María L. Tapia, Werther Kern, Víctor H. Escalona y L. Antonio Lizana (Centro de Estudios Postcosecha (CEPOC), Facultad de Ciencias Agronomicas, Universidad de Chile, Santa Rosa 11315, La Pintana. P.O. Box 1004, Santiago, Chile. website: www.cepoc.cl
Hydroponic grown lettuce usually sold at 20 to 30 % higher prices at local consumers markets, compared with same soil grown type, both at equal presentation, which includes individually wrapped in plastic bag . Some concern have resulted by indications that hydroponic growing systems may induce higher nitrates content in lettuce and also that cost involved in its production would be adverse in their profit.
Espanola type of lettuce were purchased at local markets, or obtained directly from production field, and analyzed at the CEPOC post-harvest laboratory during the month of Jan and Feb. Nitrate levels in hydroponic grown lettuce (flood root system and “Nutrient film Technique” (NFT) fluctuated between 1344 and 3.839 mg/kg. none reached European Commission´s maximum tolerance levels of 4.500mg/kg (FW). Average cost registered per unit, was US$ 0,08 dl, compared with US$ 0,13 dl of conventional soil grown lettuce in Chile. Also we calculate the hydroponic cultivated lettuce water footprint being the in the level of 19 m3 ton-1, value very low compared to the soil extensive cultivation of 237 m3 ton-1. The reverse analysis of the obtained values, indicated an average level of productivity of 53 g of lettuce (one unit)/ liter of water used for the hydroponic grown lettuce compared to 13 liters to produce each unit in the soil grown system. (4 g/liter). If consider the return price to grower was $170 pesos/unit (0,28 US dl/unit) the unit profit per liter of used water (estimated value US $ $ 0,0017/L) the value in the hydroponic unit crop was US$ 170 per dollar, and the soil grown lettuce, US$ 13 per dollar invested in water.
Hydroponically grown Espanola type lettuce, uses less water/unit to grow (water footprint) had better appearance, less damage in peripheral external leaves, cleaner presentation and a better market quality than traditional soil grown ones.