Effects of Compaction on Soil Biota and Soil Biological Processes

Effects of Forest Harvesting Operations on the Recovery of Earthworms and Nematodes in the Hyrcanain Old-Growth Forest: Assessment, Mitigation, and Best Management Practice

The quality and performance of forest soil is closely related to the characteristics of the faunal community in the soil. Focusing on soil organisms can provide good indicators to choose the best soil restoration methods to improve the properties of degraded forest soils. Therefore, the present study aimed to evaluate the effects of the tree litter of different species on the recovery of soil organisms (earthworms and nematodes) from skid trails over a 20-year period after harvest operations. For this purpose, three skid trails with different ages after harvest operations (6, 10, and 20 years), considering three tree litter treatments (beech, beech–hornbeam, and mixed beech) and three traffic intensity classes (low, medium, and high), were identified. The combination of treatments was carried out in the forest with three replications, and a total of 18 sample plots of 0.5 m2 were harvested to measure earthworms and nematodes. The results showed that 20 years after harvest operations, the highest values of earthworm density (5.72 n m−2), earthworm biomass (97.18 mg m−2), and total nematodes (313.65 in 100 g of soil) were obtained in the mixed beech litter treatment compared to other litter treatments. With decreasing traffic intensity from high to low, the activity of soil organisms increased, and the highest values of earthworm density (5.46 n m−2), earthworm biomass (87.21 mg m−2), and soil nematodes (216.33 in 100 g soil) were associated with low traffic intensity. Additionally, in all three litter treatments and traffic intensities, the epigeic ecological species were more abundant than the anecic and endogeic species. Key soil variables including water content, porosity, available nutrients, pH, total organic C, and total N were significantly correlated with earthworm density and biomass and soil nematode population. Litter management and addition to compacted soil can support the functional dynamics and processes of the soil and maintenance of the abundances and activities of the soil fauna.

Limited resilience of the soil microbiome to mechanical compaction within four growing seasons of agricultural management

Soil compaction affects many soil functions, but we have little information on the resistance and resilience of soil microorganisms to this disturbance. Here, we present data on the response of soil microbial diversity to a single compaction event and its temporal evolution under different agricultural management systems during four growing seasons. Crop yield was reduced (up to -90%) in the first two seasons after compaction, but mostly recovered in subsequent seasons. Soil compaction increased soil bulk density (+15%), and decreased air permeability (-94%) and gas diffusion (-59%), and those properties did not fully recover within four growing seasons. Soil compaction induced cropping system-dependent shifts in microbial community structures with little resilience over the four growing seasons. Microbial taxa sensitive to soil compaction were detected in all major phyla. Overall, anaerobic prokaryotes and saprotrophic fungi increased in compacted soils, whereas aerobic prokaryotes and plant-associated fungi were mostly negatively affected. Most measured properties showed large spatial variability across the replicated blocks, demonstrating the dependence of compaction effects on initial conditions. This study demonstrates that soil compaction is a disturbance that can have long-lasting effects on soil properties and soil microorganisms, but those effects are not necessarily aligned with changes in crop yield.

Machine-Learning Classification of Soil Bulk Density in Salt Marsh Environments

Remotely sensed data from both in situ and satellite platforms in visible, near-infrared, and shortwave infrared (VNIR–SWIR, 400–2500 nm) regions have been widely used to characterize and model soil properties in a direct, cost-effective, and rapid manner at different scales. In this study, we assess the performance of machine-learning algorithms including random forest (RF), extreme gradient boosting machines (XGBoost), and support vector machines (SVM) to model salt marsh soil bulk density using multispectral remote-sensing data from the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) platform. To our knowledge, use of remote-sensing data for estimating salt marsh soil bulk density at the vegetation rooting zone has not been investigated before. Our study reveals that blue (band 1; 450–520 nm) and NIR (band 4; 770–900 nm) bands of Landsat-7 ETM+ ranked as the most important spectral features for bulk density prediction by XGBoost and RF, respectively. According to XGBoost, band 1 and band 4 had relative importance of around 41% and 39%, respectively. We tested two soil bulk density classes in order to differentiate salt marshes in terms of their capability to support vegetation that grows in either low (0.032 to 0.752 g/cm³) or high (0.752 g/cm³ to 1.893 g/cm³) bulk density areas. XGBoost produced a higher classification accuracy (88%) compared to RF (87%) and SVM (86%), although discrepancies in accuracy between these models were small (<2%). XGBoost correctly classified 178 out of 186 soil samples labeled as low bulk density and 37 out of 62 soil samples labeled as high bulk density. We conclude that remote-sensing-based machine-learning models can be a valuable tool for ecologists and engineers to map the soil bulk density in wetlands to select suitable sites for effective restoration and successful re-establishment practices.

Soil compaction effects on soil health and cropproductivity: an overview

Soil compaction causes substantial reduction in agriculture productivity and has always been of great distress for farmers. Intensive agriculture seems to be more crucial in causing compaction. High mechanical load, less crop diversification, intensive grazing, and irrigation methods lead to soil compaction. It is further exasperated when these factors are accompanied with low organic matter, animal trampling, engine vibrations, and tillage at high moisture contents. Soil compaction increases soil bulk density and soil strength, while decreases porosity, aggregate stability index, soil hydraulic conductivity, and nutrient availability, thus reduces soil health. Consequently, it lowers crop performance via stunted aboveground growth coupled with reduced root growth. This paper reviews the potential causes of compaction and its consequences that have been published in last two decades. Various morphological and physiological alterations in plant as result of soil compaction have also been discussed in this review.