Cadmium mobility, uptake and anti-oxidative response of water spinach (Ipomoea aquatic) under rice straw biochar, zeolite and rock phosphate as amendments

Soil contamination with heavy metals, such as Cd and Pb, has caused severe health and environmental risks all over the world. Possible eco-friendly solutions for Cd and Pb immobilization were required to reduce its mobility through various cost-effective amendments. A laboratory incubation study was conducted to assess the efficiency of biochar (BC), zeolite (ZE), and rock phosphate (RP) as passivators for the stabilization of Cd and Pb in paddy soil as well as soil microbial biomass. Various extraction techniques were carried out: a sequential extraction procedure, the European Community Bureau of Reference (BCR), toxicity characteristic leaching procedure (TCLP) test, and single extraction with CaCl2. The impact of passivators on soil pH, dissolved organic carbon (DOC), and microbial biomass (carbon, nitrogen, and phosphorus) was examined in the metal contaminated soil. The results showed that the exchangeable portion of Cd in soil was significantly reduced by 34.8, 21.6, and 18.8% with ZE, RP, and BC at a 3% application rate, respectively. A similar tendency of reduction in Pb soluble portion was observed by ZE (9.6%), RP (20%), and BC (21.4%) at a 3% application rate. Moreover, the TCLP leachate of Cd and Pb was apparently reduced by 17 and 30.3% with BC at a 3% application dose, respectively, when compared to the control. Soil pH, nutrients, and microbial biomass C, N, and P were significantly increased with the addition of BC, RP, and ZE passivators. The results showed that the incorporation of BC, ZE, and RP significantly reduced the Cd and Pb mobility in paddy soil as well as enhanced soil nutrients and microbial biomass. Overall, among all the amendments, rice straw derived-BC performed better for Cd and Pb immobilization in paddy soil.

Rice straw biochar mitigates N2O emissions under alternate wetting and drying conditions in paddy soil

A screenhouse experiment was conducted to study the effect of four rates of rice straw biochar (0, 1, 2 and 4%) on the bioavailability and accumulation of cadmium (Cd) by Indian mustard (Brassica juncea) in sewage water irrigated soil artificially spiked with Cd. Immobilization of Cd by rice straw biochar was assessed on the basis of DTPA-extractable Cd in soil and its content in shoots of Indian mustard. The results revealed a linear decrease in DTPA-Cd with the addition of rice straw biochar. Addition of biochar at the highest level (4%) decreased the mean Cd content in soil and in plant by 38.1 and 60.1%, respectively. Biochar addition increased dry matter yield (DMY) of Indian mustard and maximum yield increase of 19.3% was observed at 2% addition. The increase in DMY was decreased to 2.6% at 4% addition of biochar. The study indicated that rice straw biochar can be used as a remediation measure for contaminated sites and may prove to be a viable option for managing agricultural residues.

In the present study, efficiency of different biochars (BCs) on cadmium (Cd) immobilization and its bioavailability to spinach were investigated. In the first experiment, Cd-spiked soil was amended with treatments (T1 = control, T2 and T3 = cotton stalk biochar (CBC) 2% and 5%, T4 and T5 = rice straw biochar 2% and 5%) and incubated for 120 days. In the second experiment, spinach was grown in pots using three soils (a normal soil, a Cd-spiked soil, and a sewage-irrigated soil) after application of CBC and rice straw biochar (RBC) (2% w/w each) in each soil. In the field experiments, spinach was grown at two sites with six treatments including T0 = control, T1 and T2 (RBC 5 and 10 ton ha−1), T3 and T4 (CBC 5 and 10 ton ha−1). The results of our experiments showed a significant impact of BCs on soil pH, EC, soil organic matter, and Cd bioavailability. The plant growth parameters were also influenced positively by application of BC in both pot and field experiments. In field experiments, plant population and fresh biomass at different sites varied significantly. The Cd concentration in plants was lower when grown in treated soils. Moreover, there was a significant increase in soluble Si and phosphorus concentrations in plants and this had significant correlation with Cd concentration in plants.

Biochar has been widely used for immobilizing heavy metals in soils due to its favorable sorption capacity. Previous investigations on heavy metal immobilization in waters by biochar are conducted in laboratory. Knowledge about the long-term effects of in situ biochar application on water bodies contaminated by heavy metals remains scarce. In this research, biochar was derived from cadmium (Cd)-accumulated rice straw. A 35-d laboratory simulation and a three-year field enclosure experiment were carried out to assess the impacts of biochar application on Cd behavior in a water–sediment system of a historically Cd-contaminated irrigation pond. Results indicated that the pH of sediment and overlying water increased with biochar addition in both the lab and field experiments. The rice-straw biochar transformed the Cd in sediments from the exchangeable to residual fraction, because biochar addition increased the pH values and organic matter contents in sediment, leading to the sorption, sequestration, and passivation of Cd by sediment. The Cd concentration in overlying water decreased with the increase in biochar addition, and it continuously decreased with repeated annual application. Overall, for long-term effects of biochar addition on soluble Cd concentrations, the repeated annual addition of 2% biochar exhibited better performance than the repeated annual addition of 1% biochar and one-time addition of 6% biochar. This study provided a proper mode of utilizing rice-straw biochar to treat Cd-contaminated irrigation water in mining regions.

