Sewage sludge as a pedotechnomaterial for the recovery of soils compacted by heavy machinery on Eucalyptus commercial plantation

Abstract

Commercial forestry activities featuring heavy machinery and intensive traffic represent one of the most common degradation processes in infertile Tropical soils. This research aimed to evaluate the potential of sewage sludge (SS) as pedotechnomaterial (PTM) for soil recovery in strongly degraded Entisols with a human-induced, highly compacted densic horizon (Ad). The area was used as a lumber deposit and for related forestry activities for more than ten consecutive years. Soil recovery activities consisted of: i) SS increasing dose applications (2.5, 5.0, 10.0, 15.0, and 20.0 Mg ha−1) in the surface mineral horizon, vs a control; and, ii) pioneer (Pn), secondary (Sc), and climax (Cx) native species plantation. Pioneer, Sc, and Cx were characterized by an increasing H and D trend as time went by, with Pn (H and D) > Sc > Cx. After three years, the highest SS dose (20 Mg ha−1) provided the best performance in most investigated species. Soil treated with the highest SS dose showed increased SOM, total P, CEC, exchangeable Ca, total Fe, Mn, Cu, and Zn contents after 36 months. No soil nutrient deficiency, potentially toxic elements (PTE) soil pollution, or related hazards were observed. The principal factor analysis showed that SS positively effects soil-plant feedbacks and related behavior. Canonical correspondence analysis explained how soil physical-chemical parameters influenced the whole plant ecological succession over time: i) during the early stage of development, Pn and Sc species were mainly affected by soil pH (SS buffering effect); ii) after one year, Ca, Mn, and CEC strongly influenced D development of mainly Sc species, thus further developing the whole soil-plant system; iii) at the end of the experiment, SOM and several soil macro- and micronutrients greatly influenced more demanding Cx species. For the first time, this research demonstrated the SS efficiency as PTM in strongly degraded Tropical soils; a PTM strongly favoring soil and forest restoration.