Commercial Fertilizer Source Affects Marketable Leaf Yield of Collards in NFT Hydroponic Culture

Abstract. The effect of three commercial fertilizers on leaf yield of Collards (Brassica oleracea, Acephala group ‘Champion’) was evaluated in a closed, nutrient recirculating ‘Nutrient Film Technique’ (NFT) hydroponic system. Seedlings raised in 1-inch rockwool cubes were transferred into rows (28 cm apart) of PVC Hydro-Troughs with 4.45 cm diameter holes at 20 cm spacing (along the row) at the first true-leaf stage. Seedlings were grown until harvesting, either with Peters Excel-CAL-MAG^® (CAL-MAG), Peters Peat-Lite Special^® (PLTE), or Peters General-Purpose Soluble Fertilizer^® (P-GP) containing 15-5-15, 15-16-17 and 20-20-20, respectively, as percent N-P₂O₅-K₂O. Nutrient solution from each fertilizer source was prepared to supply nitrogen (N) at 200 mg/liter. At 64 days after transfer to NFT culture, the 77-day old Collards plants were root-pruned, and the fertilizer solutions renewed. Forty-two days after root pruning, marketable leaf yield (young, fully expanded leaves) from the fertilizer treatments were compared. Significant differences were observed in leaf count, leaf fresh and dry weight (CAL-MAG > [PLTE = P-GP]) and leaf dry weight ratio (CAL-MAG > PLTE > P-GP) (P = 0.01). Differences in petiole sap nutrient content was significant for NO₃^–-N (PLTE > CAL-MAG [P = 0.01]; and P-GP > CAL-MAG [P = 0.05]), and potassium (CAL-MAG > [PLTE = P-GP]) (P = 0.01). Petiole sap sodium content also varied significantly with fertilizer treatment (CAL-MAG > P-GP > PLTE) (P = 0.05), and (CAL-MAG > [P-GP = PLTE]) (P = 0.01). Petiole NO₃^––N concentration indicates that N supply in nutrient solution was not the yield-limiting factor in this study. CAL-MAG, the only calcium (Ca)–supplying fertilizer of the three (38.3 mg Ca/liter), promoted greater marketable leaf yield than either PLTE or P-GP. Magnesium supply from CAL-MAG was 1.7 and 4-fold the amount from PLTE and P-GP, respectively.