Evaluating changes in cellulolytic bacterial population to explain methane emissions from air-dried and composted manure treated rice paddy soils

The impact of organic fertilizer replacement on greenhouse gas emissions and its influencing factors

Although organic fertilizers played an important role in enhancing crop yield and soil quality, the effects of organic fertilizers replacing chemical fertilizers on greenhouse gas (GHG) emissions remained inconsistent, and further impeding the widespread adoption of organic fertilizers. Therefore, a global meta-analysis used 568 comparisons from 137 publications was conducted to evaluate the responses of GHG emissions to organic fertilizers replacing chemical fertilizers. The results indicated that organic fertilizers replacing chemical fertilizers significantly decreased N2O emissions, but increasing global warming potential (GWP) by enhancing CH4 and CO2 emissions. When replacing chemical fertilizers with organic fertilizers, a variety of factors such as climate conditions, soil conditions, crop types and agricultural practices influenced the GHG emissions and GWP. Among these factors, fertilizer organic C and available N level were the main factors affecting GHG and GWP. However, considering the feasibility and ease of optimizing these factors, fertilizer organic C, C/N and N substitution rate showed a more favorable choice for GWP reduction, and their interactions significantly affecting GWP. Moreover, considering the distinct GHG emissions patterns in dryland and paddy field, the analysis of optimizing GWP based on fertilizer organic C, C/N and N substitution rate was separately conducted. According to the simulation optimization, the optimal combination of fertilizer organic C (137.2-228.8 g·kg-1), C/N (6.9-52.0) and N substitution rate (20.0-22.5 %) effectively suppressed the extent of increase in GWP in paddy field compared with chemical fertilizers. In dryland, optimizing fertilizer organic C (100-278 g·kg-1), C/N (70.7-76.6) and N substitution rate (10.2-16.0 %) led to a reduction in GWP compared with chemical fertilizers, indicating that dryland are more suitable for promoting organic fertilizer application. In conclusion, this meta-analysis study quantitatively assessed the GHG emissions when organic fertilizers replacing chemical fertilizers, and also provided a scientific basis for the mitigation of GHG emissions by organic fertilizers management.

Assimilating atmospheric carbon dioxide in tea gardens of northeast India

Carbon dioxide (CO₂) is the most important greenhouse gas in the atmosphere and phyto-assimilation is the most effective technique to mitigate global warming effect of CO₂ gas in the atmosphere. Tea is an evergreen perennial plant and cultivated worldwide under subtropical humid climatic condition for harvesting its tender shoots. Tea bushes of different cultivars and ages are grown in combination to minimize possible adverse effect of biotic and abiotic stresses; hence distribution of tea plantation in a tea garden is complex in nature. Large shade trees are also an integral part of tea garden. Those plantations in tea garden have huge potential to capture atmospheric CO₂; however, ability of tea bushes to mitigate global warming while producing tea shoots is not quantified before. The objective of this study was to quantify the potential of tea plantation to mitigate greenhouse effect (global warming mitigation potential, GWMP) due to assimilation of atmospheric CO₂ gas. High yielding TV23 cultivar assimilated significantly higher amount of CO₂ as compared to quality tea producing cultivars (S3A/3) and mature 25-30 years old tea bushes absorb more CO₂ from the atmosphere as compared to younger tea bushes. Considering the mixed population of cultivars in tea gardens, overall, tea bushes sequestrated 5134.4 ± 831.6 kg CO₂ ha^-1 yr^-1 in their biomass and had GWMP 3.47 ± 0.64 kg CO₂ KMTH^-1 yr^-1. Shade trees sequestrated 4037.4 ± 589.9 kg CO₂ ha yr^-1 from the atmosphere. Hence, the GWMP of whole plantation ((both tea bushes and shade trees) was 6.19 ± 1.7 kg CO₂ KMTH^-1 yr^-1. In this study, tea bushes sequestrated 52.7-61.3% of the total CO₂ sequestrated by the plantations in tea garden. This study enabled to understand that tea bushes play significant role in mitigating global warming by assimilating and sequestrating atmospheric CO₂ and the estimated value of global warming mitigation potential may be used for direct estimation of C sequestration by plantations in tea garden using its productivity value.

