Growth, nutrient uptake and tipburn severity of hydroponic lettuce in response to electrical conductivity and K:Ca ratio in solution

Growth, nutrient uptake and tipburn severity of hydroponic lettuce in response to electrical conductivity and K:Ca ratio in solution

1994

A:PS

Head lettuce cultivars Coolguard and Fame and non-heading cv. Red Mignonette were grown to maturity in recirculating hydroponic culture with a standard nutrient formulation (with a K:N ratio of 1.7:1.0 and a K:Ca ratio of 1.25:1.00 (equivalent weight basis)) to examine the effect of electrical conductivity (EC, 0.4-3.6 dS/m) and, for the latter 2 cultivars, nutrient formulation K:Ca ratio (from 1.00:3.50 to 3.50:1.00) on growth, nutrient uptake and tipburn severity. Plants grown at an EC of 0.4 dS/m were N and K deficient, while recently matured leaves and youngest leaves contained the highest Ca concentrations which decreased with increasing EC. When Coolguard was grown at an EC of 1.0 dS/m, N and K deficiencies were eliminated and leaves contained the highest Ca concentration. The greatest leaf + head FW was recorded at 1.6 dS/m and the decline in nutrient solution N and K concentrations over the growth period was 13 and 42%, respectively. An increase in the K:Ca ratio of the formulation increased leaf FW by 13% and leaf + head FW at maturity by 10% for Fame, whereas for Red Mignonette, a reduction in the K:Ca ratio increased leaf FW by 29% compared with the standard formulation. A reduction in the K:Ca ratio increased the Ca concentration in the youngest leaves of Fame and Red Mignonette at 1.6 and 3.6 dS/m. Leaf K concentrations were generally reduced by low EC and low K:Ca ratio. Hot conditions led to tipburn developing in Red Mignonette at harvest in week 2. The number of leaves/plant with tipburn at maturity (week 3) decreased from 23.1 to 4.4 as EC was reduced from 3.6 to 0.4 dS/m, and from 15.2 to 12.3 as the nutrient solution K:Ca ratio was reduced from 3.5:1.0 to 1.25:1.00. Over the last week of the growth period, the number of leaves with tipburn remained stable at an EC of 0.4 dS/m, whereas at 3.6 dS/m the number of leaves with tipburn increased by 253%. Tipburn developed in young leaves of Red Mignonette which had a Ca concentration range from 1.7 to 3.2 g/kg and was generally absent from recently matured leaves which had a Ca concentration of 11.0 g/kg. Young leaves of the tolerant cv. Fame had a Ca concentration of 5.9 g/kg.

v.45(1):251-267, AUSTRALIAN JOURNAL OF AGRICULTURAL RESEARCH

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