Using waste products is a promising and sustainable alternative to conventional non-renewable peat and nutrient-rich renewable materials. Their products are gaining importance for closing the loop in the ornamental plant industry. Porous inorganic materials have recently become potential bulking agents (BA) for sewage sludge (SS) owing to their high porosity, surface area, passivation capacity, high recycling potential, and potting soil components. The main purpose of the present work was to investigate the feasibility of pumice (PU) and expanded perlite (EP) on composting parameters, nutrient bioavailability and suitability of SS to serve as an ornamental substrate. The addition of PU and EP at 50% (v/v) resulted in higher porosity, optimal initial moisture content, higher temperature rise (56.24 ± 0.13 °C, 56.21 ± 0.11 °C, respectively), and higher CO₂ evolution (39.41 ± 0.17%, 41.70 ± 0.22% daily peaks). Composting with inorganic BA at EP-50 and PU-50 mixtures was beneficial owing to high nitrogen content (3.82 and 3.70%, respectively) and readily bioavailable nutrients (270 mg kg⁻¹ phosphates and 1835 mg kg⁻¹ potassium). The use of PU and EP was found helpful in improving the slow-release nutrient properties of the compost. The overall results indicated that composting SS with PU and EP is a viable approach to achieve good composting properties and a good nutrient-providing profile if the compost is used as a component for potting soil components or garden soil amendments.

This study explores the production of bio-nutrients from bioactive compound-rich spent coffee grounds (SCG) and biochar (BC) through composting after inoculation with a biological agent and its impact on the growth performance of garden cress and spinach. The SCG was composted with six doses of BC (0, 5, 10, 15, 20, and 25%). The compost with 10% BC exhibited the best maturity, humification, and phytotoxicity index values of dissolved organic carbon (DOC), humification index (E4/E6), and germination index (GI). A metagenome analysis showed that compost starter enhanced the bacterial community’s relative abundance, richness, and diversity in SCG and BC treatments. This improvement included increased Patescibacteria, which can break down noxious phenolic compounds found in SCG and BC. The BC enriched the compost with phosphorus and potassium while preserving the nitrogen. In plant growth experiments, the total chlorophyll content in compost-treated garden cress and spinach was 2.47 and 4.88 mg g−1, respectively, which was significantly greater (p ≤ 0.05) than in unfertilized plants and similar to the plants treated with traditional fertilizer. Overall, the results show that the compost of SCG + BC was well-suited for promoting the growth of garden cress and spinach, providing adequate nutrients as a fertilizer for these leafy vegetables.

The most widely used growing media in the production of potted ornamental plants is peat. However, the studies for alternative solutions are being conducted due to the reasons such as restricted peat sources, high cost, destruction of natural environment due to peat production and variability in the quality of produced peat. In the relevant literature, there are two basic ideas on which the studies have focused on. The first one is the development of new growing media using organic-origin wastes, the second one is the preparation of the mixtures in which organic and inorganic materials are used as a component of growingmediums. In this study which was prepared in parallel with the relevant main ideas in the literature, the effects of perlite utilization on the physical properties of indigenous peat, and on those of the growing media obtained from hazelnut cinder, which is among agricultural organic materials in our country and has considerable potential to be the most important alternative of peat, were investigated. For this purpose, the physical properties of the growingmedias, prepared by mixing perlite with raw peat and hazelnut husk, at various ratios (10,15,20,25%), were investigated, and the results obtained were compared with sphagnum peat, and with desired properties for ideal growingmedias, in the literature. When the results obtained from the study were examined, it was seen that as well as the highest values were observed in the mixtures using 25% perlite, the perlite addition increased the porosity of raw peat by 68.25% and air capacity by 30.03%, and that the hazelnut husk decreased air capacity, higher than the ideal values, by 47.19%,thus approximating it its ideal value range. With increasing perlite ratio in the mixtures, the organic substance contents and water holding capacities of the growingmedias decreased as their pH values increased. However, in applications using 25% Perlite, the shrinkage rates of raw peat and hazelnut husk were found as 17.05% and 6.41% respectively, and the water resuction times of those were found as 1.52 and 1.21 minutes, respectively. Based on these results, it can be said that the most important contribution of perlite utilization for raw peat and hazelnut husk is to decrease shrinkage rates and water resuction times, and that this improvement will avail in preventing the damages that occur in plant roots due to drying and shrinking of the growing media, and in decreasing the irrigation frequency.