The 2011 ASHS Annual Conference

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.