Effect of N and water management on greenhouse gas emission and N availability in paddy soils of Bangladesh

Soil moisture and nitrogen (N) are the two important factors determining growth and yield of rice along with their vital influence on paddy soil emission of CH4, N2O and CO2, N mineralization and possibly micronutrient availability. Rice cultivation by alternate wetting and drying (AWD), instead of conventional/continuous flooding (CF), is expanding in South-East Asia due to shortage of irrigation water. However, studies comparing the influence of irrigation management on GHG emission, soil N availability, biochemical soil parameters and available content of micronutrients is still lacking for young floodplain soils in Bangladesh. We assessed the consequence of AWD and direct seeded (DS) rice on CH4, N2O and CO2 emissions, N mineralization, and micronutrients availability compare to CF in a paddy field experiment at the Bangladesh Agricultural University in the 2014 Boro season. The cultivated rice variety (BRRI dhan28) was grown for 14 weeks with (T2: N120) or without N fertilizer (T1:N0) (subplot) supply under three water management practices (CF, AWD and DS). Global warming potentials (GWPs) based on cumulative emissions of CH4, CO2 and N2O were compared. In addition dissolved organic carbon (DOC), Fe, Mn and Zn content in soil solution, collected at two depths (0-6cm and 6-12cm) were measured biweekly. Grain and straw yield parameters were recorded during harvest. Water management practices had no large influences on the evolution of mineral N (NH4-N+NO3-N) (mg kg-1) over time. On the opposite, CH4 fluxes (mg m-2 h-1) over time varied widely between the water management practices. As expected, CH4 fluxes in all the continuously flooded (CF) soils were higher compared to AWD and DS plots. Also differences between CH4 emissions of the N0 and N120 treatments were high with CF, low with AWD and negligible with DS management. The N applied CF and AWD plots had higher CH4 fluxes compared to those of the nil N application objects (N0). Analyses of released CO2 and N2O and fixed NH4 are still on-going. The DOC content in pore water increased gradually during 12 weeks of rice growing regardless water management, N fertilization and soil depth. At any time the DOC content was higher under CF and AWD compare to DS management. The Fe content in soil pore solution was higher and the Mn content was lower in CF compare to AWD, suggesting more Fe reduction in the former case. The content of Zn was unaffected by irrigation and N management. The average grain yield (t ha-1) in N fertilized AWD plots was 9 and 17% higher than those of CF and DS plots, respectively. Based on all these results we conclude that rice growing through AWD decreased CH4 emissions without any influence on grain yield, despite limiting the availability of Fe in subtropical paddy soils

Forest fire flame and smoke detection from UAV-captured images using fire-specific color features and multi-color space local binary pattern

In recent years, the frequency and severity of forest fire occurrence have increased, compelling the research communities to actively search for early forest fire detection and suppression methods. Remote sensing using computer vision techniques can provide early detection from a large field of view along with providing additional information such as location and severity of the fire. Over the last few years, the feasibility of forest fire detection by combining computer vision and aerial platforms such as manned and unmanned aerial vehicles, especially low cost and small-size unmanned aerial vehicles, have been experimented with and have shown promise by providing detection, geolocation, and fire characteristic information. This paper adds to the existing research by proposing a novel method of detecting forest fire using color and multi-color space local binary pattern of both flame and smoke signatures and a single artificial neural network. The training and evaluation images in this paper have been mostly obtained from aerial platforms with challenging circumstances such as minuscule flame pixels, varying illumination and range, complex backgrounds, occluded flame and smoke regions, and smoke blending into the background. The proposed method has achieved F1 scores of 0.84 for flame and 0.90 for smoke while maintaining a processing speed of 19 frames per second. It has outperformed support vector machine, random forest, Bayesian classifiers and YOLOv3, and has demonstrated the capability of detecting challenging flame and smoke regions of a wide range of sizes, colors, textures, and opacity.The 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

Control of paddy soil redox condition on gross and net ammonium fixation and defixation

