Remediation approaches for polycyclic aromatic hydrocarbons (PAHs) contaminated soils: Technological constraints, emerging trends and future directions.

Vermicomposting is a process in which earthworms are used to convert organic materials into humus-like material known as vermicompost. A number of researchers throughout the world have found that the nutrient profile in vermicompost is generally higher than traditional compost. In fact, vermicompost can enhance soil fertility physically, chemically and biologically. Physically, vermicompost-treated soil has better aeration, porosity, bulk density and water retention. Chemical properties such as pH, electrical conductivity and organic matter content are also improved for better crop yield. Nevertheless, enhanced plant growth could not be satisfactorily explained by improvements in the nutrient content of the soil, which means that other plant growth-influencing materials are available in vermicomposts. Although vermicomposts have been shown to improve plant growth significantly, the application of vermicomposts at high concentrations could impede growth due to the high concentrations of soluble salts available in vermicomposts. Therefore, vermicomposts should be applied at moderate concentrations in order to obtain maximum plant yield. This review paper discusses in detail the effects of vermicompost on soil fertility physically, chemically and biologically. Future prospects and economy on the use of organic fertilizers in the agricultural sector are also examined.

The use of vermicompost in organic farming: overview, effects on soil and economics

Comparing straw, compost, and biochar regarding their suitability as agricultural soil amendments to affect soil structure, nutrient leaching, microbial communities, and the fate of pesticides

Management of municipal solid waste is a global problem and is faced by all developing countries. The rapid pace of increase in population, economic growth, urbanization and industrialization is coupled with accelerated solid waste generation. In most of the developing countries wastes are either scattered in urban centers or disposed off unplanned in low lying areas or open dumps. The lack of infrastructure for collection, transportation, treatment and disposal of solid waste, proper solid waste management planning, insufficient financial resources, technical expertise and public attitude have made the situation exasperating due to which several environmental and health related problems are increasing. Though, there are many negative issues related to solid waste, it also provides many opportunities that not only mitigates its negative impact but also helps in meeting the demand for energy and employment generation as well as in soil health improvement. Keeping in mind the present situation the current review was planned with the objective to overlook the challenges and opportunities faced during urban solid waste management in developing countries like India.

Urban solid waste management in the developing world with emphasis on India: challenges and opportunities

The aim of this study was to investigate the effectiveness of compost and vermicompost as soil conditioners in alleviating salt-affected soils and increasing maize productivity. A greenhouse trial, consisting of seven soil amendment treatments in a completely randomized design with three replications, was carried out at Khon Kaen University, Thailand, during the rainy season of 2011. Plant height and total dry matter of maize increased in treatments with compost and vermicompost application when compared with the control (no fertilizer) in two types of soils (saline and nonsaline) during the growing season. Soil pH and electrical conductivity in saturation paste extracts were decreased by compost and vermicompost amendments with or without earthworms when compared with unamended treatments in the saline soil. Compost and vermicompost amendments improved cation exchange capacity, soil organic carbon, total nitrogen and extractable phosphorus in both soils. These amendments also increased exchangeable K+, Ca2+ and Mg2+ while decreasing exchangeable Na+ in the saline soil, which suggested that Ca2+ was exchanged for Na+, exchangeable Na+, then leached out, and soil salinity reduced as a result. Soil microbial activities including microbial C and N and basal soil respiration were improved by the application of compost and vermicompost amendments with or without earthworms when compared with the control in both soils. This experiment showed that the compost and vermicompost were effective in alleviating salinity and improving crop growth. Copyright © 2013 John Wiley & Sons, Ltd.

Soil Properties and Maize Growth in Saline and Nonsaline Soils using Cassava‐Industrial Waste Compost and Vermicompost with or Without Earthworms

