Fertirrigação com efluente doméstico tratado no cultivo de gérbera com e sem suplementação mineral.

Abstract

The available information concerning the effects of the application of treated wastewaters in irrigation is insufficient keeping in view the production or quality of cut flowers or in systems of agricultural production which evaluate the comparative sustainability in different forms of cultivation and types of soils. The aim of this research was to evaluate the technical viability of fertigation with treated domestic effluents in the cultivation of gerbera at Teresina, PI, due to the limitation of the water resources and the pollution created in the urban and rural areas. The study was conducted over a period of 120 days from July to October 2007 at Embrapa Meio-Norte, Teresina, State of Piauí, Brazil, in a greenhouse with a 50 % shadow screen, using treated sewer from the Sewer Treatment Station of the Companhia de Água e Esgotos do Piauí S.A. A completely randomized experimental design, with five treatments and five replications was used. The treatments differed in volume of wastewater and the application of chemical fertilizers (urea and potassium chloride). The treatments studied were: TI – 100 % chemical fertilization; TII – 25 % chemical fertilization and 75 % Treated effluent; TIII – 50 % chemical fertilization and 50 % treated effluent; TIV – 75 % chemical fertilization and 25 % treated effluent; and TV – 100 % treated effluent. The results obtained in Treatment IV met the commercial requirements for number of flowers, however in terms of the quality, Treatment II produced flowers in July and August with longer stem length achieving IBRAFLOR extra standards. In the final months (September and October) no treatment achieved this limit, due to the high temperature and low humidity which provoked losses in growth, appearance and quality. The quality of water and applied effluent did not restrict its use in irrigation. The electrical conductivity of the effluent increased in September and October to 0.82 and 0.90 dS m-1, respectively, presenting little to moderate restrictions in its use in irrigation. It may be concluded that the leaf contents of macronutrients (N, P, Ca and Mg) and micronutrients (Zn, Cu, Mn, Fe and B) were not affected under the domestic effluent treatments with and without mineral supplementation in the experiment. The analysis of the soil material before and after the application of the treatments revealed a small increase in some soil attributes at the end of the trial particularly in case of treatment with the application of 100 % treated effluent (pH increased from 5.24 to 5.76, Ca2+ from 1.71 to 3.14 cmolc dm-3 and Mg2+ from 1.03 to 1.44 cmolc dm-3, and the sum of extracted cations from 3.11 to 4.92 cmolc dm-3). The highest concentrations of N and C were observed in the soils irrigated with 100% treated effluent, possibly due to fast mineralization of organic matter, reducing their contents under this treatment. These alterations in the chemical attributes did not provoke harmful effects in gerbera crop. The use of the treated domestic effluent was satisfactory permitting the partial substitution of chemical fertilizers by the nutrients contained in the effluent constituting thereby an alternative for the flower growers.