IRRIGATION AND N FERTILIZATION MANAGEMENT AFFECTS NITRATE LEACHING IN STRAWBERRY PRODUCTION

The annual strawberry (Fragaria × ananassa Duch.) production system used in the coastal valleys of central California is highly productive (often reaching fruit yields of 70 t ha^-1), and has been widely adopted around the world. Strawberry growers in this region have recently come under regulatory scrutiny for potential nitrate pollution of groundwater resulting from their production practices. In this study irrigation and N fertilization practices were monitored in a total of six commercial strawberry fields during the 2009-10 and 2010-11 production seasons. Irrigation volume and timing were documented using water meters. Crop evapotranspiration (ET_c) was estimated from daily reference evapotranspiration (ET_o) and crop canopy development as determined by infrared imaging. N fertilization records were obtained from cooperating growers. Crop N uptake was determined by monthly destructive plant sampling. Soil leachate NO₃-N was measured weekly using suction lysimetry from May through to August, the period during which most of the seasonal irrigation was applied. Irrigation management varied widely among fields, ranging from deficit irrigation to an estimated 175% of ET_c. N fertilization was similarly variable, with the seasonal total ranging from 141-476 kg ha^-1. Total seasonal crop N uptake averaged 163 kg ha^-1, with marketable fruit accounting for 46% of the total. Estimated summer NO₃-N leaching loss ranged from 1-67 kg ha^-1, averaging 33 kg ha^-1. Soil NO₃-N monitoring in the 2010-11 fields indicated that N loss over the winter may have exceeded summer NO₃-N leaching.