Sudip Mitra

Methane emissions from irrigated rice fields in northern India (New Delhi)

Methane (CH4) emission fluxes from rice fields as affected by water regime, organic amendment, and rice cultivar were measured at the Indian Agricultural Research Institute, New Delhi, using manual and automatic sampling techniques of the closed chamber method. Measurements were conducted during four consecutive cropping seasons (July to October) from 1994 to 1997. Emission rates were very low (between 16 and 40 kg CH4 m−2 season−1) when the field was flooded permanently. These low emissions were indirectly caused by the high percolation rates of the soil; frequent water replenishment resulted in constant inflow of oxygen in the soil. The local practice of intermittent flooding, which encompasses short periods without standing water in the field, further reduced emission rates. Over the course of four seasons, the total CH4 emission from intermittently irrigated fields was found to be 22% lower as compared with continuous flooding. The CH4 flux was invariably affected by rice cultivar. The experiments conducted during 1995 with one cultivar developed by IRRI (IR72) and two local cultivars (Pusa 169 and Pusa Basmati) showed that the average CH4 flux from the intermittently irrigated plots without any organic amendment ranged between 10.2 and 14.2 mg m−2 d−1. The impact of organic manure was tested in 1996 and 1997 with varieties IR72 and Pusa 169. Application of organic manure (FYM + wheat straw) in combination with urea (1:1 N basis) enhanced CH4 emission by 12–20% as compared with fields treated with urea only. The site in New Delhi represents one example of very low CH4 emissions from rice fields. Emissions from other sites in northern India may be higher than those in New Delhi, but they are still lower than in other rice-growing regions in India. The practice of intermittent irrigation--in combination with low organic inputs--is commonly found in northern India and will virtually impede further mitigation of CH4 emissions in significant quantities. In turn, the results of this study may provide clues to reduce emissions in other parts of India with higher baseline emissions.

Properties of rice soils affecting methane production potentials: 1. Temporal patterns and diagnostic procedures

Thirty-one rice soils from different locations in the Philippines were incubated anaerobically for 100 d to determine methane (CH4) production potentials and to establish relationships between physico-chemical properties of soil and CH4 production potential. These soils showed pronounced variations in pattern and magnitude of CH4 production. Total CH4 production over 100 d incubation ranged from 163 to 837 μg CH4 g−1 soil. Total N, soil texture (clay and sand fractions mainly) and cation exchange capacity (CEC) of the soils had significant effect on CH4 production potential. Available K and active Fe content also affected the CH4 production potentials of various soils. An assessment of CH4 production with high accuracy could be obtained from soil redox potential (Eh) development during incubation; the difference between initial and equilibrium Eh allowed a computation of CH4 production with more than 70% reliability. The CH4 production potentials obtained over long incubation periods could be assessed, with reasonable accuracy, by a relatively short incubation experiments and fewer measurements of CH4 production. Only three samplings of CH4 production rate within a short incubation period of 37 d facilitated a prediction of total CH4 production over 100 d incubation using the following algorithm:P0-100=99.21+10.79X4+11.69X16+45.79X37 (R2=0.91; P<0.01),where P0-100 is the total CH4 production during 100 d of incubation and Xn is CH4 production rate at n days of incubation. Longer incubation periods (86 d) were required to achieve a reliability of more than 95%.

Tillage and crop residue management methods had minor effects on the stock and stabilization of topsoil carbon in a 30-year field experiment

