Tannery Sludge Applied in High Doses in Elephant Grass as an Alternative Fertilization

Tannery sludge has great potential for use in agriculture, however it is a potentially toxic waste, and it is necessary to establish the ideal dose for each crop. The objective of this study was to evaluate the influence of fertilization with liquid tannery sludge on growth, chlorophyll a fluorescence and gas exchange of Pennisetum purpureum in two production cycles. A 2 x 6 + 1 split plot scheme was used, where the first factor was composed of two productive cycles, the second factor different fertilizations doses: 0, 30, 70, 110, 150, 190 t ha(-1) of liquid tannery sludge and an additional treatment with nitrogen, phosphorus and potassium control. Plant height, number of leaves and tillers, canopy and stem diameter, leaf area, dry matter, chlorophyll index (SPAD), chlorophyll a fluorescence and gas exchange were evaluated. The highest production of total dry matter was observed in the second production cycle. The range between 72-100 t ha(-1) of liquid tannery sludge showed the greatest gains in growth and production of elephant grass. At doses above 150 t ha(-1) of liquid tannery sludge, the photochemical apparatus begins to show possible damage to the photosystem II (PSII) and reductions in gas exchange.