Agro-industrial composts represent both a sustainable alternative to inorganic fertilizers and a waste recycling management tool. Albeit, there is still a great deal of uncertainty as to what extent their use can contribute to the global N₂O budget. Here, two different composts [olive waste “alperujo” (AC) and biosolid (BC)] were tested during a three-year period to evaluate changes in N pools (NH₄⁺ and NO₃⁻), N₂O emissions and key N-cycle associated genes [ammonia monooxygenase (amoA) and N₂O reductase (nosZ)] in comparison with a control, treated only with mineral fertilization. To that end, a low dose (equivalent to 17.8 kg per tree of AC or BC) and high dose (equivalent to 26.7 kg per tree of AC+ or BC+) was applied to each individual plot composed of nine olive trees without irrigation in a completely randomized design. N₂O emissions rates showed a high spatial and temporal variability and no significant changes were detected in N pools when comparing with the control. However, the fact that the soil treated with BC+ presented 20% more NO₃⁻ compared to the control after the second compost addition and that the low doses of both composts displayed about 30% less NH₄⁺ than the control, suggests different pathways in N mineralization. Moreover, the N balance showed that soils treated with AC used all N provided and in turn promoted native N consumption while soil amended with BC only consumed part of the exogenous N provided. The assessment of the bacterial amoA and nosZ genes reflected that it was tillage practices rather than fertilization which had the most significant impact on their abundance, decreasing this effect towards the end of the experiment. Our results showed that under Mediterranean conditions the use of agro-industrial byproducts do not contribute to N₂O emissions and therefore it could be potentially used as a replacement of inorganic fertilizers favouring a circular economy of zero waste.

农工业堆肥既是无机肥料的可持续替代品，也是废物回收管理工具。_{尽管它们的使用在多大程度上有助于全球 N 2} O 预算，仍然存在很大的不确定性。在这里，在三年期间测试了两种不同的堆肥 [橄榄废料“alperujo” (AC) 和生物固体 (BC)]，以评估 N 池（NH ₄ ⁺和 NO ₃ ^-）、N ₂ O 排放和关键N 循环相关基因 [氨单加氧酶 ( amoA ) 和 N ₂ O 还原酶 ( nosZ)] 与仅用矿物施肥处理的对照相比。为此，将低剂量（相当于每棵树 17.8 公斤的 AC 或 BC）和高剂量（相当于每棵树 26.7 公斤的 AC+ 或 BC+）应用到由九棵橄榄树组成的每个单独的地块上，完全没有灌溉。随机设计。N ₂ O 排放率表现出很高的空间和时间变异性，与对照相比，N 池中未检测到显着变化。_{然而，与第二次添加堆肥后的对照相比，用 BC+ 处理的土壤的 NO 3} ^-含量增加了 20% ，并且两种堆肥的低剂量显示的 NH ₄ ^{+减少了约 30%。}与对照相比，表明 N 矿化的不同途径。此外，N 平衡表明，用 AC 处理的土壤使用了所有提供的 N，进而促进了天然 N 的消耗，而用 BC 修正的土壤仅消耗了提供的部分外源 N。对细菌amoA和nosZ基因的评估表明，对它们的丰度影响最大的是耕作而不是施肥，在实验结束时降低了这种影响。我们的研究结果表明，在地中海条件下，农工副产品的使用不会导致 N ₂ O 排放，因此它可能被用作无机肥料的替代品，有利于实现零废物循环经济。