Effects of Biochar on the Net Greenhouse Gas Emissions under Continuous Flooding and Water-Saving Irrigation Conditions in Paddy Soils

Critical evaluation of biochar utilization effect on mitigating global warming in whole rice cropping boundary

Biochar and compost were accepted as a stable organic amendment to increase soil C stock as well as to decrease greenhouse gas (GHG) emissions in rice paddy soils. However, in most studies, their effect on GHG flux was evaluated only within the cropping boundary without considering industrial processes. To compare the net effect of these organic amendment utilizations on global warming within the whole rice cropping system boundary from industrial process to cropping, fresh, compost, and biochar manures were applied at a rate of 12 Mg ha^-1 (dry weight) in a rice paddy, and total GHG fluxes were evaluated. Compared with fresh manure, compost utilization decreased net global warming potential (GWP) which summated GHG fluxes and soil C stock change with CO₂ equivalent by 43% within rice cropping boundary, via a 25% decrease of CH₄ flux and 39% increase of soil C stock. However, 34 Mg CO₂-eq. of GHGs were additionally emitted during composting to make 12 Mg of compost and then increased the net GWP by 34% within the whole system boundary. In comparison, biochar changed paddy soil into a GHG sink, via 56% decrease of CH₄ flux and 13% increase of soil C stock. However, pyrolysis emitted a total of 0.08 and 19 Mg CO₂-eq. of GHGs under with and without syngas recycling system, respectively, to make 12 Mg of biochar. As a result, biochar utilization decreased net GWP by approximately 28-70% over fresh manure within the whole system boundary. Rice grain productivity was not discriminated between biochar and compost manures, but compost considerably increased grain yield over fresh manure. Consequently, biochar utilization significantly decreased GHG intensity which indicates net GWP per grain by 33-72% over fresh manure, but compost increased by 22%. In conclusion, biochar could be a sustainable organic amendment to mitigate GHG emission impact in the rice paddy, but compost should be carefully selected.

The impact of pristine and modified rice straw biochar on the emission of greenhouse gases from a red acidic soil

With the growing awareness of environmental impacts of land degradation, pressure is mounting to improve the health and productivity of degrading soils, which could be achieved through the use of raw and modified biochar materials. The primary objective of the current study was to investigate the efficiency of pristine and Mg-modified rice-straw biochar (RBC and MRBC) for the reduction of greenhouse gases (GHG) emissions and improvement of soil properties. A 90 days' incubation experiment was conducted using treatments which included control (CK), two RBC dosages (1% and 2.5%), and two MRBC doses (1% and 2.5%). Soil physico-chemical and biological properties were monitored to assess the effects due to the treatments. Results showed that both biochars improved soil physicochemical properties as the rate of biochar increased. The higher rates of biochar (RBC_2.5 and MRBC_2.5) particularly increased enzymatic activities (Catalase, Invertase and Urease) in comparison to the control. Data obtained for phospholipid fatty acid (PLFA) concentration indicated an increase in the Gram-negative bacteria (G-), actinomycetes and total PLFA with the increased biochar rate, while Gram-positive bacteria (G+) showed no changes to either level of biochar. As regards fungi concentration, it decreased with the biochar addition, whereas arbuscular mycorrhizal fungi (AMF) showed non-significant changes. The release of CO₂, CH₄ and N₂O showed a decreasing trend over the time. CO₂ cumulative emission decreased for MRBC₁ (5%) and MRBC_2.5 (9%) over the pristine biochar treatments. The cumulative N₂O emission decreased by 15-32% for RBC₁ and RBC_2.5 and by 22-33% for MRBC₁ and MRBC_2.5 as compared to the control, whereas CH₄ emission showed non-significant changes. Overall, the present study provides for the first-time data that could facilitate the correct use of Mg-modified rice biochar as a soil additive for the mitigation of greenhouse gas emission and improvement of soil properties.

