Mulching is a widely employed soil management practice. The mulches used have variable effects on the soil properties and plant growth. In China, mulches are used to cover bare soil at a few places in landscapes, where most of the soil is uncovered, especially in tree pits. As to improve our understanding on the effect of various mulches on soil properties and tree growth after two years of the treatment justifying its implication in soil fertility and tree growth. A comparison study was conducted to determine the effects of inorganic (cobblestone—CB; water permeable brick—WPB), organic (pine bark—PB; green waste compost—GWC), and living (turf grass—TG) mulches on soil physical and chemical properties at three different depths (0–10 cm, 10–20 cm, and 20–40cm), and on tree growth (Sophora japonica) in urban tree pits. Soil moisture was measured once a month in 2015.The soil samples were collected from the tree pits two years after mulching and used to evaluate the physical and chemical properties. Further, trunk diameter and tree height were determined once a year. During the most months, all types of mulches significantly affected the moisture content of the soil at all the depths analyzed. In July and August, however, the moisture content of PB and TG treated soil decreased when compared with that of unmulched bare soil. Two years after mulching, the bulk density of the soil treated with PB, GWC, and TG was significantly affected at10–20 cm, with GWC exhibiting a relatively better effect. The treatments with PB, GWC, and TG also improved the total porosity, macroporosity, and microporosity of the soil at lower depths. Further, WPB worsened the bulk density and porosity of the soil, elevating the pH at lower depths. The organic matter, total N, mineral N, available P, and available K contents of the soil at lower depths increased when mulched with organic material. Turf grass significantly increased only the total N and available K at 0–10 and 10–20 cm. There was no significant difference in the soil properties among the treatments at 20–40 cm. Furthermore, the trunk diameter and tree height were not affected by the mulches two years after mulching. In conclusion, organic mulches especially GWC, not only increased soil fertility significantly but improved soil physical characters (0–10 cm depth) comparing to other mulches, are suitable to cover bare soil in urban tree pits.

Resource utilization of urban green waste compost for soil improvement in afforested land is an important way of digesting urban green waste. In this study, artificial Sophora japonica Linn. Woodland in the Beijing plain, where the million mu (66,700 ha) afforestation project was carried out, was taken as an experimental area to investigate the influences of urban green waste composting on soil improvement and soil microorganisms. Application amounts of green waste composts for each tree were as follows: CK treatment: no application of fertilizer; T1 treatment: 5 kg/each tree; T2 treatment: 10 kg/each tree; T3 treatment: 15 kg/each tree. Results showed that the application of green waste had a significant effect on soil improvement, such as improving of organic matter, available phosphorus, and available potassium content (p < 0.05). The high-level application amount (T3 treatment) had a greater effect on soil improvement. Compared with the control treatment (CK), soil pH in T3 treatment decreased to 7.28–7.45, Soil organic matter contents reached more than 35 g·kg⁻¹, and soil total nitrogen, soil available phosphorus, and soil available potassium increased by 25–28%, 200–400%, and 80–177%, respectively. Soil carbon–nitrogen ratio has increasing to 15.61–24.38 in the three treatments, which would not obviously slow down the decomposition of organic matter by microorganisms in the soil. After the application of green waste compost, the soil microbial structure was changed. From the operational taxonomic unit (OTU) level, bacterial abundance increased by 12–13%, but the change in bacterial diversity was not significant. The influences of pH and contents of organic matter content, available phosphorus, and rapidly available potassium on the bacterial community were greater. This study will provide the necessary scientific basis for the application of green waste compost in the improvement of soil on afforested land in the Beijing plain.

Urban forest soil is often disturbed by frequent human activity. Organic mulching is effective for improving soil quality; however, the effects of organic mulching on soil bacterial communities in urban forests are still largely unexplored. This study evaluated how organic mulching changed the urban forest soil bacterial community through an incubation experiment. Four treatments were applied: (1) no organic mulch (CK); (2) wood chips alone (5 g, Mw); (3) wood compost alone (5 g, Mc); and (4) wood chips + wood compost (This mulch was divided into two layers, i.e., the upper layer of wood chips (2.5 g) and the lower layer wood compost (2.5 g, Mw+c).) We found significant differences in the soil physicochemical properties under organic mulching after incubation. Overall, organic mulching can alter soil bacterial community structure. Soil alkali-hydrolyzable nitrogen, soil organic carbon, soil total nitrogen, and carbon-nitrogen ratio were the main factors affecting soil microbial community structures. Soil bacterial groups under organic mulching treatments mainly acted on the C and N cycling of functional pathways in soil. This study suggests that organic mulching could maintain the development of soil bacteria, which establishes a theoretical foundation for enhancing the microbiological environment of urban forest soils.

Soil dust is one of the sources of PM2.5, and most soil dust is derived from bare soil. Our laboratory experiment was conducted to explore the effects of different mulching materials, including cobblestones (CS), green waste (GW), pine bark (PB), and organic mulching mats (OMM) on reducing the generation of soil dust from bare soil by different wind speeds near the ground (2 m/s, 4 m/s, 7 m/s, 9 m/s, and 12 m/s). The results showed that all 4 mulching materials reduced the generation of atmospheric soil dust. Both GW and OMM had the best effect at reducing dust generation when the wind speed near the ground 4 m/s. The mulching materials GW and PB could be completely blown away when the wind speed near the ground reached 7 m/s and 9 m/s, respectively. It appears that OMM is the best mulching material for covering bare soil in Beijing.

Objective: Forestry management produces abundant residues including wood chips, fallen leaves and bark. Reusing them as urban organic mulches improves soil quality, mitigates soil erosion and optimizes urban green space ecology. This study analyzed the water-holding characteristics of four typical forestry residues to guide urban mulch selection. Methods: Soaking lab tests were conducted on pine bark (PB), oak leaves (OLs), pine needles (PNs), and fir wood chips (FWCs) to monitor dynamic variations in water-holding capacity and absorption rate over soaking time, with data fitted by mathematical models. Results: All forestry residues exhibited considerable water-holding capacity, with OLs showing the highest water-retention performance (175.67 t/ha, 145.42%), effective interception capacity (119.83 t/ha) and interception rate (99.19%) among all tested materials, followed by FWCs. The water-holding capacity increased rapidly and then leveled off with prolonged soaking time, and this trend conformed to a logarithmic equation, expressed as Q = a·ln(t) + b. Water absorption peaked at 15 min before declining slowly until equilibrium, and this dynamic process was well fitted by a power function, expressed as V = k·tⁿ. Conclusions: Given their superior water-holding characteristics, OLs and FWCs are highly recommended as preferred organic mulches for urban soil applications.