Abstract

The effect of the variation of NH₄⁺:NO₃⁻ratios (meq/l: 0:100, 40:60, 50:50, 65:35 and 100:0) in the nutrient solution on strawberry (Fragaria × ananassa var Seolhyang) growth was evaluated. A mixture of large particle size (2 to 5 mm) and small particle size (smaller than 1 mm) of perlite was used as growing substrateand the nutrient solutions were applied once a week to the root substrate. The growth responses were determined 120 days after transplanting. The use of NO₃⁻as the sole source of nitrogen in the nutrient solution resulted in the highestvegetative growth among the treatments tested. On the contrary, the exclusive use of NH₄⁺ in the nutrient solution suppressed plant growth severely. The initial symptoms of ammonium toxicity appeared on the lower leaves, with the curling down of the old leaves. The margins turned brown and finally died. The introduction of the two nitrogen forms as the treatment ratio 60:40 (NH₄⁺:NO₃⁻) resulted in theoptimal growth performance and nutrient uptake of this variety. The rate K/Ca+Mg=0.57, which was close to the best rate 0.67, allowed the optimal uptake of all nutrients. The data of the growth characteristics, nutrient content and electrical conductivity (EC) and pH were subjected to a polynomial regression analysis. The results show a high correlation between these data and the variation of NH₄⁺:NO₃⁻ratios. The values of the fresh and dry weight and N content of above-ground plant tissue to this variation were linear, with R² coefficients of 0.95***, 0.94**, and 0.71*. The changes in the NO₃⁻ concentration in the petiole sap, EC and pH of the root substrate were quadratic, with a coefficients of R²= 0.99***, 0.98***, and 0.73*.

Key words: Growth characteristics, NH₄⁺: NO₃⁻ ratios, nutrient content, strawberry.