Denitrification is a key process buffering the environmental impacts of agricultural nitrate loads but, at present, remains the least understood and poorly quantified sink in nitrogen budgets at the watershed scale. The present work deals with a comprehensive and detailed analysis of nitrogen sources and sinks in the Burana–Volano–Navigabile basin, the southernmost portion of the Po River valley (Northern Italy), an intensively cultivated (> 85% of basin surface) low-lying landscape. Agricultural census data, extensive monitoring of surface–groundwater interactions, and laboratory experiments targeting N fluxes and pools were combined to provide reliable estimates of soil denitrification at the basin scale. In the agricultural soils of the basin, nitrogen inputs exceeded outputs by nearly 40% (~ 80 kg N ha⁻¹ year⁻¹), but this condition of potential N excess did not translate into widespread nitrate pollution. The general scarcity of inorganic nitrogen species in groundwater and soils indicated limited leakage and storage. Multiple pieces of evidence supported that soil denitrification was the process that needed to be introduced in the budget to explain the fate of the missing nitrogen. Denitrification was likely boosted in the soils of the studied basin, prone to waterlogged conditions and consequently oxygen-limited, owing to peculiar features such as fine texture, low hydraulic conductivity, and shallow water table. The present study highlighted the substantial contribution of soil denitrification to balancing nitrogen inputs and outputs in agricultural lowland basins, a paramount ecosystem function preventing eutrophication phenomena.

反硝化是缓冲农业硝酸盐负荷对环境影响的关键过程，但目前，在流域规模的氮收支中，反硝化作用仍然是了解最少且量化不足的汇。目前的工作涉及对 Burana-Volano-Navigabile 盆地的氮源和汇进行全面和详细的分析，该盆地是 Po 河流域（意大利北部）的最南端，这是一个集约化种植（> 85% 的盆地表面）低说谎的风景。农业普查数据、对地表-地下水相互作用的广泛监测以及针对 N 通量和池的实验室实验相结合，以提供流域尺度土壤反硝化的可靠估计。在流域的农业土壤中，氮投入超过产出近 40%（约 80 kg N ha ^-1年^-1)，但这种潜在的 N 过量状况并没有转化为广泛的硝酸盐污染。地下水和土壤中无机氮物种的普遍稀缺表明泄漏和储存有限。多项证据支持土壤反硝化是需要在预算中引入以解释缺失氮的命运的过程。由于质地细、水力传导率低和地下水位浅等特殊特征，所研究盆地的土壤可能会促进反硝化作用，容易出现淹水条件，从而限制氧气。本研究强调了土壤反硝化对平衡农业低地盆地氮输入和输出的重大贡献，这是防止富营养化现象的重要生态系统功能。