Nitrogen Application, Uptake and Loss In California Strawberry Production

Strawberry (Fragaria x ananassa Duch.) is a major crop in coastal California, an area with widespread NO₃-N impairment of both surface water and groundwater.  A commercial field survey was begun in 2010 with the objectives of 1) determining the N uptake of day-neutral strawberry grown in an annual production system, and 2) evaluating current N fertilizer practices and the potential for N loss to the environment.  Thirteen fields of ‘Albion’ strawberry and 14 fields of a proprietary cultivar grown in the Watsonville-Salinas area were sampled at monthly intervals from March through August.  Root zone soil NO₃-N and total leaf N were determined at each sampling date.  At two sites for each cultivar whole plant sampling for biomass and biomass N was also conducted.  Leachate NO₃-N was monitored by automated suction lysimetry in 3 fields.  Cooperating growers provided data on seasonal N fertilization and fruit yield.  Crop N uptake was linear through the sampling period, averaging approximately 1.2 kg ha^-1 day^-1.  By the end of August total N uptake averaged 190 kg ha^-1 across the 4 biomass monitoring sites, with N content nearly evenly split between vegetative tissue and fruit.  Seasonal N application varied from 138 to 337 kg ha^-1, averaging 213 kg ha^-1; approximately half was applied as controlled release fertilizer at crown planting the previous fall, and the remainder was fertigated through drip irrigation during the production season.  Soil NO₃-N concentration below 10 mg kg^-1 was maintained in most fields from April through August, the period of intensive irrigation.  Leachate NO₃-N was correlated with root zone soil NO₃-N, and in-season N loss was modest.  Mean leaf N declined from and average of 32 g kg^-1 in March (before harvest initiation) to 27 g kg^-1 at the fruiting peak.  Seasonal fruit yield averaged 74 Mg ha^-1, compared to the state average of 68 Mg ha^-1.  Neither fruit yield nor leaf N was correlated with N fertilization rate.