Mineral Nutritional Status and Yield of Swiss Chard in Hydroponic Culture as Influenced by Nutrient Solution Management and Seed Propagation Substrate

The influence of nutrient solution renewal (RNWL) versus replenishment of depleted nutrients (RPLN), and seed propagation substrate (SBSTR) on leaf mineral nutrient content and yield of Swiss chard (Beta vulgaris L. ‘Lucullus’), were evaluated in a Nutrient Film Technique (NFT) hydroponic culture. Seedlings at the second true-leaf stage were transferred into NFT culture and grown with a soluble fertilizer solution (15N–2.2P–12K) at 200 mg·L^-1 of N. The treatments comprised of two SMGMT techniques (RNWL and RPLN), and two seed propagation substrates (Oasis™ or Rockwool cubes). Laboratory leaf analysis at 63 days after transfer (DAT) into NFT culture indicates significant (P =0.05) SMGMT × SBSTR interaction for leaf nitrogen (N) and manganese (Mn) only. With RNWL, leaf N was higher in Rockwool than Oasis, whereas with RPLN N was highest in Oasis (P ≤0.05). Compared with Oasis, Rockwool increased leaf phosphorus (P), calcium (Ca) and magnesium (Mg) with RPLN (P ≤0.05), but not potassium (K) and sulfur (S). Besides N, SBSTR had no effect on leaf macronutrient content with RNWL. Across SBSTR, while leaf K was increased (P ≤0.01) by RPLN, leaf Ca was highest with RNWL (P ≤0.05); SMGMT did not affect the other macronutrients. Across SMGMT Rockwool increased leaf Mg (P ≤0.02) compared with Oasis, but no other macronutrient was affected by SBSTR. Of the micronutrients only leaf iron (Fe) content was affected by SBSTR within RNWL, being higher (P ≤0.05) in Rockwool than Oasis. Within RPLN Rockwool increased (P ≤0.02) the other micronutrients over Oasis, except copper (Cu) and molybdenum (Mo). With the exception of zinc (Zn) and Cu (RPLN > RNWL; P≤0.003), SMGMT had no effect (P ≤0.05) on the other micronutrients across SBSTR. Across SMGMT Rockwool increased leaf Fe, Mn, boron (B) and Al content over Oasis (P ≤0.02). Leaf growth and yield at 63-DAT indicates significant (P = 0.05) SMGMT × SBSTR interaction for leaf fresh- and dry weight (LFW, LDW [g]), but not leaf count (LC) and leaf area (LA; cm²) per plant. Within SMGMT LFW and LDW were higher in Rockwool than Oasis with either RNWL or RPLN (P≤0.01). Across SBSTR, RNWL increased LC and LA over RPLN (P≤0.01). Similarly, across SMGMT, LC and LA were higher in Rockwool than Oasis (P≤0.01). These observations suggests that RNWL with Rockwool substrate provided better growing conditions for optimum mineral nutrition and yield of Swiss chard in NFT hydroponic culture under the conditions of this experiment.