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Universidade de Sao Paulo Brazil 2007

Use of brackish waters for lettuce production in NFT hydroponics system as a suitable agricultural alternative to Brazilian semi-arid / Utilização de águas salobras no cultivo da alface em sistema hidropônico NFT com alternativa agrícola condizente ao semi-árido brasileiro

Soares Tales Miler

Titre : Use of brackish waters for lettuce production in NFT hydroponics system as a suitable agricultural alternative to Brazilian semi-arid / Utilização de águas salobras no cultivo da alface em sistema hidropônico NFT com alternativa agrícola condizente ao semi-árido brasileiro

Auteur : Tales Miler Soares

Université de soutenance : Universidade de Sao Paulo

Grade : Doutorado 2007

Résumé
Several times, the extensive agriculture fails under semi-arid conditions in the Northeast region of Brazil, where the surface water is shortage and the pluvial precipitation is irregular. The use of groundwaters could increase the crops yield. However, due to the geological factors, it is usual the occurrence of brackish groundwaters in this region. The utilization of these waters would carry to soil salinization. Moreover, the opened deep tubewells often have low capacity. In this scenario, the hydroponics systems may be suitable to intensive production based in reduced areas. The higher water use efficiency in soilless cultivation is a well reported advantage, because in this system the water loss by evaporation is minimum. In hydroponics systems could be increase the crop salt tolerance. This would permit the brackish water use and, as an extra benefit, would increase the environmental safety. In hydroponics system, there is no the matric potential, which decreases the free-energy of water. Furthermore, the hydroponics structure operates as a drainage system. The accumulated salts, at the end of the period, may be easily removed from system. In order to test this hypothesis, were carried out experiments to evaluate the lettuce (cv. Verônica) salt tolerance under soil and hydroponics conditions. It was constructed a structure (40 independent experimental units) to simulate the Nutrient Technique Film (NFT) cultivation. For the soil experiment, it was used 12 L recipients and plastic mulch. It was registered that is feasible use waters more brackish in NFT system than in soil. For available of brackish and nonsaline waters, it was more productive to use non-saline water to prepare the nutrient solution and brackish water to supply the water consumption. Higher yield losses were observed with the use the brackish water to prepare nutrient solution and the non-saline water to replace the water consumption. The nutrient solution salinization was less depreciative to yield than the constant salinity. This finding was providing by the lettuce precocity. In relation to the salt tolerance in NFT system, the lettuce salinity threshold was estimated in 4.03 dS m-1. Under the same experimental conditions, the tolerance in soil was estimated in 2.51 dS m-1. These results confirmed the hypothesis and permit to present an agricultural alternative suitable to reality of many isolated families in Brazilian semi-arid.

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Page publiée le 4 avril 2010, mise à jour le 11 juillet 2017