This research aims to compare fresh biochar and NPK-enriched biochar and their decomposition levels and nutrient absorption efficiency in acid soil with soybean. Factorial randomized block design was used in this experiment and consisted of two factors. The first factor, biochar source, comprised four levels: B0: biochar without NPK, B1: rice straw biochar + NPK, B2: soybean straw biochar + NPK, and B3: wood biochar + NPK. The second factor, biochar enrichment, comprised four levels: D1: 0.5 tons ha<sup>-1</sup>, D2: 2.5 tons ha<sup>-1</sup>, D3: 5.0 tons ha<sup>-1</sup>, and D4: 10 tons ha<sup>-1</sup>. Each treatment was replicated three times, yielding 48 experiment units. The results showed that biochar enrichment with NPK affected the decomposition level. The percentage of increasing decomposition in enriched wood biochar (0.09%) was lower than rice (0.28%) and soybean (0.53%) straw biochar. An increase in NPK absorbance efficiency and soybean dry weight was evident in NPK-enriched biochar. The highest N absorbance efficiency occurred in wood biochar (21%), followed by soybean and rice straw biochar, respectively, while the highest P and K absorbances were found in rice straw biochar (35% and 26%, respectively), followed by wood and then soybean biochar.

Methane emissions and associated microbial activities from paddy salt-affected soil as influenced by biochar and cow manure addition

Pyrolysis temperature affects pore characteristics of rice straw and canola stalk biochars and biochar-amended soils

Biochar applied to soil can reduce nitrous oxide (N2O) emissions produced by freeze–thaw processes. Nonetheless, how biochar modification affects N2O emissions during freeze–thaw cycles is not completely clear. In our research, during freeze–thaw cycles, microcosm experiments were conducted to investigate the effects of maize straw biochar (MB) or rice straw biochar (RB) addition on soil N2O emissions under different water conditions. The N2O emissions peaked at the initial stage of thawing in all the soils, and the total N2O emissions were considerably greater in the flooded soils than in the nonflooded soils. Compared with the soils without biochar addition, RB and MB amendments inhibited N2O emissions by 69 and 67%, respectively. Moreover, after biochar addition, the abundance of AOB amoA genes decreased by 9–13%. Biochar addition significantly decreased the content of microbial biomass nitrogen (MBN) in flooded soil during thawing, which was significantly correlated with N2O emissions and nitrification and denitrification communities. The PLS-PM further revealed that biochar can inhibit the production and emission of soil N2O by reducing soil MBN during soil thawing. In addition, soil moisture directly significantly affects N2O emissions and indirectly affects N2O emissions through its influence on soil physicochemical properties. Our results revealed the important function of biochar in decreasing the emission of N2O in flooded soil during freeze–thaw cycles.

Combined use of biochar and phosphate rocks on phosphorus and heavy metal availability: A meta-analysis

Growth and elemental uptake of Trifolium repens in response to biochar addition, arbuscular mycorrhizal fungi and phosphorus fertilizer applications in low-Cd-polluted soils

Effect of bamboo and rice straw biochars on the mobility and redistribution of heavy metals (Cd, Cu, Pb and Zn) in contaminated soil

PurposeThe study aimed to determine the effect of the addition of innovative combinations of organic-mineral mixtures obtained from biochar (BC), zeolite (Z), soil (S), poultry litter (PL), and slurry (SL) to post-flotation sediment (PFS) on (i) heavy metal mobility, (ii) heavy metal accumulation in willow, and (iii) PFS respiratory activity.Materials and methodsThe tests were carried out under laboratory conditions in containers with 500 g of PFS, to which 1% (w/w) of organic-mineral mixtures were added. Willow was grown for 90 days on substrates with the addition of organic and mineral mixtures.Results and discussionThe addition of mixtures BC + Z + S + PL and BC + Z + S + SL to PFS significantly reduced the pH to, respectively, 7.12 and 7.02. This can be attributed to the release of the hydrogen load combined with organic anions deriving from the mineralisation of organic materials and the nitrification process. The addition of BC + Z and BC + Z + S mixtures to PFS reduced the content of Zn-H2O by 65%, Cd-H2O by 48%, and Ni-H2O by 30%. The addition of BC + Z + S + PL and BC + Z + S + PL mixtures to PFS increased the content of water-extracted Pb, respectively, 40 and over 60 times. The content of bioavailable heavy metals (extraction with 1 M NH4NO3) in PFS was comparable in all treatments to which mixtures were added. Altered mobility of heavy metal ions may be associated with a change of substrate properties, including redox potential, pH value, as well as the introduction into the soil of materials with significantly developed sorption surfaces. In the first 2 weeks of incubation of mixtures with PFS, respiratory activity was very low, except for that in BC + Z + S + PL and BC + Z + S + SL treatments. In these treatments, oxygen consumption was more than 50 times higher compared to the control treatment and more than 10 times higher in relation to BC + Z and BC + Z + S treatments.ConclusionsThe mixtures of BC + Z and BC + Z + S effectively reduced the content of water-extracted heavy metals in PFS. BC + Z + S + PL and BC + Z + S + PL mixtures were not effective in reducing water-extracted mobile heavy metals in PFS. The introduction into PFS of mixtures partially composed of biologically unstable materials (PL, SL) increased the biochemical activity measured by respiratory activity and reduced biomass increment of willow aerial parts. The adverse response of willow to the introduction of mixtures with poultry litter or slurry into PFS indicates the need to verify the amount of these materials in the mixtures or to stabilise them by biological or thermal processes.Graphical abstract

Horizontal gene transfer is a key determinant of antibiotic resistance genes profiles during chicken manure composting with the addition of biochar and zeolite

Inhibition of polycyclic aromatic hydrocarbon (PAHs) release from sediments in an integrated rice and crab coculture system by rice straw biochar