Effect of Ammonium: Nitrate Ratio on Yield, Calcium Concentration, and Photosynthesis Rate in Strawberry

Abstract

ABSTRACT The effect of ammonium:nitrate (NH4:NO3) ratio in nutrient solution on growth, photosynthesis (Pn), yield, and fruit quality attributes in hydroponically grown strawberry (Fragaria × ananassa Duch) cvs. ‘Camarosa’ and ‘Selva’ was evaluated. There were four nutrient solutions of differing NH4:NO3 ratios as follows: 0:100, 25:75, 50:50, and 75:25. Plants grown in solution with 75% NH4 had lower leaf fresh and dry weights and leaf area than those with 25% NH4 in both cultivars. High ratios of NH4 and NO3 in the solution always reduced the yield. The yield was increased by 38% and 84% in ‘Camarosa’ and ‘Selva,’ respectively, when the plants were grown in the 25NH4:75NO3 solution compared with plants grown in a higher NH4 ratio solution. The increased yield at the 25 NH4:75NO3 ratio was the result of the increase in fruit size, i.e., length and fresh weight of fruits. Plants grown in the 25NH4:75NO3 solution had the highest rate of Pn, while those grown in 75NH4:25NO3 solution had the lowest Pn rates in both cultivars. Increasing the NH4 ratio in the solution from 0 to 75% significantly reduced the calcium (Ca) concentration and postharvest life of the fruits in both cultivars. Both higher leaf area and Pn rate appeared to be the reason for the increased yield and plant growth in the 25:75 ratios of nitrogen (N). The results indicate the preference of strawberry plant growth toward a greater nitrate N form in a hydroponic solution. Therefore, a combination of two forms of N in an appropriate ratio (25NH4:75NO3) appears to be beneficial to plant growth, yield, and quality of strawberry fruits.