Long-term agro-management strategies shape soil bacterial community structure in dryland wheat systems.

Soil microbes play a crucial role in soil organic matter decomposition and nutrient cycling and are influenced by management practices. Therefore, quantifying the impacts of various agricultural management practices on soil microbiomes and their activity is crucial for making informed management decisions. This study aimed to assess the impact of various management systems on soil bacterial abundance and diversity, soil enzyme activities and carbon mineralization potential in wheat-based systems. To accomplish this, soil samples from 0 to 15 cm depth were collected from ongoing long-term field trials in eastern Oregon region under wheat (Triticum aestivum L.)-fallow (WF), WF with different tillage (WT), wheat-pea (Pisum sativum L.) (WP), WF under different crop residue management (CR) and natural undisturbed/unmanaged grassland pasture (GP). These trials consisted of an array of treatments like tillage intensities, nitrogen rates, organic amendments, and seasonal residue burning. This study was a part of the Soil Health Institute's North American Project to Evaluate Soil Health measurements (NAPESHM). Bacterial community structure was determined using amplicon sequencing of the V4 region of 16SrRNA genes and followed the protocols of the Earth Microbiome Project. In addition, extracellular enzyme activities, and carbon mineralization potential (1d-CO2) were measured. Among different trials, 1d-CO2 in WT, WP, and CR studies averaged 53%, 51% and 87% lower than GP systems, respectively. Enzyme activities were significantly greater in GP compared to the other managements and followed similar trend as respiration. We observed higher evenness in GP and higher richness in spring residue burning treatment of CR study. Our results indicated that species evenness is perhaps a better indicator of soil health in comparison to other indices in dryland wheat systems.

Comparative assessment of soil fertility across varying elevations.

Land elevation exerts a significant influence on soil fertility through affecting macro and micro climatic conditions and geomorphological processes. To evaluate the soil fertility at different elevation classes, namely 1600-2000, 2000-2400, 2400-2800, and > 2800 m, 350 surface soil samples (0-30 cm) were collected from the agricultural lands of northwestern Iran. Soil properties, including soil texture, calcium carbonate (CaCO3), pH, electrical conductivity (EC), organic matter (OM), and soil macronutrients (TN, P, and K) and micronutrients (Fe, Mn, Zn, and Cu), were measured. Finally, the interpretation and classification of the soil samples were made using the nutritional value index (NIV). The comparison of the NIV index based on elevation changes showed that the Gomez method classifies the soil properties in an optimal order as evidenced by its tendency towards the center of the data. However, the Common method is more consistent with the observed trend. After classifying the NIV index using the Common method, it was determined that CaCO3 and soil salinity are not the limiting factor for soil fertility in different elevation classes. However, in all elevations, high pH, low OM at elevations > 2800 m, total nitrogen (TN), available phosphorous (AP), and micronutrients deficiencies, except Zn at the elevation of 1600-2000 m, are the main limiting factors for soil fertility of agricultural lands. The results provide further insight into the elevation-based land evaluation and may supports grower's decision on nutrient management and crop selection strategies.

Distribution, source apportionment, and risk analysis of heavy metals in river sediments of the Urmia Lake basin.

The anthropogenic heavy metal dissemination in the natural environment through riverine sediments is a major ecological and public health concern around the world. This study gives insight into the source apportionment and potential ecological and health risks of heavy metals in river sediments of the Urmia Lake basin, a natural world heritage located in northwestern Iran. A comprehensive sediment sampling was conducted in seven major rivers feeding the basin during the summer and winter of 2021. Samples were analyzed for zinc (Zn), copper (Cu), cadmium (Cd), lead (Pb), and nickel (Ni) contents and a suite of chemical and physical properties. Subsequently, Pollution Index (PI), Pollution Load Index (PLI), Ecological Risk (ER), Hazard Quotients (HQ), Hazard Index (HI), and Carcinogenic Risk (CR) indices were determined. The mean concentration of heavy metals in all rivers' sediments exhibited the descending order of Ni > Zn > Pb > Cu > Cd during both summer and winter. Multivariate analysis suggested that Zn was primarily initiated from natural processes, Cd and Pb were affected by human activities, and Cu along Ni were derived from natural and anthropogenic factors. The PI unveiled that most sediment samples were unpolluted to slightly polluted by Zn, Cu, and Pb, and slightly to moderately polluted by Cd. PLI and ER indices demonstrated that the sediment poses non to moderate pollution and low to moderate ecological risk, respectively. Using a human health risk approach, we found that the HI values of all heavy metals and THI were less than one for children and adults implying non-carcinogenic risk in the analyzed sediments. Carcinogenic effects of Cd and Pb at all rivers sediments via ingestion, inhalation, and dermal contact were almost within tolerable risks (1 × 10-6 to 1 × 10-4) for children and adults. PI, PLI, ER, HQ, HI, and CR index values of sediment samples during the summer were higher than those during the winter. This is attributed to the greater heavy metal concentrations and the lower water flow during summer. Our results provide practical information for better management and control of heavy metal pollution in aquatic-sedimentary ecosystems.

