Patrice Cannavo

Urban green infrastructure (UGI) often relies on constructed soils, yet it remains unclear how Technosol composition and irrigation regulate soil organic carbon (SOC) fractions and microbial functioning under semi‐arid conditions. An 18‐month mesocosm experiment in Central Chile compared four Technosol mixtures differing in excavated subsoil (ExS) content under two irrigation regimes with lavender plantations. SOC fractions (POM and MAOM), microbial respiration (BR, SIR), substrate‐use patterns (CLPP), qCO ₂ and enzymatic activities were assessed over time. SOC and MAOM were progressively higher with increasing ExS content (SOC: ~19 g kg ⁻¹ in sand‐rich mixtures C and A to 31.9 ± 4.9 g kg ⁻¹ in ExS mixture TE; MAOM: ~2.9% to 5.64% ± 0.96%), indicating that mineral matrix composition controlled early organo‐mineral carbon allocation under equal compost inputs. Over time, MAOM increased while POM declined, reflecting a redistribution toward mineral‐associated pools. Microbial respiration was consistently higher in ExS‐rich mixtures and intensified over time. Similarly, SIR increased over time (27.4 ± 8.3 to 50.1 ± 22.4 μg CO ₂ –C g ⁻¹ h ⁻¹ ), whereas qCO ₂ declined over time. Substrate‐use patterns in ExS mixtures shifted toward greater utilization of carboxylic acids, while enzymatic activities showed limited responsiveness, except for urease. Technosol composition was the primary driver of early SOC fraction dynamics and microbial functioning, whereas irrigation within realistic ranges played a secondary role. Selecting an ExS‐rich mineral matrix represents a key design strategy to promote early organo‐mineral carbon association and sustain microbial functioning in semi‐arid UGI soils.

Lawns, which can represent up to 50–70% of urban green spaces, provide key ecosystem services. However, their greenhouse gas (GHG) emissions depend strongly on management practices. Conventional practices—such as mineral fertilization and irrigation—increase soil nitrous oxide (N ₂ O) emissions and contribute to the carbon footprint of lawns. In contrast, alternative approaches—such as organic fertilization, reduced mowing frequency, and recycling of grass clippings and tree litter on soil surface—may improve carbon storage and reduce GHG emissions. However, litter decomposition may also lead to N ₂ O emissions. This study aimed to assess the impact of 11 conventional and alternative lawn management practices, on carbon dioxide (CO ₂ ) and N ₂ O emissions, with a particular focus on comparing the effects of mineral and organic fertilization. GHG fluxes were measured in spring, summer, and autumn, and analyzed in relation to soil temperature, moisture and mineral nitrogen concentrations. Organic fertilization induced 8.1 times less cumulative N ₂ O emissions (2–5 mg N m ^− 2 ) than mineral fertilization (34–70 mg N m ^− 2 ). Recycling of grass clippings and tree litter on soil surface did not increase CO ₂ and N ₂ O emissions. Lawns mowed once a year emitted 1.5 times less CO ₂ (752 mg CO ₂ m ^− 2 h ^− 1 ) than conventional lawns mowed weekly and receiving mineral fertilizer (1147 mg CO ₂ m ^− 2 h ^− 1 ). The results suggest that mineral fertilization should be replaced by organic alternatives to reduce N ₂ O emissions, and that spring applications should be delayed or avoided to enhance N use efficiency. Furthermore, reducing mowing frequency and recycling litter on lawns appear to be sustainable alternatives, as they have a low potential for GHG emissions while also supporting soil fertility, carbon storage, water cycling, and biodiversity.

Aim: Composts made from food waste will soon become more widespread on the market thanks to the upcoming enforcement of the legal obligation to sort biowaste. Our experiment aims at improving knowledge on the short‐term effects of these composts on soils’ physicochemical properties and vegetable crops.Methods: Three composts with contrasting characteristics were tested: a 100% v/v green waste compost (C1), and two composts composed of 50% v/v food waste and 50% v/v green waste, one prepared directly on the soil (C2) and the other from a competing producer who have the French NFU 44‐051 (AFNOR NF U 44‐051, 2006) certification for an organic amendment (C3). They were applied at a rate of 100 t ha⁻¹ (dry matter) on two cropped soils with contrasting textures. Soil‐and‐compost mixes and compost‐free soil were planted with lettuce, radish, and potato.Results: Seventy‐four days after planting, composts improved some soil physicochemical properties. The compost‐amended soils had better saturated hydraulic conductivity (K_s, 1 10⁻³–2.5 10⁻³ cm s⁻¹) than the compost‐free soil (0.5 10⁻³ cm s⁻¹), and water‐stable aggregates were higher than the initial value in C3 soil, equal to it in C2 soil, and lower in C1 soil. pH, total nitrogen, and organic carbon increased in all compost‐amended soils. Food waste compost stimulated crop production. The yields (dry matter) of all three crops were two to three times higher in the two soils amended with food waste compost compared to unamended soil, whereas they decreased almost two times in the soil amended with green waste compost due to nitrogen immobilization. Trace metals (particularly Pb and Cd) added by the composts, although present in edible parts of the plants, did not exceed the European rules for trace metals.Conclusion: Thus, food waste composts have positive effects on soils and vegetable crops, and the higher their organic matter content, the higher these positive effects.

ISHS XXXI International Horticultural Congress (IHC2022): International Symposium on Plant Nutrition, Fertilization, Soil Management Apple trees enhance soil organic matter and soil microbial activity in a garden-orchard system

Green roofs are very popular and their individual surface area is constantly growing. Considering that the organo-mineral materials used in planting growing media (GM) are often non-renewable resources, the search for alternative materials from waste recycling is a challenge. Among these, recycled polyurethane (PU) foams are light and porous. The objective of this study was to evaluate the potential agronomic valorisation of PU foams for extensive green roofs. Three GM based on compost, PU foam and topsoil were developed and tested in situ for 18 months along with four plant species in containers containing 15 cm of GM. The agronomic properties of the GM and their contaminant contents were evaluated, as well as the plant aerial and root biomasses and trace element levels. The main results of this work are that GM are suitable for plant growth. Compost ratio effect resulted in a lower pH and higher exchangeable cations in GM1, whereas topsoil proportion effect mainly decreased macroporosity and increased nutrient contents. Furthermore, due to the high trace element load in the compost, hyperaccumulator plants such as Hypericum calycinum and Stipa tenuissima should be preferred. Ecotoxicological analyses will be carried out to validate the absence of risk of PU foam contaminants being released in the environment before proposing these types of GM to green roof developers.