Management Strategies to Mitigate N2O Emissions in Agriculture

The concentration of greenhouse gases (GHGs) in the atmosphere has been increasing since the beginning of the industrial revolution. Nitrous oxide (N2O) is one of the mightiest GHGs, and agriculture is one of the main sources of N2O emissions. In this paper, we reviewed the mechanisms triggering N2O emissions and the role of agricultural practices in their mitigation. The amount of N2O produced from the soil through the combined processes of nitrification and denitrification is profoundly influenced by temperature, moisture, carbon, nitrogen and oxygen contents. These factors can be manipulated to a significant extent through field management practices, influencing N2O emission. The relationships between N2O occurrence and factors regulating it are an important premise for devising mitigation strategies. Here, we evaluated various options in the literature and found that N2O emissions can be effectively reduced by intervening on time and through the method of N supply (30–40%, with peaks up to 80%), tillage and irrigation practices (both in non-univocal way), use of amendments, such as biochar and lime (up to 80%), use of slow-release fertilizers and/or nitrification inhibitors (up to 50%), plant treatment with arbuscular mycorrhizal fungi (up to 75%), appropriate crop rotations and schemes (up to 50%), and integrated nutrient management (in a non-univocal way). In conclusion, acting on N supply (fertilizer type, dose, time, method, etc.) is the most straightforward way to achieve significant N2O reductions without compromising crop yields. However, tuning the rest of crop management (tillage, irrigation, rotation, etc.) to principles of good agricultural practices is also advisable, as it can fetch significant N2O abatement vs. the risk of unexpected rise, which can be incurred by unwary management.

Biochar and jasmonic acid application attenuates antioxidative systems and improves growth, physiology, nutrient uptake and productivity of faba bean (Vicia faba L.) irrigated with saline water

The effect of foliar treatment with jasmonic acid at 0.5 mM (JA) and biochar (15 ton ha^-1) as a soil amendment for the faba bean (Vicia faba L. Sakha 4) was studied under salinity conditions. Salt stress led to a significant decrease in leaf numbers, leaf areas and plants, chlorophyll content, relative water content, and yield parameters. In contrast, reactive oxygen species, the proline concentration, level of malondialdehyde, and amount of electrolyte leakage were noticeably increased during both seasons under salt levels of 1500 and 3000 ppm sodium chloride (NaCl). Also, enzyme activities (i.e., of superoxide dismutase, catalase, peroxidase, and glutathione reductase) were increased, especially under a high level of salinity stress (3000 ppm). Application of biochar, jasmonic acid, or biochar + jasmonic acid significantly reduced the catalase, superoxide dismutase, and glutathione reductase activities in salt-stressed plants to values approaching those of the control (unstressed) plants, especially under 1500 ppm of NaCl stress. Biochar and jasmonic acid treatments mitigated the damaging effects of salinity and improved the plant status as indicated by the plant height, leaf area, relative water content, and chlorophyll a and b concentrations. Moreover, biochar and jasmonic acid treatments of the salt-stressed plants enhanced plant productivity, number of flowers, number of seeds per plant, and weight of 100 seeds during two successive seasons. Overall, this study suggests that biochar or jasmonic acid treatments might be promising for mitigating the detrimental impact of salt stress on faba beans.

Biochar decreases methanogenic archaea abundance and methane emissions in a flooded paddy soil

Biochar addition can reduce methane (CH₄) emissions from paddy soils while the mechanisms involved are not entirely clear. Here, we studied the effect of biochar addition on CH₄ emissions, and the abundance and community composition of methanogens and methanotrophs over two rice cultivation seasons. The experiment had the following five treatments: control (CK), chemical fertilizer application only (BC0), and 0.5% (w/w) (BC1), 1% (BC2), and 2% of biochar applied with chemical fertilizers (BC3). The season-wide CH₄ emissions were decreased (P < 0.05) by 22.2-95.7% in biochar application compared with BC0 in the two rice seasons (2017 and 2018). In 2017, biochar application decreased methanogenic archaea (mcrA) but increased methanotrophic bacteria (pmoA) abundances, and decreased the ratio of mcrA/pmoA, as compared with BC0 (P < 0.05). In 2018, the abundance of mcrA was lower in BC2 and BC3 than in BC0 (P < 0.05) but was not different between BC0 and BC1, and the abundance of pmoA was lower in BC1, BC2 and BC3 than in BC0 (P < 0.05). The CH₄ emissions were positively related to abundances of the mcrA gene (P < 0.01) but not to that of the pmoA gene in two rice seasons. Rice grain yield was increased by 62.2-94.1% in biochar addition treatments compared with BC0 in the first year (P < 0.01) and by 29.9-37.6% in BC2 and BC3 compared with BC0 in the second year (P < 0.05). Biochar application decreased CH₄ emissions by reducing methanogenic archaea abundance in the studied flooded paddy soil.

