Perennial alley cropping contributes to decrease soil CO2 and N2O emissions and increase soil carbon sequestration in a Mediterranean almond orchard.

The implementation of alley cropping in orchards can be a sustainable strategy to increase farm productivity by crop diversification and contribute to climate change mitigation. In this research, we evaluated the short-term effect of alley cropping with reduced tillage on soil CO2 and N2O emissions and soil total organic carbon (TOC) in an almond orchard under Mediterranean rainfed conditions. We compared an almond monoculture with tillage in all plot surface (MC) with almond crop with reduced tillage and growth of Capparis spinosa (D1) and almond crop with reduced tillage and growth of Thymus hyemalis (D2). For two years, soil CO2 and N2O were measured, with soil sampling at the start and end of the experimental period. Results showed that CO2 emission rates followed the soil temperature pattern, while N2O emissions were not correlated with temperature nor moisture. Soil CO2 emissions were significantly higher in MC (87 mg m-2 h-1), with no significant differences between D1 and D2 (69 mg m-2 h-1). Some peaks in CO2 effluxes were observed after tillage operations during warm days. Soil N2O emission rates were not significantly different among treatments. Cumulative CO2 and CO2 equivalent (CO2e) emissions were significantly highest in MC. When CO2e emissions were expressed on a crop production basis, D2 showed the significantly lowest values (5080 g kg-1) compared to D1 (50,419 g kg-1) and MC (87,836 g kg-1), owing to the high thyme yield, additional to the almond yield. No production was obtained for C. spinosa, since at least two more years are required. TOC did not change with time in MC neither D1, but it significantly increased in D2 from 3.85 g kg-1 in 2019 to 4.62 g kg-1 in 2021. Thus, alley cropping can contribute to increase the agroecosystem productivity and reduce CO2 emissions. However, it is necessary to grow evergreen alley crops such as thyme to obtain short-term increases in soil organic matter. Thus, to estimate increases in TOC with alley cropping, the plantation density and the period required by the crop to cover most of the surface are essential factors at planning the cropping strategy.

Estimation of Ecological and Human Health Risks Posed by Heavy Metals in Street Dust of Madrid City (Spain).

In this work, sampling was carried out in the urban area of Madrid to analyze the content of total heavy metals (Zn, Pb, Cu, Cr, Ni, and Cd) in the street dust. Contamination was evaluated using various indices, such as the Contamination Factor (CF), Enrichment Factor (EF), Geo-accumulation Index (Igeo), Potential Ecological Risk Index (RI), Pollution Load Index (PLI), the Human Health Index Hazard Index (HI), and Cancer Risk (CR). Pollution indices were related to traffic density and color. Traffic density was the factor that most influenced the values of the pollution indexes, but no significant differences were found with the color of street dust. The concentration of heavy metals in the urban dust of Madrid had the following sequence: Zn (895) > Cu (411) > Pb (290) > Cr (100) > Ni (42) > Cd (1.25 mg kg−1). The pollution levels were high or very high in Pb, Zn, and Cd regarding the environmental pollution indexes. Ingestion was the main route of exposure to heavy metals contained in street dust. The CR for adults and children is less than 1 × 10−6, which means that there is no risk for the population. However, the HI was 10 times higher in children than in adults.

Increased diversity of arbuscular mycorrhizal fungi in a long-term field experiment via application of organic amendments to a semiarid degraded soil.

In this study, we tested whether communities of arbuscular mycorrhizal (AM) fungi associated with roots of plant species forming vegetative cover as well as some soil parameters (amounts of phosphatase and glomalin-related soil protein, microbial biomass C and N concentrations, amount of P available, and aggregate stability) were affected by different amounts (control, 6.5 kg m(-2), 13.0 kg m(-2), 19.5 kg m(-2), and 26.0 kg m(-2)) of an urban refuse (UR) 19 years after its application to a highly eroded, semiarid soil. The AM fungal small-subunit (SSU) rRNA genes were subjected to PCR, cloning, single-stranded conformation polymorphism analysis, sequencing, and phylogenetic analyses. One hundred sixteen SSU rRNA sequences were analyzed, and nine AM fungal types belonging to Glomus groups A and B were identified: three of them were present in all the plots that had received UR, and six appeared to be specific to certain amendment doses. The community of AM fungi was more diverse after the application of the different amounts of UR. The values of all the soil parameters analyzed increased proportionally with the dose of amendment applied. In conclusion, the application of organic wastes enhanced soil microbial activities and aggregation, and the AM fungal diversity increased, particularly when a moderate dose of UR (13.0 kg m(-2)) was applied.