The quantification of groundwater NO loading associated with a specific field or set of management practices so that groundwater quality improvements can be objectively assessed is a major challenge. The magnitude and timing of NO export from a single agricultural field under raspberry ( L.) production were investigated by combining high-resolution groundwater NO concentration profiles (sampled using passive diffusion samplers) with Darcy's flux estimation at the field's down-gradient edge (based on field-measured hydraulic gradients and laboratory-estimated hydraulic conductivity). Annual recharge estimated using Darcy's law (1002 mm) was similar to that obtained using two other approaches. The similarity in the rate of Cl applied to the field and the estimated export flux over the 1-yr monitoring period (51 vs. 56 kg Cl ha) suggested the mass flux estimation approach was robust. An estimated 80 kg NO-N ha was exported from the agricultural field over the 1-yr monitoring period. The greatest monthly groundwater mass flux exported was observed in February and March (∼11 kg NO-N ha), and was associated with NO leached from the soil zone during the onset of precipitation in the previous autumn. Provided the groundwater recharged from the field of interest can be isolated within a vertical profile, this approach is an effective method for obtaining spatially integrated estimates of the magnitude and timing of NO loading to groundwater.

Core Ideas NO3 leaching was quantified by passive capillary wick samplers over 2 yr. NO3 leaching was three times greater in Year 1 than Year 2 (240 vs. 80 kg N ha−1). Increased Year 1 NO3 leaching reflected field renovation prior to monitoring period. There was strong seasonality in NO3 leaching from the field. Despite fertilizer banding in rows, 60% of NO3 leached from alleys between rows. Groundwater NO3–N contamination in the Abbotsford‐Sumas Aquifer in British Columbia, Canada, has been attributed primarily to NO3–N leaching from red raspberry (Rubus idaeus L.); however, direct estimates of NO3–N leaching are lacking. This study quantified the magnitude and timing of NO3–N leaching under a commercial red raspberry field over 30 mo (October 2010–March 2013) using passive capillary wick samplers installed below the root zone at three row locations (irrigated row, nonirrigated row, and alley) after the critical period of field renovation and replanting. Substantial NO3–N leaching (240 kg N ha−1) during the first year of monitoring was attributed to the effects of field renovation (including autumn chopping and incorporation of raspberry canes and soil fumigation and spring poultry broiler manure application) in the year prior to the initiation of monitoring. Lower NO3–N leaching (80 kg N ha−1) occurred in the second year of monitoring under typical mineral fertilizer management practices. Strong seasonality of NO3–N leaching was observed in both years, with ∼48% in autumn, 34% in spring and summer, and 17% in winter. Approximately 60% of the NO3–N leaching was attributed to the alleys between raspberry rows, which did not receive mineral fertilizer or irrigation. The high proportion of leaching during spring and summer and from the alleys suggests that growing‐season irrigation practices and alley vegetation management, respectively, would be good targets for the development of improved practices. The samplers were effective in quantifying the magnitude and timing of NO3–N leaching from a commercial agricultural field and informing the development of improved practices.

Source nitrogen (N) identification of leachate or groundwater nitrate is complicated by N source mixing and N and oxygen (O) isotope fractionation caused by microbial N transformations. This experiment examined the δN and δO values in leachate collected over 1 yr at 55 cm below raspberry ( L.) plots receiving either synthetic fertilizer (FT) or poultry manure (MT). The large ranges of δN (FT: -2.4 to +8.7‰, MT: +1.6 to +9.6‰) and δO (FT: -9.9 to -0.3‰, MT: -10.9 to +1.7‰) values in leachate collected under crop rows prohibited the reliable identification of the applied N sources on individual sampling dates. However, the mass-weighted average δN (FT: +3.2‰, MT: +7.3‰) values in leachate were significantly different and can be explained by accounting for the estimated contributions of nitrate and δN values of the various N sources, including applied fertilizer (-0.7‰) or manure (+7.9‰), nitrate-rich irrigation water (+9.0‰), and nitrate from soil N mineralization and nitrification (FT: +3.7‰, MT: +4.6‰; the seasonal timing of which is unknown). This study illustrates the importance of characterizing all major N sources and considering the seasonal variation of these sources and of N cycling processes, as they contribute to the δN values of leachate.

The Abbotsford-Sumas Aquifer is a permeable, unconfined aquifer in British Columbia, Canada, where raspberry (Rubus idaeus L.) production is an important source of groundwater NO 3 contamination. Renovation of raspberry fields (i.e., canes chopped, soil tilled and fumigated, and spring manure application prior to replanting), which typically occurs every 6 to 10 yr in response to decreased crop vigor, has been suggested as a possible cause of significant interannual variation in groundwater NO 3 concentrations. This study used high-resolution passive diffusion sampling to quantify the magnitude and timing of NO 3 loading to shallow groundwater from a commercial raspberry field during a 6-yr (2009-2015) monitoring period after crop renovation. After renovation, the annual NO 3 loading increased from ?95 kg N ha −1 in Year 1 to ?245 kg N ha −1 in Year 2 and decreased to ?85 kg N ha −1 in Year 3. The average annual NO 3 loading from Years 4 to 6 (72 kg N ha −1 ) was assumed to reflect annual loading without a renovation effect, and the increased loading during Years 1 to 3 was attributed to renovation. Renovation contributed an estimated 33 to 23% of total groundwater NO 3 from this field for a 6-to 10-yr renovation cycle. Most of the NO 3 loading associated with renovation occurred in Year 2 and was attributed to the manure application. The increased NO 3 loading after renovation likely contributes to the spatial and temporally varying NO 3 patterns observed in the aquifer. Reducing manure applications during renovation and decreasing renovation frequency have the potential to decrease the groundwater NO 3 concentration.