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Abstract
Strawberry (Fragaria ananasa) plants were grown in hydroponics in a greenhouse, where the supply of different ammonium (NH4+): nitrate (NO3−) ratios, was investigated to reduce the negative effect of alkalinity in nutrient solutions. The experiment was arranged in factorial combination with two factors, NH4+:NO3− ratios (0%:100%, 25%:75%, 50%:50%, 75%:25%, and 100%:0%) and bicarbonate (0, 25, 50, and 75 mM; NaHCO3). Plants treated with increasing bicarbonate concentrations exhibited significantly inhibited growth. In plants treated with NH4+ and NO3− simultaneously, there was a counteraction of the bicarbonate-induced growth suppression. Sole NO3− application in the presence of high bicarbonate resulted in poor growth and plant death due to high alkalinity. The adverse effect of alkalinity on SPAD values and maximal quantum yield of PSII photochemistry (Fv/Fm) alleviated with increasing proportion of NH4+ in nutrient solutions. The results showed that fruit numbers and yield of strawberry increased with elevation of NH4+ in nutrient solutions.