Kushal Kumar Baruah

Plant physiological and soil characteristics associated with methane and nitrous oxide emission from rice paddy

Methane (CH4) and nitrous oxide (N2O) are important greenhouse gases causing global warming and climate change. Efforts were made to analyze the CH4 and N2O flux in relation to plant and soil factors from rice (Oryza sativa L.) paddy. Ten popularly grown rice varieties namely Rashmisali, Bogajoha, Basmuthi, Lalkalamdani, Choimora (traditional varieties); Mahsuri, Moniram, Kushal, Gitesh and Profulla (high yielding varieties = HYV) were grown during monsoon season of July 2006. The CH4 and N2O emissions were measured the date of transplanting onwards at weekly interval along with soil and plant parameters. The seasonal integrated CH4 and N2O emission (Esif) from rice ranged from 8.13 g m−2 to 13.00 g m−2 and 121.63 mg N2O-N m−2 to 189.46 mg N2O-N m−2, respectively. Variety Gitesh emitted less N2O and CH4 amongst all the rice varieties. Both CH4 and N2O emission exhibited a significant positive correlation with leaf area, leaf number, tiller number and root dry weight. Soil organic carbon of the experimental field was associated with both CH4 and N2O emission whereas nitrate-N content of soil was associated with N2O emission. Methane emission showed significant positive correlations with soil temperature and crop photosynthetic rate. Traditional rice varieties with profuse vegetative growth recorded higher CH4 and N2O fluxes compared to HYVs. Gitesh and Kushal having low seasonal CH4 and N2O emission with higher yield potential can be recommended as low greenhouse gas emitting rice varieties.

Methane emission associated with anatomical and morphophysiological characteristics of rice (Oryza sativa) plant

Plant-mediated transport is the primary route of methane (CH(4)) emission from the reduced paddy field to the aboveground atmosphere. Experiments were conducted at North Bank Plain Agro-climatic Zone of Assam, India, during monsoon rice-growing season (July to December 2006) to elucidate the influences of anatomical and morphophysiological characteristics of rice (Oryza sativa L.) cultivars on methane emission from submerged agroecosystem. Ten rice cultivars were grown in light-textured loamy soil under rainfed uniform field condition. Among the 10 cultivars, 5 were traditional rice genotypes commonly grown in the agroclimatic zone and the other 5 were improved high-yielding varieties. Wide variation in CH(4) flux was recorded among the rice cultivars, which may be regulated by the difference in anatomical and morphophysiological characteristics of rice plant. Microscopic analysis of stem portion showed that high- and medium-CH(4)-emitting cultivars recorded higher size of the medullary cavity. Leaf area and transpirational rates were also found to be higher in high-CH(4)-emitting varieties. Scanning electron microscopic analysis revealed higher stomatal frequencies in high-methane-emitting cultivars. Data presented in this study suggest that variation in anatomical and morphophysiological characteristics among different rice genotypes may influence CH(4) emission from paddy fields.

Association between contrasting methane emissions of two rice (Oryza sativa L.) cultivars from the irrigated agroecosystem of northeast India and their growth and photosynthetic characteristics

Over two consecutive years in the North Bank Plain Zone of Assam, India, during the spring growing season (February–June) of- 2006 and 2007 we examined effects of morpho-physiological characteristics of rice (Oryza sativa L.) plants in relation to methane (CH4) emission from paddy fields. Traditional cultivar “Agni” and modern improved cultivar “Ranjit” were grown in light textured loamy soil under irrigation. A higher seasonal integrated methane flux (Esif) was recorded from “Agni” compared to “Ranjit”. Both cultivars exhibited an emission peak during active vegetative growth and a second peak at panicle initiation. Leaf and tiller number, leaf area, length, and volume of root were greater in “Agni”, but grain yield and yield-related parameters such as increased photosynthate partitioning to panicles at the expense of roots were greater in “Ranjit”. “Ranjit” also photosynthesed faster than “Agni” during panicle development but slower than “Agni” at tillering. In both the years, a higher soil organic carbon content was recorded in plots of “Agni”. Our results suggest that in “Agni” enhanced diversion of photosynthate to roots resulted in more substrate being available to methanogenic bacteria in the rhizosphere. Additionally, the more extensive vegetative growth of this cultivar may enhance methane transport from the soil to the above-ground atmosphere.

