Desempenho de colunas experimentais de solo irrigadas com água superficial poluída e cultivadas com alface (Lactuca sativa L.).

Abstract

This research aimed the physical, chemical and microbiological characterization of (1) soils of Paraiba State before and after irrigation with polluted and non polluted water, (2) waters used in the irrigation before and after percolating the soil columns, and (3) lettuces (Lactuca saf/va, L.) grown in these different soils. Three experiments were conducted during January to August/98 using PVC columns and irrigated either with superficial polluted water (3) or water from Gampina Grande Water Supply System (3). Irrigation and percolated water were analyzed for temperature, pH, electrical conductivity, BODs, total solids and fractions, total phosphorous, soluble orthophosphate, ions, fecal conforms and fecal streptococci. Same of these parameters were also analyzed in soil and culture. The pH values for both irrigation water were slightly neutral to alkaline not affecting plant growth. Irrigation water with an electrical conductivity below < 2080 u.mho/cm can be used for the cultivation of lettuce. The concentration of calcium, magnesium and potassium were considered adequate for irrigation water but not for chloride and sodium, although no direct effects on lettuce growth were observed. The organic matter in the polluted irrigation water ranged from 8 to 15 mg/l being reduced in 85% after percolating the soil column. Fecal coliforms in the polluted water were well above the recommended WHO values of 1000 CFU/100ml for irrestricted irrigation and after percolating, became absent in 22% of the samples and less than 1000 CFU/100ml in 26% of the samples. In both experiments irrigation with polluted water increased soil concentration of nitrogen and its percentage of organic matter (Exp. I: from 0,74 to 1,2%; Exp. II: from 0,52 to 1%). The concentration of soluble phosphorous were high in Exp. I (57,37 mg/100g), since soils were previously fertilized with animal manure, compared to those values of Exp. II (6,73 mg/100g). Soil initial electrical conductivity ranged from 200 jj.mho/cm (Exp. I) to 160 |amho/cm (Exp. II) and did not showed significant alteration at the end of the experiments indicating small risks of salinization. The concentration of fecal coliforms in the lettuces irrigated with polluted water ranged from 3,1x104 MPN/100g (Exp. I) to 1,9x103 MPN/100g (Exp. Ila) and for E. coii those figures varied from 8,7x102 MPN/100g (Exp. I) to 4,7x102 MPN/100g (Exp. Ila), showing the presence of health risks to those may consume those products without an adequate care.