When do cover crops reduce nitrate leaching? A global meta-analysis.

The global increases in the surface and groundwater nitrate (NO3 - ) concentrations due to synthetic fertilizer input have emerged as major sustainability threats to terrestrial and aquatic ecosystems. Cover crops can reportedly reduce nitrate leaching from croplands. However, the underlying mechanisms and the effectiveness of cover crops in reducing nitrate leaching across species, soil types, agronomic management, and climates remain elusive. We conducted a global meta-analysis to evaluate the effects of cover crops on nitrate leaching and water drainage. A random-effects analysis was established to investigate seven moderating variables in 41 articles. Results showed that globally, cover crops reduced nitrate leaching by 69% compared with fallow while demonstrating no effect on water drainage. Overall, cover crops from Brassicaceae and Poaceae families showed the greatest effect with 75% and 52% reduction in nitrate leaching, respectively. Cover cropping on Ultisols, Histosols, and Inceptisols resulted in the greatest reduction in nitrate leaching (77%, 78%, and 77%, respectively). Greater efficacy of cover crops at reducing nitrate leaching was evident with increasing soil sand content. In general, cover crops appeared to perform better to reduce nitrate leaching in vegetable systems compared to field crops. Cover cropping on conventional tillage resulted in a 63% reduction in nitrate leaching compared with no-tillage (50%) and reduced tillage (38%) systems. The impact of cover crops on water drainage was nonsignificant which implies that nitrate leaching control by cover crops is unlikely exerted through reducing water drainage. This study brings further insight into the intrinsic factors affecting cover crop efficacy and management practices that enhance cover crop potential in reducing nitrate leaching from agricultural systems.

Urbanization influences the distribution, enrichment, and ecological health risk of heavy metals in croplands.

The contamination of urban soils with heavy elements due to the rapid development of urbanization and urban services has become a major environmental and human health challenge. This study provides insight into the urbanization controls on combined pollution severity and health risk potential of heavy metals in corn-cultivated urban versus non-urban soils. A multifaceted assessment was conducted using enrichment factor (EF), ecological risk (ER), bioconcentration factor (BCF), transmission factor (TF), hazard index (HI), and carcinogenic risk (CR). The results indicate a significant increase in the concentration of all metals in urban farmlands. When compared to the non-urban soils, EF implies a significant increase of all metals in the urban soil, downgrading this index from minimal enrichment (EF < 2) in the control soils to moderate enrichment (2 ≤ EF < 5) in the urban soils. Likewise, the average ER value showed an increase in the urban soils than in the control soils in the order of Fluvisols (66.6%) > Regosols (66.1%) > Cambisols (59.8%) > Calcisols (47%). The BCF and TF values for different elements decreased in the order of Cd (0.41-0.92) > Cu (0.1-0.23) > Zn (0.1-0.18) > Ni (0.01-0.03) > Pb (0.005-0.011) and Zn (0.75-0.94) > Cu (0.72-0.85) > Pb (0.09-0.63) > Cd (0.17-0.22) > Ni (0.01-0.21), respectively, which indicates that certain metals were not mobilized to the extent that they had been accumulated in the plant roots. The total carcinogenic risk was ranged from 5.88E-05 to 1.17E-04 for children and from 1.17E-04 to 2.30E-04 for adults, which implies a greater associated health risk for children.

Spatial and quantitative assessment of wind erosion from adjacent dunes with different surface cover ratios.

Direct measurements, models, and risk maps play significant roles in assessment and monitoring of wind erosion cases. Although active and passive traps allow researchers to measure point sediment transports directly, it is also possible to make geostatistical analysis of wind erosion with grid and random sampling at multiple points. Geostatistical models can be used in multi-sample eolian researches to improve model success and update model parameters. The present study was conducted for case-based geostatistical analysis of sediment transport rates (STRs) over two adjacent dunes (plot A and B) with different vegetation cover rates between 22 May and 15 June 2011. The plot A has a vegetative cover ratio of 30%, while the plot B has a vegetation cover ratio of 2% and sand content of the plots is 88%. Actual mass transports were measured with BEST sediment traps. A total of 19 BEST sediment trap assemblies were placed randomly over the plot A and 21 were placed over the plot B. A climate station was installed over the research site to record climate data throughout the experimental period. There were two wind erosion cases during the research period. U test indicated that differences in sediment transport rates of the plots for each case were significant (p < 0.00). Spatial analyses of STRs (kg m-1 h-1) also exhibited case-based differences. While nugget effect was observed in case 1 of the plot B, the other case in both plots were modeled with spherical model. Maximum likelihood distances in plot A and B were respectively identified as 61 m and 1 m in the first case and as 13 m and 30 m in the second case. Total mass transport was measured as 112 kg m-1 in plot A and as 2162 kg m-1 in plot B. Consequently, it was found that 30% vegetation cover reduced the total mass transport dramatically.