N2O emission in relation to plant and soil properties and yield of rice varieties

Nitrous oxide (N2O) is a major greenhouse gas contributing to global warming. Rainfed rice fields are considered to be a notable source of atmospheric N2O emission. To investigate the dynamics of N2O emission and the relationship of plant and soil properties with emission of N2O in rice, a field experiment was conducted. The five popularly grown rice varieties Luit, Disang, Kapilli, Siana and Phorma were grown in the fall season under rainfed conditions. N2O emission was measured at seven-day intervals starting from the day of transplanting for the whole crop growing season. We also measured soil parameters, e.g. soil pH, soil temperature, soil organic carbon, soil NO3−-N, and field water level; and plant growth parameters: root-shoot dry weight, root length and leaf area. Our results show that N2O emission from the plant varieties ranged from 1.24 μg to 379.40 μg N2O−N m−2 h−1. Seasonal N2O emission from the rice varieties ranged from 77 to 150 mg N2O−N m−2. Root dry weight, shoot dry weight, soil NO3−-N, root length, leaf area and field water showed relationships with N2O emission. Root and shoot weight, soil NO3−-N and field water were found to be the main factors influencing N2O emission. The varieties Phorma and Siana, with lower grain productivity but profuse vegetative growth, showed higher seasonal N2O emission.

A two-year field assessment on the effect of slow release of nitrogenous fertiliser on N2O emissions from a wheat cropping system

Nitrous oxide (N2O) is considered a major contributor to global climate change in addition to carbon dioxide and methane. A significant quantity of N2O emission originates from agriculture, largely from high rates of fertiliser application. We studied N2O emissions from wheat field to evaluate the effect of different forms of fertilisers and the potential for emission reduction. Field experiments were conducted for two consecutive seasons with four fertilisers, namely inorganic fertiliser (NPK), starch-coated urea (SCU), neem-coated urea (NCU), and urea alone (UA) in a tropical wheat ecosystem. Gas samples were collected from the field at weekly intervals using the static chamber technique and analysed with a gas chromatograph. The cumulative N2O emissions were higher from the NPK amended field (3.19kgN2O-Nha–1) followed by UA (3.05kg N2O-N ha–1). The SCU, NCU, and UA amendments decreased the total N2O emissions by 23%, 12%, and 4%, respectively (P<0.05) over the application of NPK. The results indicate a good correlation of N2O emissions with soil organic carbon, soil NO3–-N, NH4+-N, leaf area, and plant biomass. The application of SCU resulted in higher grain productivity and was the most effective substitute for conventional fertiliser in terms of reducing N2O emissions from a tropical wheat ecosystem.

Grain Legumes: Impact on Soil Health and Agroecosystem

Legumes are one of the richest sources of proteins, minerals, and fibers for animals and human being. They also have a great role in maintaining soil fertility through biological nitrogen fixation (BNF). Legumes help in solubilizing insoluble phosphorus (P) in soil, improving the soil physical environment, and increasing soil microbial activity and also have smothering effect on weed. Due to these positive roles in improving soil health and excellent adaptability to marginal environment, legumes are now considered as one of the important components of a cropping system. To reduce poverty, hunger, malnutrition, and environmental degradation, legume crop can be a substitute for cereal crop in marginal lands. Rediscoveries in genetics and genomics now open up new opportunities for improving productivity and quality in grain legume research. The carryover of nitrogen (N) derived from legume grain either in crop senescence or in intercropping system for succeeding crop is important. The necessitate of the interdisciplinary study on grain legumes to address their important role on soil health. Thus, the maximum beneficial effect in modern agriculture as the optimization of fertilizer N use is an essential not only to maintain and restore soil organic carbon (SOC) but also to minimize the nitrate pollution from agricultural source.

Emission estimation of nitrous oxide (N2O) from a wheat cropping system under varying tillage practices and different levels of nitrogen fertiliser

Nitrous oxide is a greenhouse gas with high global warming potential emitted from agricultural sources. The effects of tillage practices and different levels of N fertiliser on seasonal fluxes of N2O were investigated in a field planted with the wheat variety Sonalika. The experiment was conducted during 2012–13 and 2013–14 under conventional tillage (CT) and reduced tillage (RT) farming systems in combination with four different levels of nitrogen fertiliser (i.e. zero nitrogen (F1), 60kgNha–1 (F2), 80kgNha–1 (F3) and 100kgNha–1 (F4)). Both tillage practices and fertiliser significantly (P<0.01) affected seasonal cumulative N2O emissions and wheat yield. However, there was no significant difference in N2O emissions between RTF1 and CTF1 (zero nitrogen). Compared with RT, N2O emission decreased under the CT practice by 2.49%, 10.11%, 7.9% and 27.46% in CTF1, CTF2, CTF3 and CTF4 respectively. Highest and lowest seasonal cumulative fluxes were recorded in RTF4 (N 100kgha–1) and CTF1 (N 0kgha–1) respectively. During the wheat-growing period, nitrogen use efficiency decreased with increasing nitrogen levels and treatment with 60 kg-Nha–1 in the CT practice (CTF2) was found to be effective in increasing nitrogen use efficiency and decreasing yield-scaled N2O emissions.

