Soil health improvement by inoculation of indigenous microalgae in saline soil

Using biological methods to improve saline soils is recognized as an eco-friendly and sustainable way. In this study, two indigenous algae YJ-1 and YJ-2 screened from salinized farmland were inoculated into saline soils with different salinization levels to investigate their potential in enhancing soil health by laboratory microcosm experiment. The results showed that individual inoculation of the two algae quickly resulted in the formation of algal crusts, and the chlorophyll content in the saline soils gradually increased with the incubation time. The soil pH decreased significantly from the initial 8.15-9.45 to 6.97-7.56 after 60-day incubation. The exopolysaccharides secretion and the activities of catalase, sucrase, and urease in saline soils also increased. Microalgal inoculation increased soil organic matter storage, while decreasing the available nutrient contents possibly due to the depletion of microalgal growth. PCA and PCC results identified that microalgal biomass as the predominant variable affecting soil quality. Overall, these data revealed the great potential of microalgae in the amelioration of saline soils, especially in pH reduction and enzyme activity enhancement. This study will provide the theoretical foundation for improving saline soils via algalization.

Microbial Catabolic Activity: Methods, Pertinence, and Potential Interest for Improving Microbial Inoculant Efficiency

Microbial catabolic activity (MCA) defined as the degrading activity of microorganisms toward various organic compounds for their growth and energy is commonly used to assess soil microbial function potential. For its measure, several methods are available including multi-substrate-induced respiration (MSIR) measurement which allow to estimate functional diversity using selected carbon substrates targeting specific biochemical pathways. In this review, the techniques used to measure soil MCA are described and compared with respect to their accuracy and practical use. Particularly the efficiency of MSIR-based approaches as soil microbial function indicators was discussed by (i) showing their sensitivity to different agricultural practices including tillage, amendments, and cropping systems and (ii) by investigating their relationship with soil enzyme activities and some soil chemical properties (pH, soil organic carbon, cation exchange capacity). We highlighted the potential of these MSIR-based MCA measurements to improve microbial inoculant composition and to determine their potential effects on soil microbial functions. Finally, we have proposed ideas for improving MCA measurement notably through the use of molecular tools and stable isotope probing which can be combined with classic MSIR methods. Graphical abstract describing the interrelation between the different parts and the concepts developed in the review.

Seasonal Variation of Soil Quality in a Semi-deciduous Northern Tropical Forest of Nagaland, India

To assess the seasonal changes in soil parameters and the soil quality of a semi-deciduous forest in Nagaland, tropical forest soil samples were tested for 10 physical and chemical variables. Apart from clay content, EC, and CEC, the rest of the parameters showed a seasonal mean significant difference at p < .05 level. Based on the principal component analysis, available nitrogen (N_av) and electrical conductivity (EC) were included in a minimum data set and are regarded to best represent the system attributes. In both additive and weighted soil quality method, maximum SQI was recorded in autumn season. The research summarized that seasonal variations can influence soil characteristics and soil quality through its aggregate effects. Considering the result obtained from the present study, the approach we have used in soil quality assessment would be suitable for primarily screening the tropical forest soil status. This would ultimately pave ways for future management and mitigation plans to facilitate the improvement of forest health and aid to biodiversity conservation.

Green infrastructure influences soil health: Biological divergence one year after installation

Global threats to soils remain one of the greatest concerns and challenges of the 21st century. Built landscapes have profound local and global effects because they create urban heat islands, increase habitat fragmentation, and reduce biological diversity. Additionally, impervious surfaces alter natural watersheds and reduce infiltration increasing runoff that leads to erosion and soil degradation. To combat these effects, green infrastructure (GI) practices, like water harvesting rain gardens, are implemented in the Southwest United States to restore natural ecological function, yet little is known about how GI impacts soil health. Soil health can be measured using indicators that include physical, chemical, and biological characteristics that support ecosystem processes. This study aimed to evaluate changes in water holding capacity, bulk density, pH, electrical conductivity, Gibbs free energy, species richness and Shannon diversity in response to rain gardens that received different inputs (frequency and amount) and sources of harvested water (rain, municipal, greywater) one year after installation. We hypothesized that soil health indicators in GI diverge from the unaltered control treatment one year following installation. Although physical and chemical indicators were comparatively less sensitive to GI treatments than biological indicators, they varied within treatments after one year of GI management (pH increased: H = 36.37; p-value = 0.00; electrical conductivity decreased: H = 33.94; p-value = 0.00). Overall, we observed significantly higher soil microbial diversity (F = 4.29; p-value = 0.015) and richness (F = 4.02; p-value = 0.019) in surface soils in GI treatments after one year of management. Our findings suggest GI practices enhanced soil biological health which may lead to positive feedbacks that assist gradual changes in the abiotic environment thus enhancing soil health over time. These findings have broad implications for effectively assessing the success of GI management practices over short time periods using soil biological health indicators.

Temporal characterisation of soil-plant natural recovery related to fire severity in burned Pinus halepensis Mill. forests

Despite Mediterranean ecosystems' high resilience to fire, both climate and land use change, and alterations in fire regimes increase their vulnerability to fire by affecting the long-term natural recovery of ecosystem services. The objective of this work is to study the effects of fire severity on biochemical soil indicators, such as chemical composition or enzymatic activity, related to time after fire and natural vegetation recovery (soil-plant interphase). Soil samples from three wildfires occurring 3, 15 and 21 years ago were taken in the south-eastern Iberian Peninsula (semiarid climate). Sampling included three fire severity levels in naturally regenerated (and changing to shrublands) Pinus halepensis Mill. forests. In the short-term post-fire period, phosphorus concentration, electrical conductivity and urease activity were positively linked to fire severity, and also influenced β-glucosidade activity in a negative relationship. During the 15-21-year post-fire period, the effects related to medium-high fire severity were negligible and soil quality indicators were linked to natural regeneration success. The results showed that most soil properties recovered in the long term after fire (21 years). These outcomes will help managers and stakeholders to implement management tools to stabilise soils and to restore burned ecosystems affected by medium-high fire severity. Such knowledge can be considered in adaptive forest management to reduce the negative effects of wildfires and desertification, and to improve the resilience of vulnerable ecosystems in a global change scenario.

