Sour passion fruit (Passiflora edulis Sims) seedlings in response to sewage sludge-derived biochar and compost

Waste resulting from domestic sewage treatment, i.e., sewage sludge (SS), could potentially be used as fertilizer. To make its use as vegetable fertilizer safe, SS pollutants can be eliminated by pyrolysis. The solid product resulting from SS pyrolysis is called biochar and can be used in vegetable production. There are still doubts about the effect of replacing conventional compost with biochar. For this reason, this study evaluated the effects of sewage sludge-derived biochar (SSB) and a compost (COM), blended with growth substrate at different concentrations to produce seedlings of sour passion fruit. Nine treatments were evaluated: 1) Control, without SSB or COM application; 2) fertilization (v/v) with SSB (2.5%); 3) SSB (5.0%); 4) SSB (7.5%); 5) SSB (10.0%); 6) COM (2.5%); 7) COM (5.0%); 8) COM (7.5%); 9) COM (10.0%). The following seedling traits were evaluated: shoot length, stem diameter, number of leaves, fresh shoot and root weight, root length, dry shoot and root weight and the Dickson Quality Index (DQI) that determines the seedling quality. Photosynthetic pigments were also evaluated and leaf contents of a, b and total chlorophyll and carotenoids were calculated. It was found that the physical characteristics of the seedlings and DQI improved in response to the application of COM (10.0%) in comparison with the other treatments and the control. In addition, the biochemical characteristics were improved by SSB (2.5%) application, over the other treatments. Separately, SSB and COM increased seedling quality and the combined effects of these inputs needs to be studied in future works.