Nitrogen evolution and fate in a Canary Islands (Spain) sprinkler fertigated banana plot

Banana and other horticultural produce cultivation, together with the population increase, has led to coastal aquifer degradation in the Canary Islands. A detailed field study to track nitrogen degradation and transport through a banana plantation soil into the aquifer is presented. The main objective of the study is to understand and quantify the hydrological behavior of the system, and quantify nitrogen leaching. The hydrogeological study of the area shows that the thin terraced soil is set on top of several layers of fractured basalt down to a massive formation where the polluted aquifer is found. When water leaves the soil profile, it is likely to quickly percolate along the preferential paths (cracks) through the basaltic layers and it is intercepted by lateral interflow in a mixing ratio of 25% irrigation drainage plus 75% interflow, before it reaches the aquifer. The soil water balance shows that most of the drainage (18% of the total irrigation+rainfall) is produced during the crop highest water demand period and during the short rainy season when no irrigation is applied. Monitoring of the soil solution showed that very high nitrate concentrations (50–120 mg/l NNO3) are present throughout the experimental period. The high water fluxes and nitrate concentration at the bottom of the soil profile produce a yearly loss of 48–52% of the total N applied (202–218 kg N/ha per year). Monitoring of water from springs below the experimental area shows that the nitrate lixiviates are diluted around 60% before reaching the aquifer, after mixing with the lateral flow. Smaller and more frequent applications of both N and water would help to reduce the environmental impact of the system.