Long-term trends of direct nitrous oxide emission from fuel combustion in South Asia

An increasing concentration of nitrous oxide (N2O) in the global atmosphere can perturb the ecological balance, affecting the climate and human life. South Asia, one of the world's most populous regions, is a hotspot for N2O emission. Although agriculture traditionally dominated the region, economic activities are rapidly shifting towards industry and energy services. These activites may become the largest emitters of N2O in future. Yet, few attempts have been made to estimate long-term direct N2O emission from fuel combustion for the different energy-consuming sectors in the South Asian region. Therefore, the present study developed a comprehensive sectoral N2O emission inventory for South Asian countries for the time period of 1990–2017, with projections till 2041. It revealed that the average N2O emission from fuel combustion in the South Asia region is about 40.96 Gg yr−1 with a possible uncertainty of ±12 Gg yr−1, showing an increase of more than 100% from 1990 to 2017. Although India is the major contributor, with an average of 34 Gg yr−1 of N2O emissions, in terms of growth, small countries like Bhutan and Maldives are dominating other South Asian countries. Sector-wise, the residential sector contributed a maximum emission of 14.52 Gg yr−1 of N2O but this is projected to reduce by more than 50% by 2041. This is because of the successful promotion of cleaner fuels like liquefied petroleum gas over more polluting fuelwood. Power generation contributed 9.43 Gg yr−1of N2O emissions, exhibiting a maximum growth of 395%, followed by road transport (289%) and industry (231%). Future N2O emissions from transport, power and industry are projected to rise by 2.8, 3.3, and 23.9 times their 2017 estimates, respectively, due to the incapability of current policies to combat rising fossil fuel consumption. Mitigation options, such as replacing diesel and compressed natural gas vehicles with electricity-driven vehicles, can decelerate N2O emissions to 45% by 2041 for road transport. A 41% reduction is possible by displacing coal with renewables in the power and industry sectors. Overall, the South Asian contribution to global N2O emissions has enlarged from 2.7% in 1990 to 5.7% in 2007–2016, meaning there is an urgent need for N2O emission mitigation in the region

Water-Saving Rice Farming Affects Nitrifiers In Soil

Nitrification is a microbially mediated process wherein bacterial and archaeal nitrifiers oxidize ammonium (NH4+) to nitrite (NO2-) and then to nitrate (NO3-). The activity of nitrifiers largely determines the pool size of plant-available inorganic nitrogen (N) in soils. Nitrifier activity in the rhizosphere is affected by the nature of root exudates, competition with other soil organisms, oxygen availability and plant demand for NH4+-N in soil. Nitrification in flooded paddy rice soils has been studied extensively; however, our understanding of the dynamics of nitrifiers in water-saving rice farming systems is limited. I studied the effects of three water management regimes (continuously flooded - CF; alternating wetting and drying - AWD; and, aerobic cultivation - AC), on nitrifier populations inhabiting the rice rhizosphere. A series of greenhouse experiments was conducted to study plant response to water management and the effect of water management regime on soil nitrifiers at different plant growth stages using five rice varieties. The rhizosphere oxidizing power, the preferred N form (NH4+and/or NO3-) of each rice variety, and the effects of rootderived secondary metabolites on nitrifiers were also studied. The five rice varieties differed significantly in these response variables. The biomass of all five rice varieties was higher when N was supplied in a mixed form, than when N was supplied as either NH4+ or NO3- alone. The physiological N use efficiency (PNUE) of plants was significantly affected by rice variety and the ratio of NH4+ to NO3- in the growth medium. At 0.50 mg ml-1 concentration, root exudates enhanced the activity of Nitrosomonas europaea, an ammonia oxidizing bacterium, but a water extract from crushed rice roots inhibited its activity. Continuous exposure to plant roots for 14 days reduced the nitrifiers' potential activity in soil by 50%. Biomass production was lower and rooting depth and rhizosphere nitrification were higher under AC as compared to CF. Rice variety and water management practice interactively affected the activity and composition of nitrifier communities in the rice soils, which had follow-on effects on biomass production. Understanding these interactions is necessary to help practitioners manage N more effectively in relation to cultivars used and water management strategies adopted

Evaluating the nitrification inhibition potential of selected botanicals and their non-target effects

Nitrification inhibitors (NI) are aimed at improving N-fertilizer use efficiency in cropping systems. This study aimed to assess the nitrification inhibition potential and non-target effects of dry leaf powders (botanicals) of ten plant species [neem (Azadirachta indica), lantana (Lantana camara), karanda (Pongamia pinnata), Brachiaria humidicola, cinnamon (Cinnamomum verum), clove (Syzygium aromaticum), wild-sunflower (Tithonia diversifolia), mee (‎Madhuca longifolia), nutmeg (Myristica fragrans) and pepper (Piper nigram)]. The effect of botanicals on the growth of three ammonia oxidizing bacteria isolates (M4, M5 and M7) and NO3The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Woodchip biochar with or without synthetic fertilizers affects soil properties and available phosphorus in two alkaline, Chernozemic soils

Fertility enhancement with biochar application is well documented for tropical acidic soils; however, benefits of biochar co-applied with synthetic fertilizers on soil fertility are not well documented, particularly for alkaline chernozems. We examined the short-term interactive effects of woodchip biochar amendment with fertilizers on selected soil properties, available phosphorus (P) and P fractions of two alkaline Chernozems from Manitoba. Treatments were (1) urea and monoammonium phosphate fertilizers, (2) biochar at 10 g kgThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Antibiotic use in commercial broiler chicken farming and its consequential resistance development in root colonizing bacteria of carrot grown in manure applied soils in a middle-income country

Broiler chicken litter (BCL) is a cheap manure for vegetable crops in developing countries. Extensive antibiotic use in poultry production could increase antibiotic resistant bacteria (ARB) in manure and eventually in crop root-microbiome. We investigated the prevalence of ARB in BCL from medium- and large-scale farms (n=33) and in carrot (Dacus carotova) grown in BCL applied soils in Sri Lanka. All the BCL samples contained aerobic bacteria resistant to 10 g/mL of oxytetracycline or enrofloxacin. The abundance of ARB determined by viable plate-count method ranged from 0.05% to 30.10% of aerobic bacterial population. Soil from two fields applied with BLC for three years (short history, SH) and ten years (long history, LH) were treated with BCL (10%, w/w) and oxytetracycline (10 and 100 mg/kg) in a pot experiment alongside an un-amended control. Adding BCL and oxytetracycline had a significant (PThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author