Nitrogen form and light intensity are two critical factors influencing the vegetative growth and physiological responses of strawberry (Fragaria × ananassa Duch.). Balanced nitrate (NO₃⁻) and ammonium (NH₄⁺) nutrition can improve nitrogen assimilation and biomass accumulation, while moderate shading helps mitigate light and temperature stress in nursery systems. However, the interaction between these factors and their combined influence on mother and daughter plant performance has been less documented. Therefore, this study aimed to investigate the effects of different shading intensities and nitrate-to-ammonium ratios on growth traits, root and leaf biomass, and leaf nitrogen content of strawberry plants to determine the most favorable conditions for producing vigorous and nutrient-efficient transplants.

Materials and Methods

The experiment was conducted under field-controlled conditions at Sari Agricultural Sciences and Natural Resources University. Strawberry runner plantlets from commercial nursury were transplanted to soil beds in March, and two shading levels (30% and 50%) and four nitrate-to-ammonium ratios (0:100, 25:75, 50:50, and 75:25) were applied in a factorial design. Watering, flower removal, and fertilization were performed during spring, and shading nets were installed in July. Morphological traits including root and leaf fresh and dry weights, plant height, crown diameter, number of roots, leaves, and stolons, leaf area, and leaf nitrogen concentration were measured separately for mother and daughter plants.

Results and Discussion

Statistical analysis revealed significant effects of both shading and nitrogen form, as well as their interaction, on most evaluated traits. In daughter plants, the highest root fresh (0.543 g) and dry weights (0.24 g) were obtained under 50% shading with a 75:25 nitrate-to-ammonium ratio, showing no significant difference from 25:75 at the same shading level. The lowest root biomass (0.001 g) was recorded in the 75:25 treatment without shade. Plant height was also strongly affected, reaching its maximum (12.5 cm) at 75:25 and 11.9 cm at 100:0 under 50% shading, representing 56–58% increases compared to the control. Fresh leaf weight peaked at 0.77 g in the 0:100 treatment under 50% shading—a 74% improvement over control—while 75:25 and 25:75 ratios achieved 66–68% increases. Fresh crown weight reached 0.42 g under 25:75 at 50% shading, while the lowest value (0.16 g) occurred in 0:100 with 30% shading. For mother plants, the analysis of variance indicated a significant interaction between shading and nitrogen treatments for most growth parameters (root number, root biomass, leaf number, leaf area, stolon number, crown diameter, and leaf nitrogen content). The greatest root number (34.83) was found under 30% shading without nitrogen fertilization. The 50:50 ratio exhibited the best overall root performance, with maximum root fresh weight (3.06 g) under no shading and the highest dry weight (1.68 g) under 30% shading. The highest leaf count (10.5 leaves) was recorded at 30% shading without nitrogen supply, whereas 50% shading caused a marked decline. Leaf area reached its maximum (64.75 cm²) under 30% shading with the 50:50 ratio, showing a 34% increase relative to the control, while the lowest (17 cm²) occurred in the 75:25 treatment without shading. Crown diameter was greatest (1.25 cm) under 50% shading with the balanced 50:50 ratio, suggesting that moderate shading combined with equal nitrate and ammonium supply enhances stem thickening. Stolon production was favored by 30% shading, with the highest number (8.33 stolons) in the 25:75 ratio, whereas excessive shading (50%) reduced stolon formation. Leaf nitrogen concentration peaked at 2.64% in 30% shading with 0:100 (pure ammonium), showing a 32% increase compared with the control, while lower values (1.34–1.36%) were associated with 25:75 and 50:50 ratios under the same shading level.

Conclusion

This study demonstrates that integrating moderate shading (30%) with a balanced nitrate-to-ammonium ratio (50:50) significantly enhances nitrogen uptake, biomass accumulation, and morphological traits in both mother and daughter strawberry plants. The combined management of light and nitrogen form can therefore be a practical strategy to produce healthy and vigorous transplants with improved nutrient efficiency and growth uniformity.

Acknowledgement

We hereby express our sincere appreciation to Turine Baft Shomal Company, central lab, expert men and women and the GABIT institute (Genetics and Agricultural Biotechnology Institute of Tabarestan) for their collaboration in providing the necessary support for this research in SANRU (Sari Agricultural and Natural Resources university), college of agronomy sciences department of horticultural sciences as a Master of sciences thesis.