Weitzman Julie N, Brooks J Renée, Compton Jana E, Faulkner Barton R, Peachey R Edward, Rugh William D, Coulombe Robert A, Hatteberg Blake, Hutchins Stephen R
ORISE Fellow at Pacific Ecological Systems Division, US Environmental Protection Agency, Corvallis, Oregon, USA.
Pacific Ecological Systems Division, US Environmental Protection Agency, Corvallis, Oregon, USA.
Vadose Zone J. 2024 May 31;23(3):e20324. doi: 10.1002/vzj2.20324.
A substantial fraction of nitrogen (N) fertilizer applied in agricultural systems is not incorporated into crops and moves below the rooting zone as nitrate (NO ). Understanding mechanisms for soil N retention below the rooting zone and leaching to groundwater is essential for our ability to track the fate of added N. We used dual stable isotopes of nitrate ( N-NO and O-NO ) and water ( O-HO and H-HO) to understand the mechanisms driving nitrate leaching at three depths (0.8, 1.5, and 3.0 m) of an irrigated corn field sampled every 2 weeks from 2016 to 2020 in the southern Willamette Valley, Oregon, USA. Distinct periods of high nitrate concentrations with lower N-NO values indicated that a portion of that nitrate was from recent fertilizer applications. We used a mixing model to quantify nitrate fluxes associated with recently added fertilizer N versus older, legacy soil N during these "fertilizer signal periods." Nitrate leached below 3.0 m in these periods made up a larger proportion of the total N leached at that depth (52%) versus the two shallower depths (13%-16%), indicating preferential movement of recently applied fertilizer N through the deep soil into groundwater. Further, N associated with recent fertilizer additions leached more easily when compared to remobilized legacy N. A high volume of fall and winter precipitation may push residual fertilizer N to depth, potentially posing a larger threat to groundwater than legacy N. Optimizing fertilizer N additions could minimize fertilizer losses and reduce nitrate leaching to groundwater.
农业系统中施用的大量氮肥并未被作物吸收，而是以硝酸盐（NO₃⁻）的形式向下移动到根区以下。了解根区以下土壤氮素保留和向地下水淋溶的机制，对于我们追踪添加氮素去向的能力至关重要。我们使用硝酸盐（¹⁵N-NO₃⁻和¹⁸O-NO₃⁻）和水（¹⁸O-H₂O和²H-H₂O）的双稳定同位素，来了解2016年至2020年期间在美国俄勒冈州威拉米特河谷南部每隔两周采样一次的灌溉玉米田三个深度（0.8米、1.5米和3.0米）处驱动硝酸盐淋溶的机制。硝酸盐浓度高且¹⁵N-NO₃⁻值较低的不同时期表明，部分硝酸盐来自近期施肥。我们使用混合模型来量化在这些“肥料信号期”与近期添加的肥料氮相比，与较老的残留土壤氮相关的硝酸盐通量。在这些时期，淋溶到3.0米以下的硝酸盐占该深度总氮淋溶量的比例更大（约52%），而较浅的两个深度（约13%-16%）则不然，这表明近期施用的肥料氮优先通过深层土壤进入地下水。此外，与重新活化的残留氮相比，与近期肥料添加相关的氮更容易淋溶。大量的秋冬降水可能会将残留肥料氮推向深处，这对地下水构成的威胁可能比残留氮更大。优化肥料氮添加量可以最大限度地减少肥料损失，并减少硝酸盐向地下水的淋溶。
