Effect of different substrates in aquaponic lettuce production associated with intensive tilapia farming with water recirculation systems

ABSTRACT The integration of fish farming in intensive system and plant production, called "aquaponics" is practiced successfully in countries like the USA, Australia and Europe. In Brazil, this integration has attracted the attention of researchers and producers. In this context, the aim of this study was to evaluate the effect of two substrates (crushed stone number 3, CS III and flexible polyurethane foam, FPF) on the production of aquaponic lettuce, moreover, to show that the residual water from intensive tilapia production provides sufficient qualitative characteristics for competitive production of lettuce without adding commercial fertilizers. The treatment in which FPF was used provided higher concentrations of macro and micronutrients in the shoots, higher production of fresh matter of shoots (95.48 g plant-1) and a larger number of leaves (14.90) relative to CS III. These results were attributed to the lower post-transplanting stress and the higher water retention time provided by the FPF. The residual water from tilapia intensive farming can provide sufficient nutrients for the production of lettuce, making the supplementary fertilization with commercial products unnecessary. Thus, the FPF presents the most suitable conditions to be used as substrate in aquaponics system with recirculation of the residual water from the intensive tilapia farming.

Host suitability of weeds and forage species to root-knot nematode meloidogyne graminicola as a funcion of irrigation management

The irrigated rice production can be limited by various phytopathogenic agents, including root-knot nematodes (Meloidogyne spp.). Thus, the aim of this research was to check the host suitability of plant species most often found off-season and during rice cultivation, to root-knot nematode Meloidogyne graminicola, under two irrigation managements. Two experiments were conducted in a completely randomized design. In the first experiment seven plant species that occur in an area of rice cultivation, in fallow, off-season were evaluated. For the second experiment nine weed species infesting the irrigated rice culture were tested in rainfed and flooding conditions. The sixteen species, kept individually in pots with sterilized substrate, were inoculated with 5,000 eggs and second stage juveniles (J2) of nematode. BRS 410 IRGA rice plants inoculated with M.graminicola were used as control. Two months after inoculation, the root system of each plant was evaluated for number of galls and nematode reproduction factor. It was verified that the species of off-season of rice cultivation Sida rhombifolia, Raphanus raphanistrum, Spergula arvensis, Lotus corniculatus and Trifolium repens, and, during the cycle of rice cultivation, Aeschynomene denticulata, Leersia hexandra, are immune to nematode. The plant species off-season, Avena strigosa and Lolium multiflorum and of cultivation, Alternanthera philoxeroides, red rice, Echinochloa crusgalli, Cyperus difformis, Cyperus esculentus, Cyperus iria and Fimbristylis miliacea would behave as hosts of M.graminicola, mostly under rainfed conditions.