2019 ASHS Annual Conference

Compound fertilizers with high N, P or K analysis, and optimum levels of micronutrients contain inadequate concentrations of the latter for optimum plant growth when diluted for use as hydroponic nutrient solution. This study compares the effect of hydroponic nutrient solution composition on foliar nutrient interactions and growth (leaf dry weight [LDW] per plant) of collards (Brassica oleraceae L. Acephala Group). Seedlings were grown with either arGrow Complete™ Spruce commercial fertilizer (70% Arginine-nitrogen; SweTree Technologies AB, Sweden) at 200 mg N/liter or full-strength Steiner's solution (Steiner’s) in hydroponic culture (pH 6.5 – 7.2). Fertilizer treatment (FERT) comprised of arGrow at micronutrient concentration proportional to that supplied at 200 mg N/liter (low; (arG_[LM]) or equivalent to full-strength Hoagland's solution (optimum; arG_[OM]). No significant (p = 0.05) differences in leaf growth of collards between arG_[LM] and arG_[OM]. Steiner’s increased LDW significantly (p < 0.05) compared with arG_[OM], but not arG_[LM]. With the exception of K (Steiner’s > arG_[LM], p = 0.0201), FERT had no significant (p = 0.05) effect on foliar N, P, Ca, Mg and S. Increases in foliar Mn, Zn, Cu, B and Mo content at arG_[OM] compared with arG_[LM] were significant (p < 0.05). Vector analysis helped in assessing the interactions between foliar nutrient elements and growth. It compared the indices: relative LDW (W), nutrient concentration (A) and nutrient content (C) in a single nomogram, in which indices of the reference treatment (arG_[LM]) were normalized to 100. Despite lack of significant (p = 0.05) FERT effect, depressed W with arG_[OM] caused higher K, N, and moderate Ca, Mg and S accumulation compared to arG_[LM], consistent with a concentration effect. Leaf W, A and C of phosphorus decreased by 9%, 12 % and 20%, respectively, indicating antagonism, possibly by the observed excess accumulation of Zn and Mn, with A of 94% and 96%, and C of 76% and 36%, respectively. High Zn and Mn, but moderate B, Cu and Mo accumulation occurred with arG_[OM] compared to arG_[LM]. Steiner's (+35% W over arG_[OM]), enhanced the uptake of foliar deficient K, N, and Ca, in contrast to growth induced dilution of P, S and Mg. Compared with arG_[LM], foliar deficiency of Zn, Fe and Mo in Steiner's induced tissue accumulation; while Cu uptake reached steady state A and was non-limiting to growth.