Greenhouse gas emission from rice fields: a review from Indian context.

Agricultural soil acts as a source and sink of important greenhouse gases (GHGs) like methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). Rice paddies have been a major concern to scientific community, because they produce the threatening and long-lasting GHGs mainly CH4 and N2O. Around 30% and 11% of global agricultural CH4 and N2O, respectively, emitted from rice fields. Thus, it is urgent to concurrently quantify the fluxes of CH4 and N2O to improve understanding of both the gases from rice fields and to develop mitigation strategies for upcoming climate change reduction. An effort is being made in this review to discuss exclusively the emission of CH4 and N2O under normal and controlled conditions in different locations of India and also addresses the current synthesis of available data on how field and crop management activities influence CH4 and N2O emissions in rice fields. Making changes to conventional crop management regimes could have a significant impact on reducing GHG emissions from rice field. Environmental and agricultural factors related to soil could be easily altered by management practices. So, knowing the mechanism of CH4 and N2O production and release in the rice field and factors controlling the emissions is fundamental to develop well-organized strategies to reduce emissions from rice cultivated soil. This will help the regulatory bodies or policy makers to formulate adequate policies for agricultural farmers to refine the GHG emissions as well as minimize the global climate change.

Fertilizer management through coated urea to mitigate greenhouse gas (N2O) emission and improve soil quality in agroclimatic zone of Northeast India.

Agricultural soils are an important source of greenhouse gas nitrous oxide (N2O) emission. The comprehensive effects of nitrogen fertilizer management on N2O emission from paddy fields of India have not been evaluated under field conditions. A 2-year field study was conducted to evaluate the effect of different nitrogen fertilizers, namely, conventional fertilizer (NPK), starch-coated urea (SCU), neem-coated urea (NCU), and normal urea alone (NUA) on soil quality, grain yield, and N2O emission from rice field. Gas samples were collected from the field at weekly intervals by static chamber technique and analyzed in a gas chromatograph. During the crop-growing season, the application of NPK resulted in the highest cumulative N2O emission (2.49 kg N2O-N ha-1) followed by NUA (2.34 kg N2O-N ha-1), NCU (2.20 kg N2O-N ha-1), and SCU (1.97 kg N2O-N ha-1). As against the application of conventional fertilizer (NPK), the application of SCU and NCU reduced the total N2O emission by 21% and 12%, respectively (p < 0.05), during the rice-growing period. The results indicate a good correlation of N2O emissions with soil organic carbon, soil mineral nitrogen, and urease activity (p < 0.05) at different stages of crop growth. Application of SCU significantly increased the rice grain productivity by 12%, 10%, and 3% over NPK (control), NCU, and NUA respectively without affecting the soil quality and nutrient status. The use of SCU improved the nitrogen use efficiency (NUE) and was the effective substitute for conventional fertilizer in terms of reducing N2O emissions from tropical rice paddy.

Sorption of volatile organic compounds on non-activated biochar.

This work dealt with the determination of the suitability of sorption of Volatile Organic Compounds (VOCs) on biochars prepared from neem, sugarcane and bamboo feedstocks. Six different VOCs namely benzene, toluene, methyl chloride, xylene, chloroform and carbon tetrachloride were used in a laboratory-scale set-up on non-activated biochars prepared via slow pyrolysis (350-550 °C). Although all the chars showed considerable sorption but amongst them N3 (neem-based biochar) showed the maximum removal efficiency (65.5 mg g-1 for toluene). Variation in pyrolysis temperature and feedstock type showed significant change in the porosity and specific surface area of the biochar, which is favorable for VOC sorption efficiency. With higher surface area and contact time, the sorption capacity of char enhanced. However, the extent of sorption capacity of biochars differed with changing VOC type. Pseudo-Second-Order model fitted well with the results obtained from VOC sorption kinetics.

Effect of foliar application of plant growth regulators on nitrous oxide (N2O) emission and grain yield in wheat.

Agricultural soils are the major source of global nitrous oxide (N2O) emission, and more than two thirds of N2O emission originate from soil. Recent studies have identified that green plants contribute to transport of N2O to the atmosphere. We investigated the effects of foliar application of plant growth regulators (PGRs) and growth stimulating chemicals on N2O emission and wheat grain yield for 2 years. The PGRs' abscisic acid (ABA) and cytozyme (20 mg L-1), kinetin (10 and 20 mg L-1) and wet tea extract (1:20 w/w) along with distilled water as control were sprayed on wheat canopy at the tillering and panicle initiation stages. Our results showed that cytozyme and tea extract enhanced the plant dry biomass over control. Kinetin (10 and 20 mg L-1) and cytozyme increased the plant photosynthetic rate and photosynthate partitioning towards the developing grain. ABA (20 mg L-1) and kinetin (10 and 20 mg L-1) reduced the N2O emission over control primarily through regulation of leaf growth, stomatal density and xylem vessel size. Leaf area, stomatal density and xylem vessel size were found to be associated with N2O transport and emission. We concluded that use of ABA and kinetin can reduce N2O emissions without any impact on wheat grain yield.