Loss of nitrate-nitrogen (NO₃⁻–N) from Midwestern U.S. agricultural fields can impair water quality and be an economic loss to farmers. Winter cover crops have shown promise as a remedy, but low adoption illustrates the need for alternatives. Here, we tested whether adding a carbon (C)-rich soil amendment (i.e., crude glycerol, a biodiesel byproduct) can increase soil microbial biomass (MB) and promote N immobilisation under various conditions and then determined whether and when immobilised N would be released. We conducted a laboratory incubation with a full factorial combination of four glycerol rates (0, +117, +468 and +1872 mg C kg⁻¹ soil), three supplemental NO₃⁻–N rates (0, +10 and +40 mg N kg⁻¹) and two soils (Clarion clay loam and Sparta loamy sand). Soil inorganic N (NH₄⁺–N and NO₃⁻–N) and MB were measured at seven and three time points, respectively, across the 98 days incubation period. Across all treatments, glycerol increased MBN in both short term (7 days; 4%–1137% compared to no glycerol addition) and long term (98 days; 10%–169%) and decreased NO₃⁻–N with increasing rate of glycerol. Adding glycerol caused net N immobilisation of 21%–61% (+117 mg C kg⁻¹ addition) and ~100% (+468 and +1872 mg C kg⁻¹ addition) compared to the control. Some of that immobilised inorganic N was likely released through MB turnover, but timing and rate of release depended on the soil and added N rate. Adding 40 mg N kg⁻¹ with no glycerol showed nearly twice the net N mineralisation rate than with the low or no applied N – providing evidence for soil N priming. Overall, glycerol has the potential for use as a soil amendment to increase MB and temporarily immobilise NO₃⁻–N and then make some of that N crop available through MB turnover.

中文翻译：

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粗甘油，一种生物柴油副产品，用作土壤改良剂以暂时固定然后释放氮

美国中西部农田的硝酸盐-氮 (NO ₃ ^{- -N) 损失会损害水质并对农民造成经济损失。}冬季覆盖作物已显示出作为补救措施的希望，但低采用率表明需要替代品。在这里，我们测试了添加富含碳 (C) 的土壤改良剂（即粗甘油，一种生物柴油副产品）是否可以增加土壤微生物量 (MB) 并在各种条件下促进 N 固定，然后确定是否以及何时固定 N释放。我们用四种甘油比率（0、+117、+468 和 +1872 mg C kg ^-1土壤）、三种补充 NO ₃ ^- -N 比率（0、+10 和 +40 mg牛顿公斤^-1) 和两种土壤（Clarion 粘土和 Sparta 壤土）。土壤无机氮（NH ₄ ⁺ -N 和 NO ₃ ^- -N）和 MB 在 98 天的潜伏期内分别在 7 个和 3 个时间点测量。_{在所有处理中，甘油在短期（7 天；与不添加甘油相比4} %–1137%）和长期（98 天；10%–169%）均增加 MBN，^并随着甘油。添加甘油导致 21%–61%（+117 mg C kg ^-1添加）和 ~100%（+468 和 +1872 mg C kg ^{-1 ）的净 N 固定}添加）与对照相比。一些固定的无机氮可能通过 MB 周转释放，但释放的时间和速度取决于土壤和添加 N 的速度。添加 40 mg N kg ^-1而不含甘油，其净 N 矿化率几乎是低施氮或未施氮时的两倍——这为土壤 N 引发提供了证据。总体而言，甘油具有用作土壤改良剂的潜力，可增加 MB 并暂时固定 NO ₃ ^- -N，然后通过 MB 周转使部分 N 作物可用。