Composted Sewage Sludge as a Substrate for Commercial Seedlings of Peltophorum dubium (Spreng.) Taub.

Sewage sludge in natura is rich in nutrients, water, and organic matter and is essential for plant development. However, sewage sludge is diluted with water when composted, which could hamper plant growth. Therefore, supplementation with chemical fertilization may be necessary. This study evaluated the performance of composted sewage sludge (CSS) in producing Peltophorum dubium (Spreng.) Taub. seedlings with and without chemical fertilization via fertigation. The experiment was completely randomized in a 3 × 4 factorial scheme, with four fertigation (Ca(NO3)2(H2O)x: 0.87; (NH4)(H2PO4): 0.21; KCl: 0.47; (NH4)2SO4: 0.11; CH₄N₂O: 0.54; MgSO4: 0.52; Fe (13%): 0.03; B(OH)3: 6.00; CuSO4: 0.60; ZnSO4: 1.40; MnSO4: 6.00; Na2MoO4: 0.16 g L−1) doses: zero, standard, duplicate, and quadruplicate. In addition, three substrates were used: commercial substrate as the control, sewage sludge composted with sugarcane bagasse (LBC), and sewage sludge composted with Eucalyptus bark (LCE). The development of the seedlings was measured through the following variables: height, stem diameter, shoot/root ratio, leaf dry mass, root dry mass, total dry mass, green color index, the Dickson Quality Index, and the accumulation of nutrients in plant tissue. The seedlings produced with LCE that were subjected to the standard dose (1×) and the quadruplicate dose (4×) had the statistically highest mean values for most variables. Nevertheless, supplementation with chemical fertilization was necessary. Composted sewage sludge with eucalyptus bark, at the standard dosage, can be used for the commercial production of P. dubium seedlings, thus preventing the dangerous disposal of waste and strongly decreasing associated environmental hazards.