We studied the effects of tillage and straw management on soil aggregation and soil carbon sequestration in a 30-year split-plot experiment on clay soil in southern Finland. The experimental plots were under conventional or reduced tillage with straw retained, removed or burnt. Wet sieving was done to study organic carbon and soil composition divided in four fractions: 1) large macroaggregates, 2) small macroaggregates, 3) microaggregates and 4) silt and clay. To further estimate the stability of carbon in the soil, coarse particulate organic matter, microaggregates and silt and clay were isolated from the macroaggregates. Total carbon stock in the topsoil (equivalent to 200 kg m(-2)) was slightly lower under reduced tillage (5.0 kg m(-2)) than under conventional tillage (5.2 kg m(-2)). Reduced tillage changed the soil composition by increasing the percentage of macroaggregates and decreasing the percentage of microaggregates. There was no evidence of differences in the composition of the macroaggregates or carbon content in the macroaggregate-occluded fractions. However, due to the higher total amount of macroaggregates in the soil, more carbon was bound to the macroaggregate-occluded microaggregates in reduced tillage. Compared with plowed soil, the density of deep burrowing earthworms (Lumbricus terrestris) was considerably higher under reduced tillage and positively associated with the percentage of large macroaggregates. The total amount of microbial biomass carbon did not differ between the treatments. Straw management did not have discernible effects either on soil aggregation or soil carbon stock. We conclude that although reduced tillage can improve clay soil structure, generally the chances to increase topsoil carbon sequestration by reduced tillage or straw management practices appear limited in cereal monoculture systems of the boreal region. This may be related to the already high C content of soils, the precipitation level favoring decomposition and aggregate turnover in the winter with topsoil frost.

Properties of rice soils affecting methane production potentials: 2. Differences in topsoil and subsoil

Methane (CH4) is one of the important greenhouse gases accounting for 15% of the total enhanced greenhouse effect. A laboratory experiment was conducted with nine soils from the Philippines and two soils from India to determine the CH4 production potential of topsoil and subsoil, and to assess the role of different fractions of soil organic C in influencing CH4 production potential. CH4 production potentials of topsoils varied in a wide range from 20 μg g−1 soil (Urdaneta soil) to 837 μg g−1 soil (Pila soil) over 100 d of incubation. In contrast, CH4 production potentials of subsoils were low (< 2 μg g−1 soil over 100 d of incubation). The topsoil was the main source of CH4 in the flooded rice soils contributing 99.95% to the total CH4 production while the subsoil contributed negligibly (0.05%). CH4 production potentials of the topsoils showed significant correlation with cation exchange capacity (CEC), total N and available K contents of soils. For the subsoils, CH4 production potentials had a significant correlation with available P and clay contents of the soils. Considering the differences in all the soil properties and the CH4 production potentials between topsoils and subsoils, a significant relationship of CH4 production potential with CEC, available K and enriched C (extra C content of topsoil compared to that of subsoil) was obtained. Two carbon fractions, water soluble C (H2O-C) and carbon mineralised under anaerobic conditions (AnMC) affected total CH4 production indirectly rather than directly.

Genetic diversity in ecotypes of the scarce wild medicinal crop Zingiber moran revealed by ISSR and AFLP marker analysis and chromosome number assessment

Zingiber moran, a rare ginger found only in a few parts of northeast India, faces the threat of extinction due to its exploitation as an important medicinal plant. In this study, the chromosome number of wild ecotypes of Z. moran was determined and the genetic analysis was carried out using two kinds of molecular markers: inter simple sequence repeats (ISSR) and amplified fragment length polymorphism (AFLP). A chromosome number of 2n = 22 was confirmed for all 10 ecotypes investigated. AFLP analysis revealed a greater amount of genetic polymorphism (95.06%), with a strong resolving power in detecting intraspecific variation, compared to ISSR analysis (34.61%). Genetic diversity parameters, such as number of observed alleles (na), mean number of effective alleles (ne), mean Neis gene diversity index (h), and Shannon index (I) for ISSR and AFLP were in the range 1.34–1.95, 1.25–1.60, 1.44–0.33, and 0.20–0.49, respectively. Marker indices and polymorphic information content varied from 0.5–19.3 and 0.03–0.27 for ISSR, and 28.2–39 and 0.3–0.39 for AFLP, respectively. Dendrograms derived by unweighted pair group method of arithmetic averages cluster analysis based on molecular data classified the ecotypes into two major clusters. The Mantel test cophenetic correlation coefficient (r) for ISSR (0.85) and AFLP (0.91) showed a good degree of confidence in the association with 10 ecotypes. Clustering was further supported by principle component analysis which demarcated individuals of hilly topography from the ones of plain land.

