Mineral Nutrient Stress Altered Growth and Yield of Collards Leaves in NFT Hydroponic Culture

Abstract.  Growth and yield response of collards leaves to mineral nutrient stress was evaluated in NFT hydroponic culture over a 68-day cropping cycle.  Seedlings of collards (Brassica oleracea, Acephala ‘Champion’) raised in 2.5 cm rockwool cubes were transferred into NFT culture at the second true-leaf stage and grown for 16 days in a conditioning nutrient solution prepared from a complete fertilizer (15N–2.2P–12.5K at 200 mg N liter^-1 plus micronutrients [C₁]).  From days 17 to 68 after transfer (DAT) into NFT culture, three nutrient treatments were initiated by replacing the conditioning nutrient solution (C₁) with either irrigation water from a well water source (C₁–C₀), a fresh C₁ solution (C₁–C₁), or 15N–2.2P–12.5K at 300 mg N liter^-1 (C₁–C₂). Water loss due to evapotranspiration was continuously replenished from the same source used to prepare the nutrient solution.  At 37 days after initiation of nutrient treatment (DNT), nutrient stress (C₁–C₀) caused significant (p < 0.05) reduction in marketable yield (fresh weight of young, fully expanded leaves [LFW]), leaf dry weight (LDW), leaf area (LA) and leaf chlorophyll content (LCC) compared with C₁–C₁ and C₁–C₂.  Specific leaf area (SLA) was significantly (p < 0.05) increased in C₁–C₀ compared with C₁–C₂, but not C₁–C₁; and leaf water content (LWC) was not affected by nutrition regime.  By 68-DNT, all the above parameters were significantly lower in C₁–C₀ compared with C₁–C₁ and C₁–C₂.  Whereas LDW decreased and LCC remained unchanged from 37 to 68-DNT; LFW, LWC, LA and SLA increased significantly (p < 0.05) in C₁–C₂.  Both in C₁–C₀ and C₁–C₁, LFW, LDW and LA declined very significantly from 37 to 68-DAT, but LWC, LCC and SLA were not affected at C₁–C₁.  Mineral nutrient stress significantly decreased leaf succulence, and consequently fresh weight yield of collards during a 68-day cropping cycle despite culture in liquid hydroponic system.