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The nitrogen requirements of lettuce (Lactuca sativa L.) cultivars for obtaining plants of a high phenotypical quality and low nitrate foliar content were studied in this research. Butterhead (Divina and Prima cvs.) and loose-leaf (Grand Rapids and Brisa cvs.) lettuces were grown in a modified hydroponic floating system. Plants were subjected to four treatments differential of nitrogen and are in mg of nitrogen L-1 : solution 1: 100 NO 3-N; solution 2:150 NO 3-N and 50 NH 4 +-N; solution 3: 200 NO 3-N and 100 NH 4 +-N; solution 4: 250 NO 3-N and 150 NH 4 +-N meanwhile as base solution was used modified Hoagland II solution. Cultivar responses to treatments were different so much in growth as foliar nitrate content. While the greatest growth was observed in 'Grand Rapids' and 'Brisa' in solution 1 with the lowest nitrogen content in which NO 3-N only was supplied, the opposite was observed in 'Divina' and 'Prima' in solution 4 and where NO 3 and NH 4 + were supplied. These results showed that the nutritional requirements cultivars are different. Moreover, greatest plant growth was observed in cultivars where the foliar nitrate content was highest. High levels of nitrate in vegetable crops have been associated with human health problem. The four cultivars in all treatments showed foliar nitrate contents below the limits established by the European Commission Legislation. This study permit to optimize the growth under such conditions.

Aquaponics is the integration of aquaculture and hydroponic systems where, in general terms, the waste produced by aquatic organisms becomes nutrients through bacterial action for plant growth. Water consumption as well as the environmental impact in this type of system are lower compared to more traditional hydroponic and aquaculture counterparts, due to its dual productive nature and closed condition of the system allowing the reuse of water and fish waste. The present study evaluated the yield, nitrate concentration, microbiological and functional quality of lettuce (Lactuca sativa L.) grown in two production systems: aquaponics and hydroponics. At the same time, fresh mass gain and feed conversion ratio (FCR) of rainbow trout (Oncorhynchus mykiss) were assessed. Lettuces were grown in an aquaponic system using waste water from the fish system, as well as in a hydroponic system with nutrient solution (Hoagland II-modified) both for 21 days. At the end of this period, baby lettuce (8 and 12 cm of length) was harvested. The yield of lettuce grown in aquaponic system was 6.73% higher than that of grown in hydroponic system. Also aquaponically grown lettuce had lower nitrate concentration (1079 mg kg-1 FW) than hydroponically grown lettuce (1229 mg kg-1 FW). Lettuces grown in both systems showed no significant differences in the microbial and functional qualities. Rainbow trout in the aquaponic system increased 13.6 g over 27.1±0.8 g initial fresh weight, obtaining a FCR of 0.74 after the experiment. These results indicate that the aquaponic system used in the present study is a sustainable alternative for the production of high quality lettuce considering its high yield, lower concentration of nitrates and similar microbiological and functional qualities compared to hydroponic systems, while allowing simultaneous fish farming with a good feed conversion ratio (74 g of food was needed to produce 100 g of rainbow trout).

RESUMENSe realizó un cultivo hidropónico de tomate (Lycopersicon esculentum Mill.) en invernadero en el Campus Azapa de la Universidad de Tarapacá, con el objetivo de estudiar el efecto del ambiente controlado y la calidad del agua de riego sobre el rendimiento total y la calidad de los frutos de tomate. El ensayo contó con cuatro tratamientos: T1 solución nutritiva preparada con agua del río Lluta (CE 3,96 dS m -1 ; 7,1 ppm B); T2 solución nutritiva preparada con agua tratada (desalinizada y desborificada) + boro (CE 3,1 dS m -1 ; 7,1 ppm B); T3 solución nutritiva preparada con agua tratada + sulfato de magnesio (CE 3,96 dS m -1 ; 0,8 ppm B), y T4 solución nutritiva preparada con agua tratada (CE 3,1 dS m -1 ; 0,8 ppm B). El diseño fue de bloques completos al azar con cuatro repeticiones. Las plantas se cosecharon hasta el quinto racimo (120 días desde el trasplante), obteniéndose los siguientes rendimientos: T1 = 40 t ha -1 , T2 = 39 t ha -1 , T3 = 64 t ha -1 y T4 = 61 t ha -1 . Se observó que el exceso de boro de los tratamientos T1 y T2 produjo una disminución importante en el rendimiento total de tomate en un 40% y en el rendimiento comercial de un 55%. La totalidad de los tratamientos tuvo un rendimiento mayor al mejor rendimiento informado para los cultivos de tomate al aire libre en el valle de Lluta (30 Mg ha -1 ). Se concluyó que el cultivo hidropónico de tomate en invernadero en el valle de Lluta es una alternativa para aumentar los rendimientos de este cultivo, y que la principal limitante de este valle para el cultivo de tomate es el alto contenido de boro en sus aguas de riego.Palabras clave: Máximo rendimiento tomate, toxicidad por boro, agricultura Región de Tarapacá. ABSTRACT An hydroponic tomato crop (Lycopersicon

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