Changes in the Concentration of Leaf Nitrogen over the Season Affect the Diagnosis of Deficiency or Sufficiency in Strawberries in the Subtropics

Optimum leaf nitrogen (N) concentrations have been identified for strawberry ( Fragaria × ananassa Duch.) in temperate and Mediterranean areas, but whether these values are appropriate for the subtropics is unclear. Two experiments were conducted for 2 years to determine if the seasonal changes in the concentration of leaf N affect the diagnosis of deficiency or sufficiency of strawberry plants in Queensland, Australia. In 2014, ‘Festival’, ‘Fortuna’, and ‘Winter Dawn’ were planted in early April and grown with and without N for the entire season. Then, ‘Festival’ was planted the following year in mid- or late April and, again, was grown with and without N. Yield was slightly lower with N in 2014, but higher with it the following year, particularly in the early planting. The concentration of total N in young, fully expanded leaves decreased from 3.0% to 2.0% as leaf, crown, and root dry weight increased, while the concentration of nitrate-N (NO 3 -N) decreased from 1200–3200 to 50–500 mg/kg. These changes in leaf N were large enough to affect the diagnosis of N deficiency or sufficiency. The concentration of leaf N was less variable than the concentration of leaf NO 3 -N and, therefore, better for estimating the nutrient status of strawberry plants in the subtropics.