Long-term fate of nitrate fertilizer in agricultural soils

Abstract

Increasing diffuse nitrate loading of surface waters and groundwater has emerged as a major problem in many agricultural areas of the world, resulting in contamination of drinking water resources in aquifers as well as eutrophication of freshwaters and coastal marine ecosystems. Although empirical correlations between application rates of N fertilizers to agricultural soils and nitrate contamination of adjacent hydrological systems have been demonstrated, the transit times of fertilizer N in the pedosphere-hydrosphere system are poorly understood. We investigated the fate of isotopically labeled nitrogen fertilizers in a three-decade-long in situ tracer experiment that quantified not only fertilizer N uptake by plants and retention in soils, but also determined to which extent and over which time periods fertilizer N stored in soil organic matter is rereleased for either uptake in crops or export into the hydrosphere. We found that 61-65% of the applied fertilizers N were taken up by plants, whereas 12-15% of the labeled fertilizer N were still residing in the soil organic matter more than a quarter century after tracer application. Between 8-12% of the applied fertilizer had leaked toward the hydrosphere during the 30-y observation period. We predict that additional exports of 15 N-labeled nitrate from the tracer application in 1982 toward the hydrosphere will continue for at least another five decades. Therefore, attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers in agricultural systems and the nitrogen retention capacity of agricultural soils.nitrogen cycle | nitrate leaching | isotopic biogeochemistry

A lagged variable model for characterizing temporally dynamic export of legacy anthropogenic nitrogen from watersheds to rivers

“…4a). This result is consistent with a long-term field study using a 15 N tracer that showed 8-12 % of the applied 15 N fertilizer was exported to the hydrosphere in the succeeding 30-year period (Sebilo et al 2013). The majority (~95 %) of riverine export of annual NANI occurred in the succeeding 10 years (Fig.…”

“…2014). Nitrogen leaching from legacy sources has been recognized as a primary reason for these limited results, due to the long lag time (ranging from years to decades) elapsed between watershed N inputs and riverine export (Sebilo et al 2013;Sanford and Pope 2013;Tesoriero et al 2013). Exceedance of water quality targets has prompted regulatory agencies to reevaluate nutrient management standards, measures, and guidelines (Sharpley et al 2013).…”

“…However, the calibration procedures for these models contain considerable uncertainty since measured riverine N fluxes are a mixture of N and water sources with different ages and the lag time is often larger than the temporal extent of available calibration data (Meals et al 2010;Bouraoui and Grizzetti 2014). Due to the complexities of understanding transit time and biogeochemical mechanisms for N passing through the soil profile, vadose zone, and groundwater to the river network (Meals et al 2010;Hamilton 2012;Sebilo et al 2013), the N leaching lag effect is not well addressed and formulated in most current watershed mechanistic models (Meals et al 2010;Sanford and Pope 2013;Bouraoui and Grizzetti 2014). For example, values for groundwater residence time in the SWAT model range from 0 to 500 days, which is much lower than estimated residence times (years to decades) derived from stable isotope tracers (mainly 18 O and 3 H) (Iqbal 2002;Phillips and Lindsey 2003;Tesoriero et al 2013).…”

Long-term fate of nitrate fertilizer in agricultural soils is not necessarily related to nitrate leaching from agricultural soils

“…Sebilo et al (1) provide a unique long-term record of 15 NO 3 fertilizer fate that demonstrates N molecules from a discrete fertilizer application are transferred to soil organic matter (SOM) and subsequently mineralized over the course of approximately 100 y, during which they contribute to NO 3 leaching. The authors conclude "attempts to reduce agricultural nitrate contamination of aquatic systems must consider the long-term legacy of past applications of synthetic fertilizers" (1). Furthermore, Sebilo et al suggest that a recent decrease in anthropogenic N inputs to the Mississippi River Basin, without a concomitant decrease in riverine NO 3 loads, is consistent with their conclusion.…”

Ammonium fixation and release by clay minerals as influenced by potassium

“…For this reason the splitting of the nitrogen application rate is recommended for an efficient use of fertilizer-N (López-Bellido et al 2012). Nevertheless in the last years an increasing diffuse nitrate loading of surface water and groundwater has emerged as a major problem in many agricultural areas of the world, resulting in contamination of drinking water resources (Sebilo et al 2013). An option to minimize nitrate leaching is the use of ammonium-containing N fertilizers.…”