Effect of reclamation treatments on microbial activity and phytotoxicity of soil degraded by the sulphur mining industry

Effects of Agricultural Management of Spent Mushroom Waste on Phytotoxicity and Microbiological Transformations of C, P, and S in Soil and Their Consequences for the Greenhouse Effect

The huge volumes of currently generated agricultural waste pose a challenge to the economy of the 21st century. One of the directions for their reuse may be as fertilizer. Spent mushroom substrate (SMS) could become an alternative to manure (M). A three-year field experiment was carried out, in which the purpose was to test and compare the effect of SMS alone, as well as in multiple variants with mineral fertilization, and in manure with a variety of soil quality indices-such as enzymatic activity, soil phytotoxicity, and greenhouse gas emissions, i.e., CO₂. The use of SMS resulted in significant stimulation of respiratory and dehydrogenase activity. Inhibition of acid phosphatase and arylsulfatase activity via SMS was recorded. SMS showed varying effects on soil phytotoxicity, dependent on time. A positive effect was noted for the growth index (GI), while inhibition of root growth was observed in the first two years of the experiment. The effect of M on soil respiratory and dehydrogenase activity was significantly weaker compared to SMS. Therefore, M is a safer fertilizer as it does not cause a significant persistent increase in CO₂ emissions. Changes in the phytotoxicity parameters of the soil fertilized with manure, however, showed a similar trend as in the soil fertilized with SMS.

A Circular Economy Approach to Restoring Soil Substrate Ameliorated by Sewage Sludge with Amendments

This study examined the use of an artificial soil substrate in a mine waste reclamation area and its effect on plant metabolic functions. Research was conducted by determining the relationship between the plants’ biochemical features and the properties of plant growth medium derived from post-flotation coal waste, sewage sludge, crushed stone and fly ash on the surface of the mine waste disposal area. Trees and shrubs were established on the material and allowed to grow for eight years. The study determined that the applied plants and the naturally occurring Taraxacum officinale were suitable for physio-biochemical assessment, identification of derelict areas and reclamation purposes. An evaluation of a soil substrate applied to post-mining areas indicated that it was beneficial for plant growth since it activated the metabolic functions of herbaceous plants, shrubs, and trees. The study showed that soil substrate can be targeted to improve plant stress tolerance to potentially toxic elements (PTEs). These data suggest the potential for growth and slower susceptible response to Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. It is possible that the constructed soil-substitute substrate (biosolid material) would be an effective reclamation treatment in areas where natural soil materials are polluted by PTEs. This observation may reflect a more efficient use of soil substrate released from the cycling of organic biogene pools, in accordance with the circular economy approach. In further studies related to land reclamation using sewage sludge amendments, it would be necessary to extend the research to other stress factors, such as salinity or water deficiency.

Influence of sulfur amendments on heavy metals phytoextraction from agricultural contaminated soils: A meta-analysis

Heavy metal pollution is becoming recurrent and threatens biota biosafety in many agricultural fields. Diverse solutions explore the application of amendments to enable remediation. Sulfur represents a nonmetallic chemical element that actively affects heavy metals phytoextraction, and promotes and alternatively mitigates soil functions. In this study, we conduct a meta-analysis to synthesize the current knowledge on the influence of sulfur amendments on plants heavy metals uptake from contaminated soil media. Random-effects model was used to summarize effect sizes from 524 data points extracted from 30 peer reviewed studies. The phytoextraction of cadmium, chromium and nickel were 1.6-, 3.3-, and 12.6-fold, respectively, higher when sulfur amendment was applied; while copper uptake was 0.3-fold lower. Irrespective of the sulfur type, heavy metal extraction increased with the raising sulfur stress. Individual organs showed significant differences of heavy metal uptake between sulfur applied and non-sulfur treatments, and combined organs did not. The heavy metals uptake in leaves and roots were higher in sulfur applied than non-sulfur applied treatments, while those in grain, husk, and stalks were lower. The heavy metals phytoextraction (response ratio) followed the order roots > leaves > stalk > grain > husk. Moreover, heavy metals uptake was 2-fold higher in the sulfur applied than the non-sulfur treatments under ideal (5.5-8) and alkaline conditions (8-14), and 0.2-fold lower under acidic pH (1-5.5). Cadmium, manganese and nickel, and chromium were the most extracted under sulfur application by Vicia sp., Sorghum sp. and Brassica sp., respectively; while chromium, manganese, and iron were the most uptake without sulfur amendments by Oryza sp., Zea sp. and Sorghum sp., respectively. Our study highlights that the influence of sulfur on heavy metal phytoextraction depends on the single or combined effects of sulfur stress intensity, sulfur compounds, plant organ, plant type, and soil pH condition.

