Nitrogen, irrigation, and alley management effects on nitrate leaching from raspberry
Kuchta, S., Neilsen, D., Forge, T., Zebarth, B.J., Nichol, C. (2020). Nitrogen, irrigation, and alley management effects on nitrate leaching from raspberry. Vadose Zone Journal, [online] 19(1), http://dx.doi.org/10.1002/vzj2.20054
Plain language summary
Commercial raspberry production in the Fraser Valley of British Columbia includes the use of synthetic fertilizers and manures to ensure that plants have adequate nutrients, particularly nitrogen, to produce high yields of quality fruit. If fertilizer applications provide nitrogen in excess of plant needs, however, then excess nitrogen remaining in the soil is prone to being converted to nitrate and leached from the soil into the underlying Abbotsford-Sumas aquifer. This research project used special devices called lysimeters to directly measure nitrate leaching from the root zone of raspberry plants subjected to different nitrogen fertilizer application rates, types of fertilizers (synthetic vs manure), methods of scheduling irrigation, with or without cover crops growing in alleyways between the raspberry rows. The aim of the project was to identify combinations of practices that minimized the likelihood of nitrate leaching. Results of the study indicated that scheduling irrigation based on the actual weather rather than on a calendar basis resulted in less water use and less nitrate leaching. Surprisingly, within the range of fertilizer application rates considered in the study, application rate had no effect on nitrate leaching, but more nitrate was leached from raspberry plants treated with poultry manure than synthetic fertilizer. Of all practices studied, the presence of a perennial grass alley cover crop resulted in the greatest overall reduction in nitrate leaching. Overall, the results indicate that an integrated package of improved practices including the use of weather-based irrigation scheduling and perennial alley cover crops, is necessary to protect groundwater quality under raspberry fields.
High NO3 concentrations in the Abbotsford-Sumas aquifer are linked to raspberry (Rubus idaeus L.) production. Passive capillary wick samplers were used to quantify the impacts of N, irrigation, and alley managements on drainage and NO3 leaching from raspberry rows and alleys over 4 yr. Conventional management (100 kg N ha−1 surface broadcast on the row as a split application, clean cultivation of alleys, and fixed-duration drip irrigation) was compared with different mineral fertilizer N rates, N applied as manure, alleys seeded to a perennial forage grass or an autumn-seeded spring barley (Hordeum vulgare L.) crop, or evapotranspiration (ET)-scheduled irrigation. The temporal pattern of drainage and NO3 leaching was driven by seasonal precipitation and growing season irrigation. Growing season drainage and NO3 leaching were much lower under ET-scheduled irrigation compared with fixed irrigation. Nitrate leaching was high (up to 90 kg N ha−1), even with no managed N inputs due to high inherent soil fertility and large quantities of N applied in irrigation water. Nitrate leaching was insensitive to N fertilizer rate. Application of N as poultry manure more than doubled NO3 leaching compared with fertilizer, emphasizing the need to use organic N inputs judiciously. The perennial grass alley cover crop resulted in the greatest overall reduction in NO3 leaching. Our data indicate that no single management strategy is sufficient to protect groundwater quality. Rather, an integrated package of improved practices (i.e., application of a reduced rate of mineral N through fertigation, combined with ET-scheduled irrigation and perennial alley crop) is necessary to protect groundwater quality.