Impact of elevated CO<Subscript>2</Subscript>, flooding,and temperature interaction on heterotrophic nitrogen fixation in tropical rice soils

Response of N₂ fixation to elevated CO₂ would be modified by changes in temperature and soil moisture because CO₂ and temperature or water availability has generally opposing effects on N₂ fixation. In this study, we assessed the impacts of elevated CO₂ and temperature interactions on nitrogenase activities, readily mineralizable C (RMC), readily available N (NRN) contents in an alluvial and a laterite rice soil of tropical origin. Soil samples were incubated at ambient (370 μmol mol^-1) and elevated (600 μmol mol^-1) CO₂ concentration at 25oC, 35oC, and 45oC under non-flooded and flooded conditions for 60 days. Elevated CO₂ significantly increased nitrogenase activities and readily mineralizable C in both alluvial and laterite soils. All these activities were further stimulated at higher temperatures. Increases in nitrogenase activity as a result of CO₂ enrichment effect over control were 16.2%, 31.2%, and 66.4% and those of NRN content were 2.0%, 1.8%, and 0.5% at 25oC, 35oC and 45oC, respectively. Increases in RMC contents were 7.7%, 10.0%, and 10.6% at 25°C, 35°C and 45°C, respectively. Soil flooding resulted in a more clear impact of CO₂ enrichment than the non-flooded soil. The results suggest that in tropical rice soils, elevated CO₂ increased readily available C content in the soil, which probably stimulates growth of diazotrophic bacteria with enhanced N₂ fixation and thereby higher available N.     

Evaluation of MSW Compost as a Component of Integrated Nutrient Management in Wetland Rice

The potential of municipal solid waste compost (MSWC) was evaluated for rice cultivar, IET- 1444, during the wet seasons of 1997-99. Field experiments were conducted at the Agriculture Experimental Farm of Calcutta University, West Bengal, India using MSWC and cow dung manure (CDM), with or without urea (U), and fertilizers (F). Dry matter accumulation was highest with CDM + U, followed, in a descending order, by MSWC + U and F. Panicle length was largest and thousand–grain-weight were highest for F. Application of CDM alone gave 30% higher grain yield over MSWC but the latter, along with urea, increased grain yield by 49% over MSWC alone. Uptake of N by straw and grain was significantly higher with CDM as compared to MSWC. Percent N recovery was higher when fertilizer in the form of urea was applied with either CDM or MSWC. Uptake of heavy metals (Zn, Cu, and Pb) by straw and grain of rice was lower with the application of MSWC alone than with the other treatments except control. Uptake of Cd was below detection limit. There was no significant variation between the physico-chemical properties of soil due to the application of these treatments. Results indicated that MSWC application to rice was effective and safe to be used as an alternative organic supplement.     

Effect of MSW Compost on Microbiological and Biochemical Soil Quality Indicators

This laboratory incubation study was conducted to evaluate the effect of municipal solid waste compost (MSWC) as a soil amendment on soil quality indicators, such as microbial biomass, and their activities. The MSWC was compared against cow dung manure (CDM), a traditional organic supplement. The comparative study was carried out in water regimes of 60% water holding capacity (WH) of soil and under waterlogged (WL) condition. MSWC was applied to an alluvial soil (Typic Fluvaquent) at the rates of 0, 2.5, 10, 20 and 40 and CDM at 0, 20 and 40 t/ha. Microbial biomass-C (MBC), glucose induced soil respiration (SR), urease and acid phosphatase activities in soil were analyzed following 15, 30, 45, 60, 90 and 120 days of incubation. The parameters studied were significantly higher in CDM-treated than in MSWC-treated soils. Increase in graded doses of MSWC from 2.5 to 40 t/ha substantially increased the MBC, SR, urease and phosphatase activities in the soil. In 60% WH regime, MBC and SR increased for the first 30 days of incubation and then declined. Under the WL regime, the MBC declined while SR increased from 15 days till 120 days of incubation. Urease and phosphatase activities of soil increased for up to 60 days during incubation in 60% WH regime and then decreased. Activities of both the enzymes under WL regime decreased progressively during incubation. There were no negative impacts on the soil quality indicators from high application rates of MSWC.     

Impact of nitrogen fertilization and tillage practices on nitrous oxide emission from a summer rice ecosystem

ABSTRACT

Identification of the combination of tillage and N fertilization practices that reduce agricultural Nitrous oxide (N₂O) emissions while maintaining productivity is strongly required in the Indian subcontinent. This study investigated the effects of tillage in combination with different levels of nitrogen fertilizer on N₂O emissions from a rice paddy for two consecutive seasons (2013–2014 and 2014–2015). The experiment consisted of two tillage practices, i.e., conventional (CT) and reduced tillage (RT), and four levels of nitrogen fertilizer, i.e., 0 kg N ha^–1 (F1), 45 kg N ha^–1 (F2), 60 kg N ha^–1 (F3) and 75 kg N ha^–1 (F4). Both tillage and fertilizer rate significantly affected cumulative N₂O emissions (p < 0.05). Fertilizer at 45 and 60 kg N ha^–1 in RT resulted in higher N₂O emissions over than did the CT. Compared with the recommended level of 60 kg N ha^?1, a 25% reduction in the fertilizer to 45 kg N ha^?1 in both CT and RT increased nitrogen use efficiency (NUE) and maintained grain yield, resulting in the lowest yield-scaled N₂O-N emission. The application of 45 kg N ha^?1 reduced the cumulative emission by 6.08% and 6% in CT and RT practices, respectively, without compromising productivity.     

Effect of Flue Gas Treatment on the Solubility and Fractionation of Different Metals in Fly Ash of Powder River Basin Coal

Studies were conducted to examine the effect of flue gas carbon dioxide (CO₂) on solubility and availability of different metals in fly ash of Powder River Basin (PRB) coal, Wyoming, USA. Initial fly ash (control) was alkaline and contains large amounts of water-soluble and exchangeable metals. Reaction of flue gas CO₂ with alkaline fly ash resulted in the formation of carbonates which minimized the solubility of metals. Results for metal fractionation studies also supported this fact. The present study also suggested that most of the water-soluble and exchangeable metals present in the control (untreated) fly ash samples decreased in the flue gas-treated samples. This may be due to the transfer of the above two forms to more resistant forms like carbonate bound (CBD), oxide bound (OXD), and residual (RS). Geochemical modeling (Visual MINTEQ) of water solubility data suggested that the saturation index (SI) values of dolomite (CaMg(CO₃)₂) and calcite (CaCO₃) were oversaturated, which has potential to mineralize atmospheric CO₂ and thereby reduce leaching of toxic metals from fly ash. Results from this study also showed that the reaction of flue gas CO₂ with alkaline fly ash not only control the solubility of toxic metals but also form carbonate minerals which have the potential to fix CO₂.     

Uses,values, and use values of the Sundarbans

The decimation of the Sundarbans has resulted from attempts to satisfy short-term demands by exhausting the chances of satisfying future demands. The forest cannot be preserved by a policy that under-valorizes the urgency of the short-term needs or by a policy that is imposed from above, but it may be by social forestry. Social forestry augments the supply of forest products from non-forest lands, and, most significantly, includes the users in developing appropriate forest policies.     

Feeding deterrents forphilosamia ricini (samia cynthia subsp.Ricini) fromtithonia diversifolia

Tagitinin A and C and hispidulin isolated fromTithonia diversifolia (Hemsl.) Gray, were potent feeding deterrents, when evaluated against 4th instar caterpillars of the Eri-silkworm(Philosamia ricini Hutt.) (Lepidoptera: Saturniidae); tagitinin F was not.