Quantifying nitrate leaching under commercial red raspberry using passive capillary wick samplers
Citation
Loo, S.E., Zebarth, B.J., Ryan, M.C., Forge, T.A., Cey, E.E. (2019). Quantifying nitrate leaching under commercial red raspberry using passive capillary wick samplers. Vadose Zone Journal, [online] 18(1), http://dx.doi.org/10.2136/vzj2018.08.0152
Plain language summary
The Abbotsford-Sumas Aquifer, which underlies productive agricultural land in the Fraser Valley of BC and an adjacent portion of Whatcom County, Washington State. The aquifer is the source of drinking water for more than 100,000 residents but for several decades water in the aquifer has had elevated concentrations of nitrate. Agricultural activities, particularly raspberry production which is concentrated over the aquifer, appear to be the primary source of the nitrate. However, direct estimates of nitrate leaching from raspberry production are lacking. This study used novel Passive Capillary Wick Samplers to directly measure the magnitude and timing of nitrate leaching from a commercial red raspberry field near Abbotsford over 30 months, starting at the time of replanting the raspberry field. Three times more nitrate leached from the raspberry field during the first year after planting than in subsequent years. This result indicates that the processes of renovating and replanting fields, and fertilization of small plants in the first year, are critical points in the production cycle and would be good targets for the development of improved practices to reduce leaching. In all years, most of the leaching (48% of the annual total) occurred in autumn, as a result of heavy fall rains. However, considerable nitrate leaching also occurred in spring and summer (34% of annual total), suggesting that irrigation growing season irrigation practices also would be good targets for the development of improved practice.
Abstract
Groundwater NO 3 –N contamination in the Abbotsford-Sumas Aquifer in British Columbia, Canada, has been attributed primarily to NO 3 –N leaching from red raspberry (Rubus idaeus L.); however, direct estimates of NO 3 –N leaching are lacking. This study quantified the magnitude and timing of NO 3 –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 NO 3 –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 NO 3 –N leaching (80 kg N ha −1 ) occurred in the second year of monitoring under typical mineral fertilizer management practices. Strong seasonality of NO 3 –N leaching was observed in both years, with ~48% in autumn, 34% in spring and summer, and 17% in winter. Approximately 60% of the NO 3 –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 NO 3 –N leaching from a commercial agricultural field and informing the development of improved practices.