Vermicomposting differs from conventional composting because the organic material is processed by the digestive systems of worms. The egested casts can be used to improve the fertility and physical characteristics of soil and potting media. In this study, the effects of earthworm casts (EW), conventional compost (CP) and NPK inorganic fertilizer (FT) amendments on N mineralization rates, microbial respiration, and microbial biomass were investigated in a laboratory incubation study. A bioassay with wheat ( Triticum aestivium L.) was also conducted to assess the amendment effects on plant growth and nutrient uptake and to validate the nutrient release results from the incubation study. Both microbial respiration and biomass were significantly greater in the CP treatment compared to EW treatment for the initial 35 days of incubation followed by similar respiration rates and biomass to the end of the study at 70 days of incubation. Soil NO 3 − increased rapidly in the EW and CP treatments in the initial 30 days of incubation, attaining 290 and 400 mg N kg −1 soil, respectively. Nitrate in the EW treatment then declined to 120 mg N kg −1 soil by day 70, while nitrate in the CP treatment remained high. While ammonium levels decreased in the CP treatment as nitrate level increased with increasing incubation time, a low level of ammonium was maintained in the EW treatment throughout the incubation. The wheat bioassay study included two additional cast treatments (EW-N and EW2) to have treatments with higher levels of N input. Plants grown with CP or FT treatment had a lower shoot biomass and higher shoot N content than in EW-N and EW-2 treatments, and also showed symptoms of salinity stress. Ionic strength and other salinity indicators in the earthworm cast treatments were much lower than in the CP treatment, indicating a lower risk of salinity stress in casts than in compost. All cast and compost amendments significantly increased wheat P and K uptake compared to either the non-amended control or the mineral fertilizer treatment. The results show that casts are an efficient source of plant nutrients and that they are less likely to produce salinity stress in container as compared to compost and synthetic fertilizers.

Effects of earthworm casts and compost on soil microbial activity and plant nutrient availability

Separating earthworms from organic media using an electric field

Adding earthworms to an organic soil amendment increases nutrient mineralization and therefore the efficiency of organic fertilizers. A device controlling the earthworms feeding rate would allow a nutrient release in sync with plant uptake. A preliminary experiment shows the need for containment to maintain an optimal feed to earthworm ratio. A lab experiment also demonstrated the repelling effect of light on earthworms. Since earthworms crawl across physical obstacles, containment was attempted using a 5 mA underground electric field created across 40 cm deep soil electrodes. In a second treatment a surface light source was used. The earthworm count migrating across a nutrient gradient into nutrient-rich traps, relative to a control, was evaluated for each treatment. The electric field combined with the surface light source was 90% efficient at containing earthworms. In another experiment, a preliminary model was derived by varying electric current levels and spacing between electrodes. Next, aeration was tested as a means to control the feeding rate of earthworms. An aeration manifold delivering 3 or 6 c.c. of air per min per pot was used. The rate at which earthworms ingested 3 ml of blue cornflower paste placed at the surface of the pot, relative to a control, was evaluated. Results showed that delivering 6 c.c. of air per min at a depth of 1.5 cm increases the feeding rate. More experiments are needed both to accurately model the efficiency of the electric field at containing earthworms and the effect of forced soil aeration on the feeding rate of earthworms.

Developing Field Containment Techniques of Earthworms to Increase Organic Fertilizer Efficiency

Earthworms have been shown to effectively process biodegradable organic waste and increase the
availability of nutrients to plants in the final product, vermi-compost, compared to the raw material. After
processing earthworms are mechanically separated from the vermi-compost and used for processing more
waste or sold. This study investigated whether an electric field could be used to separate earthworms from
vermi-compost, since it is known earthworms are repelled by an electric field. The effectiveness with which an
earthworm is repelled depends on the voltage created across the earthworm. Select variables affecting this
voltage were varied in a set of experiments using earthworms placed in a 2.8 x 2.8 x 7.5 cm soil slab at a
density corresponding to 150 earthworms per liter. The variables were the level of electric current at the
threshold of the soil slab (the point beyond which earthworms were to be repelled), earthworm diameter and
resistance (species-dependent), soil electrode depth and spacing. Effectiveness of the electric field was
calculated as a function of the number of earthworms that exited the soil slab. Spatial voltage values were
evaluated in each replicate in order to identify the voltage drops in the soil slab and derive the corresponding
threshold electric current. Results showed that the effectiveness of the electric field was logarithmically
proportional to the voltage generated across earthworms, at a given electrodes spacing, up to the point where
earthworm mortality started to occur. At higher voltages the electric field effectiveness decreased exponentially
due to mortality. The time where all potential earthworms exited a soil slab increased exponentially up to peak
effectiveness, and decreased exponentially after that. The resulting mathematical models can be used to aid in
the design of an array of soil rods connected to a power source to repel earthworms from the compost medium.

Hala Chaoui

Papers

Effects of earthworm casts and compost on soil microbial activity and plant nutrient availability

Separating earthworms from organic media using an electric field

Developing Field Containment Techniques of Earthworms to Increase Organic Fertilizer Efficiency

Modeling the Effectiveness of an Electric Field at Repelling Earthworms