Potential of Novel Biochars Produced from Invasive Aquatic Species Outside Food Chain in Removing Ammonium Nitrogen: Comparison with Conventional Biochars and Clinoptilolite

Previous studies for removal of ammonium from wastewater were mainly conducted using biochars produced from agricultural residue. Feedstock type (agricultural residue, wood, animal waste, and aquatic waste), as well as pyrolysis temperature, can significantly influence biochar properties and hence its adsorption capacity. Such studies are useful in decision making for selecting biochar depending on feedstock availability and pyrolysis temperature. This study aims to explore the effects of different types of biochar (laboratory prepared novel water hyacinth and algae biochar, conventional cedar wood, rice straw, and pig manure biochar) on the adsorption kinetics for ammonium removal from wastewater. The adsorption kinetics of biochars were compared to that of commercially available clinoptilolite and interpreted with their respective physicochemical properties (SEM, FTIR, XRD). Batch tests were performed to evaluate the effects of biochars on adsorption of ammonium nitrogen at different concentrations (10 mg/L and 100 mg/L). The tests reveal that clinoptilolite has the highest adsorption capacity. Among biochars, pig manure (animal based) biochar has a higher adsorption capacity in comparison to conventional agricultural residues based biochars. The capacity of pig manure biochar under highly concentrated ammonium solution (100 mg/L) is merely 20% lower than that of clinoptilolite. Both water hyacinth and algae biochar produced at higher temperature (600 °C) show higher sorption rate and capacity (depending on the initial concentration of ammonium) for ammonium in comparison to that produced at a lower temperature (300 °C). This is likely due to an increase in porosity at higher temperatures of pyrolysis.

Effect of Pyrochar and Hydrochar on Water Evaporation in Clayey Soil under Greenhouse Cultivation

Greenhouse cultivation consumes large volumes of freshwater, and excessive irrigation induces environmental problems, such as nutrient leaching and secondary salinization. Pyrochar (biochar from high-temperature pyrolysis) is an effective soil amendment, and researches have shown that pyrochar application could maintain soil nutrient and enhance carbon sequestration. In addition to pyrochar from pyrolysis, hydrochar from hydrothermic carbonization is considered as a new type of biochar and has the advantages of low energy consumption and a high productive rate. However, the effect of these two biochars on water evaporation in clayey soils under a greenhouse system has seldom been studied. The relationship between water evaporation and biochar properties is still unknown. Thus, in the present study, water evaporation under pyrochar and hydrochar application were recorded. Results showed that both pyrochar and hydrochar application could inhibit water evaporation in clayey soil under greenhouse cultivation. Pyrochar showed a better inhibition effect compared with hydrochar. Correlation analysis indicated that the water evaporation rate was significantly positively correlated with bulk density of biochar (p < 0.05). Overall, application of pyrochar or hydrochar could both reduce soil bulk density and inhibit soil evaporation, and be available for greenhouse cultivation. However, the inhibition effect depends on the properties of the biochar.

Sprinkler Irrigation Is Effective in Reducing Nitrous Oxide Emissions from a Potato Field in an Arid Region: A Two-Year Field Experiment

In arid and semi-arid regions, water-saving irrigation is the primary mode of local agricultural production. Since the chemical fertilizer is the principal source of nitrous oxide (N2O) emissions, we present results from a two-year (2016–2017) field experiment on a potato field to verify the general influence of water-saving irrigation on N2O emissions. A split-plot experiment was established with two irrigation systems and two fertilizer treatments, which give a total of four treatments. Two different irrigation systems were investigated: (i) flood irrigation with nitrogen fertilizer (NF-FI) combined with a control without any fertilizer (C-FI) and (ii) overhead sprinkler irrigation with a nitrogen fertilizer (NF-SI) accompanied with a control without any fertilizer (C-SI). The N2O emissions of the fertilizer treatment were greater than those of the control under each irrigation system. In plots where the fertilizers were applied, using overhead sprinkler irrigation reduced the average cumulative N2O emissions between 40.72% and 59.65% compared with flood irrigation. This was mainly due to the lower amount of water applied and the lower availability of NO3−-N and NH4+-N of soil associated with an overhead sprinkler irrigation. This work shows that the overhead sprinkler irrigation is an effective strategy to use to save water and mitigate emissions of the atmospheric pollutants N2O in comparison to flood irrigation.