Phosphorus deficiency is wide-spread due to the poor solubility of soil P and the rapid formation of poorly available P after P addition. Microbes play a key role in soil P dynamics by P uptake, ...solubilisation and mineralisation. Therefore a better understanding of the relationship between type of P amendment, microbial activity and changes in soil P pools is important for a better management of soil P. A P deficient soil was amended with two composts (low P or high P), two crop residues (low P or high P), and inorganic P (KH2PO4) at low and high P, and incubated for 56 days. Composts were added at 20gkg−1 resulting in a total P addition of 4.1mgkg−1 soil with the low P compost and 33.2mgkg−1 soil with the high P compost. The same amount of P was added with the other amendments (residues and inorganic P). All amendments increased cumulative respiration, but microbial biomass and the abundance of bacteria and fungi (assessed by phospholipid fatty acid analysis) increased significantly only in soils with organic amendments, with greater increases with residues. The concentration of the inorganic P pools NaHCO3-Pi, NaOH-Pi and HCl-P increased significantly within 5h after amendment, particularly with high P amendments. Over the following 56 days, labile inorganic P was converted mainly into non-labile inorganic P with inorganic P addition whereas labile and non-labile organic P was formed with organic amendments. It is concluded that organic P sources, particularly those with high P concentration can stimulate the formation of organic P forms in soils which may provide a long-term slow release P source for plants and soil organisms.
► Organic amendments (compost or residues) inorganic P were added at two P rates. ► Organic amendments induced strong increases in organic P pools. ► Inorganic P addition resulted in increases in inorganic P pools. ► Inorganic P was transformed to organic P pools particularly with organic amendments.
Present study reports the laboratory and field scale application of different organic and inorganic amendments to immobilize cadmium (Cd) and lead (Pb) in a co-contaminated alluvial paddy soil. For ...that purpose, lime, biochar, Fe-biochar and two composite amendments (CA) composed of biochar, lime, sepiolite and zeolite (CA1: composite amendment 1) and manure, lime and sepiolite (CA2: composite amendment 2) were firstly tested in an incubation experiment to ameliorate Cd and Pb co-contaminated alluvial soil. It was observed that liming and CA2 elevated the soil pH and reduced DTPA extractable Cd and Pb in the incubated soil leading to higher metal immobilization. Therefore, efficiency of lime and CA2 was further investigated in field conditions with mid rice as the test crop to evaluate field scale immobilization and precise application rate for the tested soil type. DTPA and CaCl2 extractable Cd (46 and 51%) and Pb (68 and 70%) in field soil were decreased with applied treatments. Speciation of Cd and Pb also promoted conversion of metal exchangeable contents to less-available forms. Activated functional groups on amendments’ surface (_OH bonding, C_O and CO, -O-H, Si–O–Si, carboxylic and ester groups) sequestered metals by precipitation, adsorption, ion exchange or electro static attributes. Application of lime at 2400 kg/acre (T4) and CA2 at 1200 kg/acre was more effective in reducing rice shoot and grains metal contents. Moreover, obtained results in terms of pH, extractable content, speciation and yield, and microanalysis of amendments highlights the remarkable efficiency of lime and composite amendment to sorb Cd and Pb providing the key evidence of these amendments for metals immobilization and environmental remediation. Considering these results, lime and CA2 are potential amendments for co-contaminated rice field especially in context of alluvial soil.
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•Inorganic, organic and composite amendments decreased the DTPA extractable metals.•Lime addition elevates incubated and field soil pH.•Cd and Pb speciation reduced exchangeable form of metals.•Lime and CA2 were effective in reducing metal availability in alluvial soil.
Inorganic and organic additives have potential to remediate metal polluted sites but their composite application was more helpful in reducing Cd and Pb availability in co-contaminated alluvial soil.
In this field experiment, sewage sludge was applied at 0, 5, 10, and 50
t
ha
−1, and the availability of Cd, Ni, Pb, and Zn was assessed both by ryegrass uptake and by DTPA extractions. The aim was ...to investigate the role of important soil parameters, particularly pH, on heavy metal availability. It was found that metal uptake and extractability increased significantly in the 50
t
ha
−1 treatment. In the 16th week of the experiment there was a significant, although temporary, increase in DTPA-extractable Cd, Ni, and Zn concentrations. Metal concentrations in ryegrass were also significantly elevated in week 20 compared to the subsequent cuttings. These fluctuations in both DTPA and ryegrass uptake occurred only at 50
t
ha
−1 and were probably induced by a sudden pH decrease measured in the same treatment in week 16. This suggests that soils which have received high applications of sewage sludge may be prone to fluctuations in metal availability.
Accurately measuring the concentration of methylmercury (MeHg) is a critical part of Hg research. While analytical methods of MeHg have not been validated for paddy soils, which are one of the most ...important and active sites of MeHg production. Here we compared two methods most widely used to extract MeHg from paddy soils, i.e., CuSO4/KBr/H2SO4-CH2Cl2 (referred to as acid extraction) and KOH-CH3OH (referred to as alkaline extraction). By evaluating the formation of MeHg artifact using Hg isotope amendments and quantifying the extraction efficiency using the standard spike in 14 paddy soils, we propose that alkaline extraction is an optimal choice for paddy soils, with negligible MeHg artifact (accounting for 0.62–8.11 % of the background MeHg) and consistently high extraction efficiency (81.4–114.6 % for alkaline extraction compared with 21.3–70.8 % for acid extraction). Our finding highlights the importance of suitable pretreatment and appropriate quality controls during the measurement of MeHg concentrations.
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•Alkaline extraction is an optimal method for paddy soils with high extraction efficiency while negligible artifact production.•Acid extraction may lead to underestimations in soil MeHg due to the low extraction efficiency.•Appropriate quality control is essential to ensure low artifact formation and high extraction efficiency.
•Effects of rhamnolipid (RL) and particle size (IPS) on composting were studied.•RL at 0.15% and IPS of 15mm reduced the two-stage composting time to 24days.•Physico-chemical and biological ...characteristics explain the rapid decomposition.•Microbial communities, nutrient contents, and cellulose degradation are optimized.
Composting is a potential alternative to green waste incineration or deposition in landfills. The effects of the biosurfactant rhamnolipid (RL) (at 0.0%, 0.15%, and 0.30%) and initial compost particle size (IPS) (10, 15, and 25mm) on a new, two-stage method for composting green waste was investigated. A combination of RL addition and IPS adjustment improved the quality of the finished compost in terms of its physical characteristics, pH, C/N ratio, nutrient content, cellulose and hemicellulose contents, water-soluble carbon (WSC) content, xylanase and CMCase activities, numbers of culturable microorganisms (bacteria, actinomycetes, and fungi), and toxicity to germinating seeds. The production of a stable and mature compost required only 24days with the optimized two-stage composting method described here rather than the 90–270days required with traditional composting. The best quality compost was obtained with 0.15% RL and an IPS of 15mm.
