IMPACTS OF SEWAGE SLUDGE APPLICATION ON SUGARCANE CROP AND ON ENVIRONMENT

Abstract

This field research aimed to evaluate the effects of sewage sludge (SS) application, complemented or not with NP, NK, and NPK fertilizers, on sugarcane crop nutrition and yield to characterize the SS nutrient supplying potential, and the possible environment impacts due to SS-contained heavy metals in an Arenic Abruptic Paleudult. The SS was applied at doses of 0, 20 and 40 t ha 1 (wet material, with 620 g kg-1 of water), and N, P and K, respectively, at doses of 34, 60 and 83 kg ha-1. The nutrients and heavy metals’ concentration were determined in samples of sugarcane +1 leaves and above ground (stalks plus leaves). Leaves were sampled at 146 days after planting (dap), and the above ground part, at cane harvesting. The SS was a fertilizer-like to sugarcane crop cultivated during 18 months, mostly for supplying adequate levels of Ca, P, S and Zn. As effects of this, there were increases on acid phosphatase activity, and on biomass and sugar yields, in linear function of SS doses. Within the nutrients supplied by SS, it was verified that P was not the unique responsible for increasing stark yield, due to higher photosynthetic rate, once the phosphatases’ secondary balance was altered by Cu, Zn and B metals, probably as enzymatic catalyst. There were increases in N, Ca, P, Mg, S, Fe, Cu, B and Zn exportations by above ground part with SS addition, which were consequence of higher contents of B, Ca, Cu, S and Zn in vegetable tissue and/or, the greater biomass yield. Comparing the amount of exported nutrients by the above ground part with those added to the soil by application of 40 t ha 1 of SS, the inputs were positive, except for B and K, which were negative.