The effect of nitrogen, water and alley management strategies on nitrate and water loss from the root zone in perennial red raspberry.

Groundwater nitrate (NO₃⁻) contamination is a growing, global concern. The Abbotsford Aquifer is vulnerable to NO₃⁻ contamination with its high NO₃⁻ levels, in large part, linked to intensive agriculture, including the production of red raspberry (Rubus idaeus L.). This study examined the impacts of nitrogen (N), water and alley management strategies in red raspberry production on NO₃⁻ and water loss from the root zone using passive capillary wick samplers (PCAPS) during the establishment year and the first cropping year. Irrigation regime had a significant impact on root zone losses, particularly in the second year, when, under fixed duration irrigation, more than 50% of total annual NO₃⁻ losses occurred during the growing season. Irrigation scheduled according to plant water demand achieved ~50% water savings, maintained adequate soil moisture and retained N in the root zone as plant available. This retention of N did not increase plant N uptake and high NO₃⁻ losses in response to the onset of fall rains indicated that the N-fertilizer rate of 100 kg N ha⁻¹ was in excess of plant requirements. In the mineral fertilizer plots, the recommended post-harvest soil test for NO₃⁻ did not measure levels that indicated environmental risk, likely due to growing season leaching not accounted for by this test. The experiment was also influenced by N contributions in the irrigation water, which in fixed duration irrigation, were up to 55 kg N ha⁻¹. The use of manure resulted in greater drainage losses, nitrate losses, residual soil NO₃⁻ and flow-weighted nitrate concentration than mineral fertilizer plots, indicating elevated environmental risk. These effects were compounded by annual manure re-applications. Annual and perennial cover crops grown in the alleys significantly reduced nitrate leaching losses compared to alleys managed by tillage. Delivery of N by a daily fertigation strategy may better match raspberry plant N uptake than two broadcast applications. Overall, plant response to treatments was limited, suggesting that N supplied by soil, water and deposition (together, ecosystem N supply) was meeting plant N requirements and that the alternative management strategies explored are viable options to improve efficiencies in raspberry production while reducing environmental impacts.Arts and Sciences, Irving K. Barber School of (Okanagan)Earth, Environmental and Geographic Sciences, Department of (Okanagan)Graduat