Response of leaf water status, stomatal characteristics, photosynthesis and yield in black gram and green gram genotypes to soil water deficit

Drought is one of the most important abiotic stresses constraining crop productivity worldwide. The objective of the present study was to investigate the differences in drought tolerance at leaf and stomatal level of black gram (genotypes: T9, KU 301, PU 19, USJD 113) and green gram (genotypes: Pratap, SG 21-5, SGC 16, TMB 37). Drought was applied for fifteen consecutive days at flowering stage (35 days after sowing). Mid-day leaf water potential (ΨL), leaf area, photosynthesis rate (PN), leaf chlorophyll, stomatal conductance (gs) and seed yield of drought- treated plants were calculated relative to those of well watered plants. Stomatal characteristics were observed in terms of stomatal frequency (SF) and stomatal aperture size (SA). Among the studied genotypes, T9 (black gram) and Pratap (green gram) proved their better tolerance capacity to drought by maintaining higher leaf area, ΨL, PN, leaf chlorophyll, gs and SA which contributed to better seed yield. Between the two crops, green gram appeared to be affected to a greater extent, as it experienced higher reduction in yield than black gram. A highly significant positive correlation (level 0.01) of seed yield was obtained with leaf area, ΨL, PN, leaf chlorophyll, gs and SA, whereas SF was found to be poorly correlated with seed yield.

Genotypic variation in carbon fixation, δ13C fractionation and grain yield in seven wheat cultivars grown under well-watered conditions

Biotic carbon (C) sequestration is currently being considered as a viable option for mitigating atmospheric carbon dioxide (CO2) emission, in which photosynthesis plays a significant role. A field experiment was conducted between 2013 and 2015 to investigate the efficiency of seven modern wheat varieties for CO2 fixation, C partitioning, δ13C fractionation in the leaves, and grain yield. A strong correlation between flag leaf photosynthesis and stomatal density (r=0.891) was detected. Photosynthetic efficiency was highest in the variety WH-1021 (28.93µmolm-2s-1). Grain yield was influenced by biomass accumulation in the heads and these were significantly correlated (r=0.530). Our results show that upregulated biomass partitioning to the developing kernels of wheat was inversely proportional to biomass accumulation in the roots, and led to a higher grain yield. These results led us to conclude that identification of a wheat genotype like WH-1021 followed by WH-1080 and WH-711, with higher isotopic discrimination in the flag leaves, stomatal densities, water use and photosynthetic efficiencies along with higher grain yield, can contribute to sustainable agriculture in future climate change situation in India. A yield increment of 9-48% was recorded in WH-1021 over other six tested wheat varieties.

Potential option for mitigating methane emission from tropical paddy rice through selection of suitable rice varieties

Abstract. Cultivation of rice, a globally important cereal crop, is a major cause of emission of the greenhouse gas (GHG) methane (CH4), giving rise to global warming. Physiological and anatomical characteristics of rice plants associated with CH4 emission were studied in six high-yielding rice varieties, Dikhow, Dishang, Jaya, Kolong, Kopilee and Lachit, during the pre-monsoon season (April–August) for 2 years (2013 and 2014) in a tropical climate in India. Significant differences (P < 0.001) in photosynthetic rate among the rice varieties were recorded and were found to influence CH4 emission from the ecosystem. Rate of CH4 emission was found correlated (r = 0.942) with size of the xylem vessels of the node of the varieties. Kolong, Lachit and Dikhow were identified as low CH4 emitters with smaller xylem vessels. The recorded GHG intensity (GHGI) revealed rice varieties as a source of GHGs, and among the varieties, Kopilee as a major source of CH4, with GHGI of 0.083 and 0.093 during 2013 and 2014, respectively. Results suggest that selection of suitable rice varieties with high grain yield accompanied by lower rate of CH4 emission can be a viable option for reduction of CH4 emissions from rice agriculture.