Quantification of Groundwater Nitrate Loading after Raspberry Field Renovation Using High‐Resolution Passive Diffusion Sampling

Abstract

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.

Agroforestry buffers on nitrogen reduction in groundwater on a grazed hillslope

“…(2019) found increases in the nitrate concentration for groundwater in 5‐m deep wells, during the fertilization period, in an agricultural watershed in Italy. An unconfined permeable aquifer under a raspberry field that was manure treated showed an annual N load increase by 32%, 240%, and 18% after 1, 2, and 3 years, respectively, of the manure application (Loo et al., 2019). Du et al.…”