Growth and nutrient uptake responses of ‘Seolhyang’ strawberry to various ratios of ammonium to nitrate nitrogen in nutrient solution culture using inert media
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 substrate and 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 highest vegetative 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 the optimal 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.