Impact of potato cultivation and cattle farming on physicochemical parameters and enzymatic activities of Neotropical high Andean Páramo ecosystem soils

The Andean Páramos are high mountain ecosystems whose soils are essential for the management of South American water resources, but research on anthropic impacts to these soils is currently minimal and insufficient. The objective of this study was to evaluate the impacts of potato (Solanum tuberosum) cultivation and livestock on the physicochemical parameters and enzymatic activities that determine the soil quality of the Neotropical high Andean Páramo ecosystem in the Nevados National Natural Park (Nevados NNP) in Colombia. It was hypothesised that sites with potato crops and livestock farming would exhibit significant changes in soil physicochemical parameters and enzymatic activities compared with Páramo sites that have been conserved without agriculture. Samples were collected from soils under potato cultivation, livestock and Páramo (subject to the lowest degree of human intervention possible), on three farms in the El Bosque District at three different altitudes (Buenos Aires, El Edén and La Secreta) during two seasons (dry and rainy). The results showed that none of the physical parameters under study presented statistically significant differences due to the type of use (livestock, potato crop or Páramo), season of sampling (dry or rainy season) or altitude (different farms). The chemical parameters that statistically significantly differed due to land use were organic carbon, cation exchange capacity, calcium, potassium, and ammonium and those that showed statistically significant differences associated with the sampling timing were organic carbon, nitrogen, cation exchange capacity, total carbon, C/N and nitrate. Additionally, there were differences in organic carbon due to the altitude of the farms. With respect to enzymatic activities, those of β-glucosidase, phosphodiesterase and urease significantly decreased in soils under potato cultivation and livestock relative to those of Páramo, but those of acid phosphatase and protease increased significantly under potato cropping and livestock. The activities of β-glucosidase, acid phosphatase, alkaline phosphatase, phosphodiesterase and protease were higher during the dry season than the rainy season, and the activities of β-glucosidase, acid phosphatase and urease decreased statistically in the lower-altitude farm (La Secreta). These decreases in enzymatic activities are attributable to changes in the organic carbon of the soil. This study provides a novel insight on the relationships between land use and the physicochemical parameters and enzymatic activities of Páramo soils (which have been minimally studied to date) at different altitudes and during different seasons. The results suggest that changes in agricultural practices should be implemented to maintain the organic carbon of soil and, therefore, its enzymatic activities.

Effects of land use and land cover on selected soil quality indicators in the headwater area of the Blue Nile basin of Ethiopia

Understanding changes in soil quality resulting from land use and land management changes is important to design sustainable land management plans or interventions. This study evaluated the influence of land use and land cover (LULC) on key soil quality indicators (SQIs) within a small watershed (Jedeb) in the Blue Nile Basin of Ethiopia. Factor analysis based on principal component analysis (PCA) was used to determine different SQIs. Surface (0-15 cm) soil samples with four replications were collected from five main LULC types in the watershed (i.e., natural woody vegetation, plantation forest, grassland, cultivated land, and barren land) and at two elevation classes (upland and midland), and 13 soil properties were measured for each replicate. A factorial (2 × 5) multivariate analysis of variance (MANOVA) showed that LULC and altitude together significantly affected organic matter (OM) levels. However, LULC alone significantly affected bulk density and altitude alone significantly affected bulk density, soil acidity, and silt content. Afforestation of barren land with eucalypt trees can significantly increase the soil OM in the midland part but not in the upland part. Soils under grassland had a significantly higher bulk density than did soils under natural woody vegetation indicating that de-vegetation and conversion to grassland could lead to soil compaction. Thus, the historical LULC change in the Jedeb watershed has resulted in the loss of soil OM and increased soil compaction. The study shows that a land use and management system can be monitored if it degrades or maintains or improves the soil using key soil quality indicators.

SF Box--a tool for evaluating the effects on soil functions in remediation projects

Although remediation is usually aimed at reducing the risks posed by contaminants to human health and the environment, it is also desirable that the remediated soil within future green spaces is capable of providing relevant ecological functions, e.g., basis for primary production. Yet while addressing a contamination problem by reducing contaminant concentration and/or amounts in the soil, the remedial action itself can lead to soil structure disturbances, decline in organic matter and nutrient deficiencies, and in turn affect a soil's capacity to carry out its ecological soil functions. This article presents the Soil Function Box (SF Box) tool that is aimed to facilitate integration of information from suggested soil quality indicators (SQIs) into a management process in remediation using a scoring method. The scored SQIs are integrated into a soil quality index corresponding to 1 of 5 classes. SF Box is applied to 2 cases from Sweden (Kvillebäcken and Hexion), explicitly taking into consideration uncertainties in the results by means of Monte Carlo simulations. At both sites the generated soil quality indices corresponded to a medium soil performance (soil class 3) with a high certainty. The main soil constraints at both Kvillebäcken and Hexion were associated with biological activity in the soil, as soil organisms were unable to supply plant-available N. At the Kvillebäcken site the top layer had a content of coarse fragment (ø > 2 mm) higher than 35%, indicating plant rooting limitations. At the Hexion site, the soil had limited amount of organic matter, thus poor aggregate stability and nutrient cycling potential. In contrast, the soil at Kvillebäcken was rich in organic matter. The soils at both sites were capable of storing a sufficient amount of water for soil organisms between precipitation events.