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| Author(s): |
Bruno Fernando Faria Pereira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2010-02-22 |
| Examining board members: |
Adolpho Jose Melfi;
Cassio Hamilton Abreu Junior;
Otavio Antonio de Camargo;
Francisco de Assis Alves Mourão Filho;
Sandra Furlan Nogueira
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| Advisor: | Adolpho Jose Melfi |
| Abstract | |
Considering two different agroecosystems (Piracicaba, SP, Brazil and Okeechobee, FL, USA) cultivated with citrus, the objectives of the study were to evaluate: i) the concentration of nutrients, heavy metals in reclaimed wastewater (RWW) and its quality for the agricultural use; and ii) the effects of RWW irrigation on soil fertility and plant nutrition. At Piracicaba, SP, an experiment were carried out with three randomized blocks and five treatments. Four different RWW irrigation rates were applied over 21 months, in orange trees [Citrus sinensis (L.) Osb] on Citrus paradisi Macfad. x Poncirus trifoliata Raf], based on crop evapotranspiration (ETc): 100%, 125%, 150% and 200% of ETc as well as a treatment without irrigation (0%). At Okeechobee, FL, a survey study was carried out in a commercial citrus grove cultivated with grapefruit [(Citrus paradise Macf.) on (Citrus aurantium L.)]. At this site two citrus blocks were compared; one irrigated with RWW (11 years) and the other with well water. The RWW used in both studies displayed satisfactory quality for the agricultural use (FAO, 1992). The first agroecosystem had negative correlation between RWW irrigation rates and active acidity, potential acidity, aluminum saturation, exchangeable K and available Pb. Whereas positive correlations were found for S, B, Cu and Na in soil with RWW rates. Comparing the irrigation rate of 100% of ETc with the control plot (0%), increasing contents of N, 15N, S, B, and decreasing contents of P, K, Mn, Al and Cr were observed in the leaf tissue. Lower concentrations of these elements were associated with the over irrigation rates (> 100% of ETc). The greatest effect of the irrigation rates on plants height was found between 93 and 107% of ETc. At the second agroecosystem, increasing concentration of NH4 +, NO3 -, Mg, S, B, Cl, Co, Cu, Fe, Mn, Mo, Ni and Zn in soil were found after 11 years of RWW irrigation. In leaf tissue also increasing concentrations of Ca, Mg, B, Fe, Cu, Mn, Ni and Zn were determined. Concentration of Cd, Co, Mo and Pb were below the detection limit of detection in the leaf tissue. The effects of the RWW irrigation are pronounced after long term application, and can partially supply some nutrients from the fertilization program. Even after long term RWW irrigation, the risks of soil salinization and heavy metals accumulation can be considered as low. The results highlight that besides an alternative waster source, RWW can provide benefits on soil fertility and citrus nutrition. (AU) | |