Effect of sewage sludge (biosolids) on nutrition, nutrients cycling and understory growth, in eucalyptus plantation

The contamination of water resources for wastewater is one of the main problems faced by the modem society, mainly in the great urban centers. The treatment of wastewater generates a residue, most of the time discarded in landfills, that could be used to increase the productivity of agricultural or forest plantations. The general aim of this research was to study the effect of the biosolids application, complemented or not with inorganic fertilizers, on the nutritional status, nutrients cycling and understory of a young plantation of Eucalyptus grandis Hill ex Maiden. The trial was stablished in the Experimental Station of Itatinga, linked to the Department of Forest Sciences, of ESALQ/USP. For nutritional monitoring, leaves of eucaliptus were collected too, two, four, six, eight, twelve and sixteen months after biossolids application for macro and micronutrients analysis. The study of nutrients cycling has been initiated seventeen months after the plantation, for occasion of the closing of the crowns, and thirteen months after biosolids application. Analysis of the understory was carried out by quantifying the aboveground biomass and nutrients concentrations, to the eight, sixteen and twenty months after application. The experiment is designed in randomized blocks, with 4 replicates and 9 treatments: control (tt), inorganic fertilize (ad), 5 t ha-1 of biosolids with K (5+K), 10 t ha-1 of biosolids with K (10+K), 10 t ha-1 of biosolids without K (10),10 t ha-1 of biosolids with K and P (10+KP), 15 t ha-1 of biosolids with K (15+K), 20 t ha-1 of biosolids with K (20+K) and 40 t ha-1 of biosolids with K (40+K). The biosolids altered, significantly, the nutritional status of the eucalyptus, except for Fe and Na. The plants that received the largest biosolids rate (40 t ha-1), showed that highest N, P, Ca, S concentrations and the smallest concentrations of Mn and Mg. The plants treated with the larger biosolids rate, deposited 136% more litter-fall than the control plants and 40% where the plants received inorganic fertilizer. The treatment "20 + K", that it received 20 t ha-1 of biosolids, showed highest medium amount of gramineas in the understory, however in just two blocks, what determined high variation around the mean and the not statistical significance. The biosolids application in a young plantation of E. grandis has improved the nutritional status of the plants and it has contributed to larger nutrients recycling in the ecosystem. The understory growth has not been homogenously affected. (AU)