GROWTH AND NO3- ACCUMULATION IN HYDROPONIC LETTUCE WITH NITRATE/AMMONIUM RATIOS IN TWO CULTIVATION SEASONS

Abstract

Lettuce (Lactuca sativa L.) is a leafy vegetable that generates important economic income in Mexico; however, high levels of nitrates (NO₃^-) can cause health problems because they generate carcinogenic compounds. An alternative to reduce the NO₃^- in leaves is replacing it with ammonium (NH₄⁺), which could benefit human health by lowering intake of NO₃^-. The objective of this study was to evaluate the growth and accumulation of NO₃^- in lettuce with different ratios of NO₃^-/NH₄⁺ in the nutrient solution in two growing seasons. The lettuces were grown in a floating root hydroponic system. The experimental design was completely randomized, under a 4 × 2 factorial arrangement, four ratios of NO₃^-/NH₄⁺ (100/0, 80/20, 65/35 and 50/50) and two seasons (Summer and Autumn), with a total of 8 treatments. The evaluated traits were dry weight of roots (DWR), of leaves (DWL) and total (DWT), leaf area (LA) and NO₃^- concentration in petiole. No significant differences were found between seasons in DWL, DWT and LA. In Autumn DWR increased 11 % compared to that of Summer. In Summer the NO₃^- content in petioles increased by 55 % compared to that of Autumn. The 100/0 ratio increased 25 % DWL, DW and LA, and 15 % NO₃^-in petiole. During the Summer, there was an increase of 4 % in DWL, DWT and LA by using the 100/0 ratio. When NH₄⁺ was used in the 65/35 and 50/50 ratios, growth was reduced by 25 % and NO₃^- accumulation in petiole by 15 %. In the Summer growing season, the application of 100/0 in lettuce plants increased growth. In the summer season the NO₃^- content in petiole increased twofold.