Abiotic fixation and defixation of ammonium (NH4+) in silicate interlayers are common processes in paddy soils, owing to their often high levels of 2:1 type clay minerals. Fixed NH4+ hence forms a buffer during the supply and loss of plant-available N. The soil redox potential (E-h) is suspected to influence NH4+ (de)fixation by its impact on the negative charge of Fe3+-containing clay minerals, yet experimental confirmations are scarce. We examined the effect of a fluctuating or generally increased E-h on dynamics of NH4+ (de)fixation in a Bangladeshi paddy soil (total N: 1.9 g kg(-1) vertical bar CEC: 43 cmol kg(-1)) during two incubation experiments. In those, we either N-15-labelled the fixed NH4+ pool (with initially 87 mg kg(-1) exchangeable versus 393 mg kg(-1) fixed NH4+-N) or the exchangeable pool (with initially 141 mg kg(-1) exchangeable versus 249 mg kg(-1) fixed NH4+-N), and this under three E-h-controlling treatments: continuous flooding (CF), CF with extra MnO2 added (3.5 g kg(-1) Mn-4(+)) (CF-MnO2), and alternate wetting and drying (AWD). The CF treatment overall led to somewhat higher net NH4+ fixation than AWD and, less clearly, also compared to the CF-MnO2 treatment, resulting from higher gross NH4+ fixation as well as lower gross defixation. These fluxes always led to a dynamic equilibrium between the exchangeable and fixed NH4+ pool within a few days of incubation, and this equilibrium was the same for both experiments but depended on the E-h treatment. However, by altering other NH4+ transformation processes, E-h treatments also indirectly impacted NH4+ (de)fixation fluxes, for which the equilibrium ratio between exchangeable versus fixed NH4+ turns out to be the determining factor

Stable isotopes to understand paddy soil biogeochemical processes under water-saving irrigation

To cope with climate change, the use of water-saving irrigation practices in rice production is increasingly promoted, instead of the traditional practice of continuous flooding. Yet, it is unclear how the periodic introduction of oxygen during drying events impacts some fundamental biogeochemical processes in paddy soils because of the difficulty to quantify them. This knowledge gap actually complicates the development of mechanistic biogeochemical models, which are key for the prediction of paddy soil nutrient dynamics over a range of edaphic, agronomic and climatic settings. However, stable isotopes may help to shed some light on dynamics of important soil nutrients, i.e., by exploiting their natural or artificial (by labelling) variations over different biogeochemical transformations. In an effort to improve their implementation in soil models, we experimentally investigated the effect of water-saving irrigation management on three prominent but understudied carbon and nitrogen transformations in paddy soils from Italy and Bangladesh by means of stable isotopes. In particular, we assessed the oxidation of methane (CH4) in situ, the decomposition of soil organic carbon (SOC) after the incorporation of organic residues, and the fixation and defixation of ammonium (NH4+) in clay interlayers, always as a function of irrigation management. As it turns out, the adoption of water-saving irrigation practices had the potential to relatively stimulate in situ CH4 oxidation, in spite of some methodological difficulties, which implies that the commonly observed lower CH4 emissions in paddy fields under water-saving irrigation probably do not only stem from lower CH4 production rates under less anaerobic conditions, but also from this mitigation mechanism. Secondly, the stimulation of native SOC dissolution after the incorporation of organic residues was restricted under water-saving irrigation, and redox-active iron oxides with sorbed SOC potentially play a role in this. However, this effect on SOC dissolution was not proportionally reflected in SOC-derived emissions of CH4 and carbon dioxide (CO2), so that irrigation management probably does not influence these emissions and the long-term SOC balance through the proposed mechanism. Thirdly, the effect of irrigation management on abiotic fixation and defixation dynamics of NH4+ into or from interlayers of clay minerals was rather limited, but these processes – which determine the bioavailability of NH4+ in paddy soil – were instead predominantly dictated by an equilibrium between bioavailable and clay-fixed NH4+ phases. Overall, with a well-considered experimental setup in which untargeted isotope contrasts can be quantified and the appropriate pools sampled, stable isotopes are apparently a powerful tool to quantify gross nutrient transformations in paddy soil

Is there a link between reduction of Fe and Mn and anaerobic N mineralization in floodplain paddy soils in Bangladesh?