Decay and erosion-related transport of sulfur compounds in soils of rubber based agroforestry

Elemental sulfur is intensively used to control weeds and rubber leaf diseases. However, the mechanisms contributing to elemental sulfur dissipation and decay (hereafter decay) in rubber agroforestry remains unclear. This study relates hydrological processes such as runoff and soil loss to the changes in soil total sulfur (S_tot) and sulfate (S-SO₄) in typical hillslope rubber agroforestry intercropped with cocoa in Xishuangbanna. The elemental sulfur decay kinetics were studied at two slopes (top and bottom) and three agrosystems (weed, no-weed and mixed). The results show that soil moisture and hydraulic conductivity was uniformly distributed in the experimental rubber agroforestry settings. Higher soil loss and runoff occurred in the bottom slope than the top slope, and in no-weed agrosystem than the herbaceous agrosystems (weed and mixed). The soil loss was mainly driven by runoff. Moreover, S_tot and S-SO₄ in runoff water were higher in weed agrosystem than no-weed agrosystems. Soil S_tot best fit a two-compartments kinetics model, with lower kinetic rates in elemental sulfur applied treatments than in the no-added elemental sulfur treatments, particularly for the weed agrosystem. The soil S_tot dissipation time 50% (DT₅₀) was 10-14 times higher in top slope than bottom slope; but 4 and 20 times higher in mixed and no-weed agrosystems, respectively, compared to the weed agrosystem. The soil S_tot and S-SO₄ contents negatively correlated with soil microbial respiration (CO₂ efflux), indicating an adverse influence of elemental sulfur on soil microbial activity. In short, elemental sulfur decay and its S-SO₄ transformation depended on soil moisture, runoff, soil erosion and soil CO₂, which are in turn affected by slope and agrosystem. This study not only clarifies the mechanisms of elemental sulfur dissipation and decay for its use as an environmental friendly agrochemical; but it also provides information to understand the contribution of runoff and soil loss on these mechanisms in rubber agroforestry.

Activity of selected enzymes and phosphorus content in soils of former sulphur mines

This paper presents phosphorus content, the activity of enzymes, and relationships between chemical properties in former sulphur mine soil ecosystems. Soil sampled 16 years after the completion of open-pit mining works at Machów, and 7 years after sulphur mining by the "melting" method was abandoned in the Jeziórko mine. In these soil samples were determined content of total (TP), mineral (MP), organic (OP), available (AP) phosphorus, the activity of catalase (CAT), dehydrogenases (DHA), alkaline (AlP) and acid (AcP) phosphatase, and metabolic metabolic quotient (qCO₂). Total phosphorus content in samples from the Machów mine ranged from 0.297 to 0.392 g kg^-1. In the soil from the vicinity Jeziórko, TP content was in the range 0.329-0.460 g kg^-1. The content of AP in soil from the vicinity of Machów range from 10.77 to 43.44 mg kg^-1, and near the Jeziórko mine from 5.73 to 18.03 mg kg^-1. Availability factor (AF) for phosphorus was calculated, which was higher in soil under the impact of the Machów mine compared to the soil near the of Jeziórko mine. The activity of AlP in soil around the Jeziórko mine was lower than in soils sampled near the Machów mine. Enzymatic activity and total carbon content were used to calculate the biochemical activity index (BA12), which was higher in soils under the impact of the Machów mine. The value of metabolic quotient (qCO₂) was low in the upper layers of the clarifier (Machów) and also 10 and 40 m from the borehole Jeziórko. The highest value of this parameter was observed in soil from the post-process waste dump at Machów (3.6 μgCO₂ [μgC mic]^-1 h^-1). A long-term human impact significantly affected the soil phosphorus under study and the physico-chemical properties, which led to a change in the enzymatic activity of soil.

Reclamation of Cultivated Land Reserves in Northeast China: Indigenous Ecological Insecurity Underlying National Food Security

The competition for land resources created by the need for food security and ecological security is intensifying globally. To resolve the issue of land scarcity in agriculture following rapid urbanization, China implemented its requisition–compensation balance policy of cultivated lands in 1997, the introduction of which consumed numerous areas of land, such as river shoal and bare land, through reclamation. Moreover, these reclaimed and newly cultivated lands were mainly distributed in the northern part of China. Most previous studies of this subject have only examined the overall balance of cultivated lands in well-developed regions, and there is a lack of knowledge about the indigenous gains and losses before and after reclamation in important areas such as northeast China. Therefore, this study selected two representative county-level units in northeast China as the study area to analyze the conversion of cultivated land reserves during 1996–2015, evaluate the performance of reclaimed cultivated lands in terms of quality and productivity and calculate reclamation-induced changes in ecosystem service value. The results indicated that by 2015 only 16.02% of the original cultivated land reserves remained unconverted; nearly 60% were reclaimed as cultivated lands and over 20% were converted to other land resources. River shoal and ruderal land were the primary resources for cultivated lands compensation, and marsh, bare land and saline-alkaline land were found to be converted the most thoroughly. The gain of 23018.55 ha reclaimed cultivated lands were of relatively inferior quality and lower productivity, contributing approximately 4.32% of total grain output. However, this modest gain was at the expense of a 768.03 million yuan ecosystem services loss, with regulating services and supporting services being undermined the most. We argue that even if northeast China continues to shoulder the responsibility of compensating for a majority of cultivated land losses, it still needs to carefully process reclamation and introduce practical measures to protect indigenous ecosystems, in order to better serve the local residents and ensure prolonged food security with sustainability.