Growth, mineral nutrient composition, and enzyme activity of strawberry as influenced by adding urea and nickel to the nutrient solution

BACKGROUND: Nutrient solution composition affects plant growth, yield and fruit quality. Nitrate, ammonium and urea are absorbable forms of nitrogen for plants however each form can have different effects on plant growth aspects. Urea is a low cost source of nitrogen and urease enzyme is activated by nickel (Ni), so using these nutrients may be beneficial for strawberry plant growth. The influence of different nutrient solution on strawberry cv. “Paros” growth, enzymatic activity and leaf mineral content was studied in this research at Shiraz University, Shiraz, Iran. OBJECTIVES: This study aimed to understand the role of Ni and different forms of nitrogen in the hydroponic culture on growth, nutrient composition and enzyme activity of strawberry plants, to identify whether a combination of different nitrogen form, especially urea and Ni, would improve plant growth and quality. METHODS: The effects of nitrate: ammonium: urea ratios (75:25:0, 50:25:25, 25:25:50, 25:0:75 and 0:0:100) and nickel sulfate concentration (0, 1 and 2 mg/L) in nutrient solutions were evaluated on strawberry cv. ‘Paros’ growth, mineral nutrient, and enzymatic activity. The trial was laid out as a factorial experiment with a completely randomized design. Rooted strawberry daughter plants were potted in 3 liter pots filled with cocopeat: perlite (1:1). Application of treatments started after establishment of the plants and continued for 5 months. RESULTS: Urea (25% and 50%) and nickel (1 mg/L) adding in the nutrient solution improved plant shoot and root dry weights. However, greater urea concentrations in the nutrient solution decreased nitrogen, potassium and phosphorous contents in leaves, but increased iron concentration. Urea concentration in strawberry leaves decreased when nickel concentration in the nutrient solution increased. Nitrate content in leaves of urea-fed plant decreased when urea concentration in nutrient solution increased. Urease activity increased with adding urea to the solution; however nitrate reductase activity was low at a high level of urea in nutrient solution. CONCLUSION: In addition to nitrate, adding nickel and urea in the nutrient solution improved growth and the enzymatic activity of strawberry plants, however it appeared that a higher rate of nickel and using urea as the only source of nitrogen was less beneficial. Overall, the best result was obtained from nickel at 1 mg/L and N source ratio of nitrate (50): ammonium (25): urea (25).