The N mineralization in wetland paddy soils is influenced by a multitude of physicochemical factors. Previous experimental work revealed no relationship at all between anaerobic soil N mineralization and mineralogy or soil organic matter composition in Bangladeshi young floodplain paddy soils. We therefore hypothesized that the anaerobic biological activity in these soils instead depends on availability of alternative electron acceptors. We hypothesized reducible Fe3+ and Mn4+ content to determine anaerobic SOM mineralization and thereby NH4+ release in soils from Northern Bangladesh. We compared NH4 and soil solution parameters in incubated soil collected from field experimental plots and farmers’ fields. We assessed the influence of Fe and Mn application on anaerobic N mineralization in lab incubation experiments. Finally, we investigated the contribution of abiotic release of fixed NH4+ on mineral N production relative to biotic anaerobic N mineralization. Soils were collected, firstly from five fertilizer application treatments (Control, N, NP, NPK and N+FYM) from a long-term field experiment with double rice cropping at the Bangladesh Agricultural University (BAU) and secondly from four farmers’ paddy fields. All soils were either treated with Fe2O3 (T2), Mn/Al mixed oxides (T3) or were left untreated (T1) and were anaerobically incubated. pH, Fe, Mn and dissolved OC in soil solution were followed by use of rhizon moisture samplers and produced CH4 and CO2 were measured at a regular interval. The KCl-extractable NH4+, microbial biomass carbon (MBC) and pH-KCl at the end of the experiment were also determined. Generally, over all five fertilizer treatments there were no considerable differences in soil solution Fe and Mn concentrations between T1 and T2 treatments. The KCl extractable NH4+ content increased by 12 to 37 mg kg-1 after 8 weeks, but the differences among the Fe or Mn treated and untreated soils were insignificant. For the four studied farmers’ fields The NH4+ release patterns were asymptotic with no differences among the treatments (T1, T2 and T3). The total NH4+ released ranged from 25 to 54 mg kg-1 during 10 weeks of anaerobic incubation. The results indicated that the availability of Mn4+ and Fe3+ did not have any effect on anaerobic N mineralization. Rather, application of amorphous Mn-oxides merely retarded Fe dissolution and CH4 production. Finally, non-exchangeable (i.e. fixed) NH4+-N and MBC of anaerobically incubated untreated farmers’ fields soils were measured. The amount of non-exchangeable NH4+-N differed significantly among the four soils and increased significantly after 2 and 4 weeks of flooding. In all soils, the MBC already reached a maximum after 2 weeks of flooding (0.6 to 2.3% of total SOC), in close correspondence to the fast rise in exchangeable NH4+ after flooding. We conclude that the exchangeable NH4 in these farmers’ fields paddy soils is mainly derived from anaerobic N mineralization and not from the release of fixed-NH4+

In vitro Evaluation of Antioxidant Potential of Leaves of

Antioxidant potential of the 80 % methanol extract of the leaves of Opuntia dillenii was evaluated using 1, 1-diphenyl, 2-picryl hydrazyl (DPPH) and nitric oxide radical scavenging, reducing power, total phenol and total flavonoid content determination assays. Preliminary phytochemical screening of the extract was also carried out, which revealed that the extract possesses flavonoids, steroids, alkaloids and tannins. The extract showed significant antioxidant activities in all antioxidant assays compared to the reference antioxidant in a dose dependent manner. In DPPH radical scavenging activity, the IC50 value of the crude extract was found to be 15.71μg/mL while the IC50 value for the reference ascorbic acid was 10.84 μg/mL. Again, the extract showed remarkable nitric oxide scavenging potential and good reducing power. Moreover, the methanol extract was found to contain high amount of phenols and flavonoids, expressed as gallic acid and rutin equivalents respectively. Based on the findings of the present study, we conclude that the methanol extract of the leaves of O. dillenii possesses remarkable antioxidant potential which may be attributed to the high amount of phenols and flavonoids present in the extract