2017 ASHS Annual Conference

The shallow Abbotsford-Sumas aquifer, which is highly susceptible to contamination from leaching, underlies an intensive raspberry production area in the Fraser Valley, BC, Canada. The region is characterized by warm, dry summers, requiring irrigation inputs for raspberry production, and cool wet winters. Therefore nitrate leaching losses are a function of irrigation and nutrient management in the dry season and residual nitrate content in the soil profile in the wet season. Two consecutive randomized complete block design experiments were conducted with a range of nutrient and drip irrigation practices. Passive capillary wick samplers were installed at 55 cm depth below the raspberry rows and adjacent alleys to capture water and nutrient fluxes. In experiment 1 (2009-2012), four replications of 8 treatments included some combinations of N rate: 0, 50, 100 kg N/ha; irrigation management: unscheduled, scheduled to meet 100% ET demand; N source: fertilizer, manure; alley management: tillage or alley crop; fertilizer application method: broadcast (split) or daily fertigation for six weeks. In 2011, 15N label was added to four of the treatments: 100 and 50 kg N/ha with unscheduled irrigation, 50 kg N/ha with scheduled irrigation and 50kg N/ha fertigated. In experiment 2 (2013-2015), all treatments had a perennial alley crop and four replications of 8 treatments with some combinations of N rate: 0, 25, 50, 100kg N ha^-1; irrigation management: as in experiment 1; irrigation frequency: 1 or 2 days; and manure legacy (0N). There were no yield responses to any treatments. A perennial alley crop reduced total nitrate leaching from 45 kg N/ha to 5 kg N/ha. Scheduling irrigation to meet evaporative demand reduced total nitrate leaching losses by 50% mainly due to the difference in growing season drainage. Highest N losses were consistently from the manured plots (2009-2012) which persisted in the manure legacy treatment until 2015. There were also considerable ecosystem inputs, particularly from groundwater used for irrigation, (up to 71kg N/ha), and these along with atmospheric deposition and soil mineralisation influenced both the lack of plant responses and nitrate leaching to the aquifer. In a single year, fertilizer N inputs, as measured by the 15N label, accounted for only 3-9% of leached nitrate. Beneficial management for this production system would include a perennial alley crop, irrigation scheduled to meet evaporative demand and fertigated N inputs adjusted for ecosystem supply. These practices were demonstrated to substantially reduce nitrate leaching losses while maintaining crop yield.