Recoupling C and N cycles: a fertiliser template to synchronise N supply and limit C priming?

Despite their advantages in plant productivity, plant uptake from conventional nitrogen (N) fertilisers is around 50%. To test whether recoupling carbon (C) and N cycles can decrease losses and increase N use efficiency (NUE), four experiments were conducted. Two growth accelerator pot experiments in contrasting soils were conducted with N additions representing a range of molar C to N ratios (Cmol:Nmol; 0.5 to 11) formulated from urea (U) and waste-derived materials (sugarcane trash, Ct; pelletised beef manure, B; dairy digestate, D; insect larvae, L; protein meal from insect larvae, P; and anaerobic pond sludge, S) with and without a nitrification inhibitor (I). Two reaction vessel experiments were conducted for measuring N-transformation based on continuous on-line nitrous oxide (N2O) and carbon dioxide (CO¬2) monitoring, and soil analyses. Adverse impacts of these stoichiometric formulations on C priming were examined using natural abundance isotopic signatures. Relative to urea, higher N use efficiency (~2 to 3 times) was achieved with waste derived (i.e., D, S, B, and P) formulations with I, with and without C. Increased Cmol:Nmol ratio increased post-experiment N retention in the fertiliser layer and delayed N uptake by the plant. Carbon priming losses were least with formulation Cmol:Nmol from 3.1 to 6.2. Our results suggest waste-derived stoichiometrically tailored formulations with an inhibitor have potential to avoid soil C priming, deliver better NUE, decrease N leaching losses, and increase N stocks in the soil profile.

尽管传统氮肥可提升作物产量，但其植物吸收利用率仅约为50%。为探究碳（C）与氮（N）循环的重新耦合能否降低氮素损失、提升氮素利用效率（NUE），本研究开展了四组实验。两组促生长盆栽试验分别在两种性状差异显著的土壤中开展，供试氮素来源涵盖以尿素（U）以及多种废弃物基物料——包括甘蔗渣（Ct）、颗粒化牛粪（B）、奶牛粪沼液（D）、昆虫幼虫（L）、昆虫幼虫蛋白粉（P）与厌氧塘污泥（S）——配制的一系列摩尔碳氮比（Cmol:Nmol，范围0.5至11）的处理，且分别设置添加与不添加硝化抑制剂（I）的组别。两组反应容器试验用于测定氮素转化过程，试验基于一氧化二氮（N₂O）与二氧化碳（CO₂）的连续在线监测，并辅以土壤理化分析。本研究通过自然丰度同位素特征分析，探究了上述化学计量配比物料对碳激发效应的不利影响。相较于纯尿素处理，添加硝化抑制剂（I）的废弃物基物料配制处理（即D、S、B、P组）在不同碳氮比条件下，均实现了约2至3倍的氮素利用效率提升。碳氮比（Cmol:Nmol）的提升会提高试验后肥料层中的氮素留存量，并延缓植物对氮素的吸收。当碳氮比（Cmol:Nmol）处于3.1至6.2区间时，碳激发效应引发的碳损失最小。本研究结果表明，添加抑制剂的废弃物基化学计量定制配方，具备规避土壤碳激发效应、提升氮素利用效率（NUE）、降低氮素淋溶损失并提升土壤剖面氮素储量的应用潜力。