Effects of Curing Time on Physical and Chemical Properties of Composted Sewage Sludge Bind on the Growth of Selected Bedding Plants

Raw sewage sludge treated with lime and ferric chloride was composted by the Beltsville Aerated Pile Method, screened and piled outdoors (cured) for 4, 6, 8, or 10 months. As curing time increased there was a decrease in CO₂ and temperature, and an increase in O₂ within the piles. The NH₄ concentrations and electrical conductivity (EC) of the compost decreased while pH, NO₃ + NO₂, and extractable P increased with time. Curing time did not influence extractable K while bulk density (BD) and particle size distribution (PSD) exhibited only moderate changes. Marketable seedlings of Impatiens hybrida ‘Super Elfin Scarlet’ and Tagetes patula L. ‘Yellow Boy’ were produced in peat:vermiculite (v/v) amended with 10 or 20% compost, regardless of compost curing time. Seedlings of Coleus x hybridus Voss. ‘Saber Golden’ were stunted and unmarketable in all compost amended media. Increasing compost curing time decreased EC, pH, and extractable N and K of the media at transplant time, and resulted in increased dry weight of I. hybrida and T. patula. Increasing compost concentrations in the media decreased plant top dry weight and visual ratings, and increased EC, pH, and NH₄, NO₃ + NO₂, and extractable N, P, and K.