Factors that affect physicochemical and acid-base properties of compost and vermicompost and its potential use as a soil amendment

Composting and vermicomposting have attracted attention in relation to both waste management and the potential to produce organic amendments that could improve soil quality. The main differences between compost depend on the feedstock, the production process, and the degree of maturity. In the present study, samples of compost of different origin (food and green waste, livestock waste, algae waste, urban waste or sewage sludge) or subjected to different composting methods (traditional or using earthworms) were collected for analysis. Additionally, samples collected at various stages of the composting process were compared (raw material, 15 and 30 days of composting, and final compost). Different analysis and techniques were used to establish the chemical composition, physicochemical and acid-base properties of compost samples and the organic matter extracts. The correlations obtained (between the abundance of acid groups in different extracts of the compost or between the cation exchange capacity and the C/N atomic ratio) would allow for predicting the compost behaviour based on certain characteristics, and a reduction in the number of parameters determined experimentally, thus facilitating comparisons between different compost. In addition, the potential value of the compost as amendment was tested with a Haplic Cambisol from a mining area. The application of compost increased the pH, the organic matter and nutrient content, and promoted seed germination and root growth.This work was financially supported by the Interreg VA SpainPortugal Programme (EU) through the project Res2ValHum (0366_RES2VALHUM_1_P). R.L, J.A and S.F. are members of the CRETUS Institute (CRETUS, AGRUP 2015/02, ref. 2018-PG10) and were also supported by the Group of Excellence GI-1245 financed by the Xunta de Galicia (ED431C 2018/12). A.C. Silva acknowledges receipt of a PhD grant (UMINHO/BD/40/2016) financed by the Operational Program Norte 2020 (through the Project NORTE-08-5369-FSE-000033). LIPOR and other companies are also acknowledged for the supply of the compost samples. The authors thank M. Santiso, F Casas, J. Maceira, M. Orge and D. Fiuza for their assistance in characterizing the compost and soil samples. Finally, the authors would like to thank the feedback and comments of two anonymous reviewers