Quantification of groundwater nitrate loading after raspberry field renovation using high-resolution passive diffusion sampling
Loo, S.E., Zebarth, B.J., Ryan, M.C., Malekani, F., Cey, E.E., Suchy, M., Forge, T.A. (2019). Quantification of groundwater nitrate loading after raspberry field renovation using high-resolution passive diffusion sampling. Journal of Environmental Quality, [online] 48(6), 1722-1731. http://dx.doi.org/10.2134/jeq2019.01.0022
Plain language summary
Long-term monthly monitoring of nitrate concentration in groundwater was conducted in the Abbotsford-Sumas aquifer. In some wells, large changes in nitrate concentrations were measured over time, however he reason for this variation was not clear. It was thought that renovation of raspberry fields may be a cause of these changes in nitrate concentrations. Raspberry fields are renovated every 6 to 10 years in response to reduced crop vigor. Renovation typically include chopping and tilling the old raspberry canes into the soil, fumigating the soil, and applying manure in the spring prior to replanting. In this study, we measured the nitrate loading to groundwater for six years to capture loading during a renovation cycle. Field renovation greatly increased nitrate loading, largely in response to the manure application. The results of this study suggest that field renovation is a likely source of variation in groundwater nitrate concentration. The study also found that reducing manure applications during renovation and decreasing renovation frequency have the potential to decrease the groundwater nitrate concentration.
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 NO3 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 NO3 concentrations. This study used high-resolution passive diffusion sampling to quantify the magnitude and timing of NO3 loading to shallow groundwater from a commercial raspberry field during a 6-yr (2009-2015) monitoring period after crop renovation. After renovation, the annual NO3 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 NO3 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 NO3 from this field for a 6- to 10-yr renovation cycle. Most of the NO3 loading associated with renovation occurred in Year 2 and was attributed to the manure application. The increased NO3 loading after renovation likely contributes to the spatial and temporally varying NO3 patterns observed in the aquifer. Reducing manure applications during renovation and decreasing renovation frequency have the potential to decrease the groundwater NO3 concentration.