Impactos e modificações em agroecossistemas cultivados com milho e algodão irrigados com água residuária tratada.

Abstract

With the objective of evaluating the impacts and modifications in the edaphic medium and on two crops caused by irrigation with treated wastewater and by nitrogen chemical manuring, a research was developed in the Sewers Treatment Station belonging to the Company of Water and Sewers of Paraiba state (CAGEPA), in Campina Grande, Brazil. The crops were fodder hybrid corn, variety AG 1051, and herbaceous cotton, variety BRS 187 8H. For the Experiment I (corn), the randomized blocks design was used with a factorial of [(2x5) +2], in which the factors were two types of water irrigation (treated wastewater and provisioning), five residual doses of nitrogen chemical manuring (0, 60, 90, 120 and 180kgN/ha) and two absolute proofs (water of provisioning and treated wastewater). In the Experiment I I (cotton), the experimental design was the same, however there was nitrogen chemical manuring in the doses of 0, 80, 160, 240 and 320kgN/ha. Both experiments had four replications. For the corn crop, the growth variables (height and diameter of the stem, foliar area per plant, diameter, length and weight of a corn ear), the production variables (weigh of corn ears with and without straw, weight of the slough and of the grains) and the microbiologic contamination of the corn grains were analysed. For the soil, physical, chemical (macro and micro nutrients), heavy metals and microbiology (total coliformes, fecal coliformes and Escherichia coli) analyses were made. For cotton crop, all soil analyses accomplished in the Experiment I were also performed for the Experiment I I , and for the plant, growth, production and fibers analyses. According to the results of the statistical analyses, it was concluded that both crops responded satisfactorily to irrigation with treated wastewater, having all growth and production variables responded better to irrigation with that kind of water than with water of provisioning. The corn obtained a production of 3812,5kg of grains/ha, while the production of cotton in pit was 3310kg/ha, overcoming in 116% the average of the brazilian Northeast, which is 1528kg/ha. The treated wastewater influenced the soil chemical elements in both experiments, having by the end of the Experiment I I increase of all micro nutrients and heavy metals in the soil. The levels of soil contamination by fecal coliformes and Escherichia coli fell at the end of the Experiment I , and even much more at the end of the Experiment II. The corn grains suffered contamination by total coliformes and fecal coliformes.