理策略，重点是微生物活动和土壤养分水平。在种植小麦之前，将玉米秸秆 BC（0 或 22.5 t ha-1）施入土壤一次，将四种不同浓度的氮肥（0、150、225 和 300 kg ha-1）施用于试验田. 我们发现添加氮肥导致土壤 pH 值和有效磷 (AP) 水平显着降低，而这种处理增加了土壤磷酸酶活性。相对于单独使用 BC 或 N 处理，N 和 BC 的联合施用导致土壤有机碳 (SOC)、总氮 (TN)、溶解有机碳 (DOC)、总溶解氮 (TDN) 显着增加和有效钾 (AK) 水平，同时还能提高 C 和 N 循环酶的活性。相比之下，这种组合处理不会影响土壤 pH 值或磷酸酶活性。BC 的应用没有显着影响微生物生物量，但它与整体微生物群落结构的变化有关，包括真菌/细菌比率和革兰氏阴性/革兰氏阳性菌比率的降低。这些变化还与相对放线菌丰度的增加和 cy19:0/18:1ω7c 比率升高有关。这些结果表明，N 和 BC 的组合施用因此不利于真菌的快速生长，土壤 AK、pH、TN 和 TDN 是影响土壤微生物群落结构的主要因素。虽然 BC 确实显着增加了 βG:(NAG LAM) 比率，但这与任何 N 介导的微生物限制无关。总的来说，我们的研究结果最终表明，结合施用 BC 和 N 肥可以提高土壤质量，同时支持更稳定的微生物群落结构和更活跃的土壤生物活性。