Responses of semi-vigorous apple rootstocks (MM106 and MM111) to different nitrate and ammonium ratios under soilless culture

In this study, the effects of nitrate (NO3-) to ammonium (NH4+) ratios on vegetative growth parameters, mineral uptake, physiological and biochemical responses of two semi-vigorous apple rootstocks (MM106 and MM111) in hydroponically grown under greenhouse conditions were evaluated. Treatments were five nutrient solutions of differing NO3-:NH4+ ratios as follows (100:0, 80:20, 60:40, 40:60, 20:80) and two apple rootstocks. After 120 days of treatment, parameters were determined. The NO3-:NH4+ ratios significantly affected the vegetative growth of MM106 and MM111 rootstocks. Rootstocks fertilized with a high NH4+ ratio produced larger leaves, longer roots, stems, and diameter, while the plants under NO3- treatment alone had smaller and shorter roots. N-form significantly influenced the uptake and utilization of essential plant nutrients in both rootstocks. Leaf concentrations of nitrogen (N), potassium (K), and calcium (Ca) were highest with NO3-. Leaf concentrations of phosphorous (P), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) increased as NH4+ supplied more of the N-ratio. The highest chlorophyll a and b and total chlorophyll were observed at the 20:80 NO3-:NH4+ ratio. In comparison, the lowest content was at the highest dose of NO3- (100:0) treatment. The highest soluble sugars were obtained in the leaves of MM106 and MM111 at the ratio of 80:20. Soluble sugars in the root of both rootstocks decreased by increasing the NH4+ ratios in the nutrient solution. Our results show that supplying rootstocks with high NO3- as N form can affect vegetative growth and mineral uptake at this stage of growth.