Effects of different fertilizers on methane emissions and methanogenic community structures in paddy rhizosphere soil

Paddy soil accounts for 10% of global atmospheric methane (CH₄) emissions. Many types of fertilizers may enhance CH₄ emissions, especially organic fertilizer. The aim of this study was to explore the effects of different fertilizers on CH₄ and methanogen patterns in paddy soil. This experiment involved four treatments: chemical fertilizer (CT), organic fertilizer (OT), mixed with chemical and organic fertilizer (MT), and no fertilizer (ctrl). The three fertilization treatments were applied with total nitrogen at the same rate of 300 kg N ha^-1. Paddy CH₄, soil physicochemical variables and methanogen communities were quantitatively analyzed. Rhizosphere soil mcrA and pmoA gene copy numbers were determined by qPCR. Methanogenic 16S rRNA genes were identified by MiSeq sequencing. The results indicated CH₄ emissions were significantly higher in OT (145.31 kg ha^-1) than MT (84.62 kg ha^-1), CT (77.88 kg ha^-1) or ctrl (32.19 kg ha^-1). Soil organic acids were also increased by organic fertilization. CH₄ effluxes were significantly and negatively related to mcrA and pmoA gene copy numbers, and positively related to mcrA/pmoA. Above all, hydrogenotrophic Methanocella and acetoclastic Methanosaeta were the predominant methanogenic communities; these communities were strictly associated with soil potassium, oxalate, acetate, and succinate. Application of organic fertilizer promoted the dominant acetoclastic methanogens, but suppressed the dominant hydrogenotrophic methanogens. The transformation in methanogenic community structure and enhanced availability of C substrates may explain the increased CH₄ production in OT compared to other treatments. Compared to OT, MT may partially mitigate CH₄ emissions while guaranteeing a high rice yield. On this basis, we recommend the local fertilization pattern should change from 300 N kg ha^-1 of organic manure to the same level of mixed fertilization. Moreover, we suggest multiple combinations of mixed fertilization merit more investigation in the future.

Beneficial effect of compost utilization on reducing greenhouse gas emissions in a rice cultivation system through the overall management chain

Livestock manure application can stimulate greenhouse gas (GHG) emissions, especially methane (CH₄) in rice paddy. The stabilized organic matter (OM) is recommended to suppress CH₄ emission without counting the additional GHG emission during the composting process. To evaluate the effect of compost utilization on the net global warming potential (GWP) of a rice cropping system, the fluxes of GHGs from composting to land application were calculated by a life cycle assessment (LCA) method. The model framework was composed of GHG fluxes from industrial activities and biogenic GHG fluxes from the composting and rice cultivation processes. Fresh manure emitted 30MgCO₂-eq.ha^-1, 90% and 10% of which were contributed by CH₄ and nitrous oxide (N₂O) fluxes, respectively, during rice cultivation. Compost utilization decreased net GWP by 25% over that of the fresh manure during the whole process. The composting process increased the GWP of the industrial processes by 35%, but the 60% reduction in CH₄ emissions from the rice paddy mainly influenced the reduction of GWP during the overall process. Therefore, compost application could be a good management strategy to reduce GHG emissions from rice paddy systems.

Methane production, oxidation and mitigation: A mechanistic understanding and comprehensive evaluation of influencing factors

Methane is one of the critical greenhouse gases, which absorb long wavelength radiation, affects the chemistry of atmosphere and contributes to global climate change. Rice ecosystem is one of the major anthropogenic sources of methane. The anaerobic waterlogged soil in rice field provides an ideal environment to methanogens for methanogenesis. However, the rate of methanogenesis differs according to rice cultivation regions due to a number of biological, environmental and physical factors like carbon sources, pH, Eh, temperature etc. The interplay between the different conditions and factors may also convert the rice fields into sink from source temporarily. Mechanistic understanding and comprehensive evaluation of these variations and responsible factors are urgently required for designing new mitigation options and evaluation of reported option in different climatic conditions. The objective of this review paper is to develop conclusive understanding on the methane production, oxidation, and emission and methane measurement techniques from rice field along with its mitigation/abatement mechanism to explore the possible reduction techniques from rice ecosystem.