Optimization of Growth-stage Specific Nitrogen Fertilization Improves Strawberry Growth and Yield

Nitrogen (N) fertilization rate is generally based on growth stage to ensure optimal N fertilization in strawberry. The objective of this study was to determine optimal growth-stage specific N fertilization rates for ‘Florida Radiance’ and ‘Florida 127’ strawberry cultivars. Field experiments were conducted during 2014-2015 and 2015-2016 growing seasons using standard production practices in Florida. In the first season, five N rates of 0.2, 0.6, 1.0, 1.4 and 1.8 lb/acre/d were evaluated from the establishment to early harvest (Oct- Dec). In the second season, four N rates of 0.75, 1.0, 1.5 and 2.0 lb/acre/d were evaluated during the establishment (3 weeks), early harvest (Nov-Dec), and late harvest (Jan-Mar). All treatments received the same N rate of 1.0 lb/acre/d except the treatment periods described. In the first season, canopy width and crown diameter in Dec. maximized at 1.0 and 1.8 lb/acre/d for ‘Florida Radiance’ and ‘Florida 127’, respectively. This enhanced vegetative growth increased marketable yield not only during the early harvest but also during the late harvest. The highest marketable yield was recorded at 1.8 lb/acre/d for ‘Florida radiance’ and 1.4 lb/acre/d for ‘Florida 127’. Similarly, the second season’s maximum marketable yield for ‘Florida Radiance’ and ‘Florida 127’ was recorded at 1.5 and 1.0 lb N/acre/d applied from the establishment to early harvest. Both cultivars maximized marketable yield when fertilized within a range of 0.75-1.0 lb/acre/d during the late harvest. The application of N at rates 1.5 lb/acre/d or higher during the late harvest increased unmarketable yield by 41- 42% in both cultivars, limiting the increase in marketable yield by N fertilization. Although sap nitrate concentration in the late season treatments increased from 705 to 1450 ppm in ‘Florida Radiance’ and from 340 to 1233 ppm in ‘Florida 127’ with increasing N from 0.75 to 2.0 lb/acre/d, there was no correlation between sap nitrate concentration and marketable yield (r²= 0.008). These results suggest that marketable yield of strawberry is most responsive to N fertilization from the establishment to early harvest. Thereafter, N fertilization should be maintained relatively lower to improve the percentage of marketable yield and fertilizer use efficiency.