Genetic diversity and relationship of Hedychium from Northeast India as dissected using PCA analysis and hierarchical clustering

Molecular genetic fingerprints of eleven Hedychium species from Northeast India were developed using PCR based markers. Fifteen inter-simple sequence repeats (ISSRs) and five amplified fragment length polymorphism (AFLP) primers produced 547 polymorphic fragments. Positive correlation (r = 0.46) was observed between the mean genetic similarity and genetic diversity parameters at the inter-species level. AFLP and ISSR markers were able to group the species according to its altitude and intensity of flower aroma. Cophenetic correlation coefficients between the dendrogram and the original similarity matrix were significant for ISSR (r = 0.89) compared to AFLP (r = 0.83) markers. This genetic characterization of Hedychium from Northeast India contributes to the knowledge of genetic structure of the species and can be used to define strategies for their conservation and management.

Exploration of ‘Hot-Spots’ of Methane and Nitrous Oxide Emission from the Agriculture Fields of Assam, India

BackgroundAgricultural soils contribute towards the emission of CH4 (mainly from paddy fields) and N2O (from N-fertilizer application), the two important greenhouse gases causing global warming. Most studies had developed the inventories of CH4 and N2O emission at the country level (larger scale) for India, but not many studies are available at the local scale (e.g. district level) on these greenhouse gases (GHGs). Assam is an important state in the North Eastern region of India. In addition to being the regional economic hub for the entire region, agriculture is the major contributor to the state’s gross domestic product. In Assam about three-fourths of the area is under paddy cultivation and rice is the staple food. With this background, a district wise inventory of CH4 and N2O emission in the North Eastern state of Assam, India was carried out using different emission factors, viz., IPCC, Indian factors and others, to highlight the discrepancies that arose in the emission estimation of these important GHGs while used at the smaller scale i.e. district level. This study emphasizes the need for better methodologies at the local level for GHGs inventories. This study also reiterates the fact that no emission factor is universally applicable across all regions. The GHGs like CH4 and N2O are highly site and crop specific and the factors required for their inventory are driven by cultural practices, agronomic management, soil resources and socio-economic drivers.Material and methodsIn this study, Intergovernmental Panel on Climate Change (IPCC) methodology was used for the estimation of CH4 and N2O emission. In case of N2O emission, both direct and indirect emission from agricultural soil was estimated for the various districts of Assam.ResultsThe CH4 (base year 2000–2001) and N2O (base year 2001–2002) emission was estimated to be 121 Gg and 1.36 Gg from rice paddy and agricultural fields of Assam state respectively.ConclusionsThis study is the first report on the estimation of the GHG emission at the district level from the entire state of Assam, agriculturally one very important state of North Eastern India. This state is also considered as remote due to its geographical location. The study clearly elucidates that there is large variation in the emission inventory of CH4 and N2O at the district level (local scale) when different emission factors are used. This calls for detailed and comprehensive data collection and mapping at the micro level for accurate inventory of greenhouse gases in future from agriculture fields.

Greenhouse Gases Emission from Rice Paddy Ecosystem and their Management

Various research works across the globe have shown that climate change impacts the agriculture differently at different locations. It is also true that agriculture affects climate quite significantly. Emission of Greenhouse gases (GHGs) from rice paddy system is one of the important examples of agriculture’s impact on climate system. Intensive research on this topic in the last few decades has provided various mitigative options. While some of these options are readily implementable, some other options have been successful only at the laboratory level. Yet some other options, of the nature of ‘farming practices’, are well understood and have been adopted in many parts of the world. However, the plant development path of mitigating GHGs from agricultural cropping systems has not yet been well established. As such, more aggressive research strategies and field validations are needed for establishing ‘plant development’ as a sustainable tool for GHG mitigation in agriculture sector.

Impact of Tillage and Residue Management Practices on Soil Aggregates and Soil Organic Carbon

Soil organic matter and soil aggregate stability are good indicators of soil quality and both can be positively affected by reduced tillage and residue management practices. A field study was conducted to find the impacts of tillage and residue management practices on soil carbon stock and distribution of SOC within different soil physical fractions. The study site was a 30-year experiment divided to six treatment classes, conventional tillage (CT) and reduced tillage (RT) with straw incorporated (S), straw removed (SR) and straw burned (SB). The soil was segregated into four different classes: large and small macroaggregates, microaggregates and silt and clay which were analyzed for total carbon. Reduced tillage or residue incorporation did not result in higher C sequestration but there were more water stable aggregates in the reduced tillage treatment.