Vis-NIR spectroscopy based rapid and non-destructive method to quantitate microplastics: An emerging contaminant in farm soil.

Microplastics (MPs) is the second most important environmental issue and can potentially enter into food chain through farmland contamination and other means. There are no standardized extraction methods for quantification of MPs in soil. The embedded errors and biases generated serious problems regarding the comparability of different studies and leading to erroneous estimation. To address this gap, present study was formulated to develop an efficient method for MPs analysis suitable for a wide range of soil and organic matrices. A method based on Vis-NIR (Visible-Near Infra Red) spectroscopy is developed for four different soil belonging to Alfisol, Inceptisol, Mollisol and Vertisol and two organic matter matrices (FYM and Sludge). The developed method was found as rapid, reproducible, non-destructive and accurate method for estimation of all three-density groups of MPs (Low, Medium and High) with a prediction accuracy ranging from 1.9 g MPs/kg soil (Vertisol) to 3.7 g MPs/kg soil (Alfisol). Two different regression models [Partial Least Square Regression (PLSR) and Principal Component Regression (PCR)] were assessed and PLSR was found to provide better information in terms of prediction accuracy and minimum quantification limit (MQL). However, PCR performed better for organic matter matrices than PLSR. The method avoids any complicated sample preparation steps except drying and sieving thus saving time and acquisition of reflectance spectrum for single sample is possible within 18 s. Owing to have the minimum quantification limit ranging from 1.9-3.7 g/kg soil, the vis-NIR based method is perfectly suitable for estimation of MPs in soil samples collected from plastic pollution hotspots like landfill sites, regular based sludge amended farm soils. Additionally, the method can be adapted by small scale compost industries for assessing MPs load in product like city compost which are applied at agricultural fields and will be helpful in quantifying possible MPs at the sources itself.

Nitrification and urease inhibitors mitigate global warming potential and ammonia volatilization from urea in rice-wheat system in India: A field to lab experiment.

The efficacy of alternative nitrogenous fertilizers for mitigating greenhouse gas and ammonia emissions from a rice-wheat cropping system in northern India was addressed in a laboratory incubation experiment using soil from a 10-year residue management field experiment (crop residue removal, CRR, vs. incorporation, CRI). Neem coated urea (NCU), standard urea (U), urea ammonium sulfate (UAS), and two alternative fertilizers, urea + urease inhibitor NBPT (UUI) and urea + urease inhibitor NBPT + nitrification inhibitor DMPSA (UUINI) were compared to non-fertilized controls for four weeks in incubation under anaerobic condition. Effects of fertilizers on global warming potential (GWP) and ammonia volatilization were dependent on residue treatment. Relative to standard urea, NCU reduced GWP by 11 % in CRI but not significantly in CRR; conversely, UAS reduced GWP by 12 % in CRR but not significantly in CRI. UUI and UUINI reduced GWP in both residue treatments and were more effective in CRI (21 % and 26 %) than CRR (15 % and 14 %). Relative to standard urea, NCU increased ammonia volatilization by 8 % in CRI but not significantly in CRR. Ammonia volatilization was reduced most strongly by UUI (40 % in CRI and 37 % in CRR); it was reduced 28-29 % by UUINI and 12-15 % by UAS. Overall, the urease inhibitor, alone and in combination with the nitrification inhibitor, was more effective in mitigating greenhouse gas and ammonia emissions than NCU. However, these products need to be tested in field settings to validate findings from the controlled laboratory experiment.

Mitigation of yield-scaled greenhouse gas emissions from irrigated rice through Azolla, Blue-green algae, and plant growth-promoting bacteria.

Irrigated transplanted flooded rice is a major source of methane (CH4) emission. We carried out experiments for 2 years in irrigated flooded rice to study if interventions like methane-utilizing bacteria, Blue-green algae (BGA), and Azolla could mitigate the emission of CH4 and nitrous oxide (N2O) and lower the yield-scaled global warming potential (GWP). The experiment included nine treatments: T1 (120 kg N ha-1 urea), T2 (90 kg N ha-1 urea + 30 kg N ha-1 fresh Azolla), T3 (90 kg N ha-1 urea + 30 kg N ha-1 Blue-green algae (BGA), T4 (60 kg N ha-1 urea + 30 kg N ha-1 BGA + 30 kg N ha-1 Azolla, T5 (120 kg N ha-1 urea + Hyphomicrobium facile MaAL69), T6 (120 kg N ha-1 by urea + Burkholderia vietnamiensis AAAr40), T7 (120 kg N ha-1 by urea + Methylobacteruim oryzae MNL7), T8 (120 kg N ha-1 urea + combination of Burkholderia AAAr40, Hyphomicrobium facile MaAL69, Methylobacteruim oryzae MNL7), and T9 (no N fertilizer). Maximum decrease in cumulative CH4 emission was observed with the application of Methylobacteruim oryzae MNL7 in T7 (19.9%), followed by Azolla + BGA in T4 (13.2%) as compared to T1 control. N2O emissions were not significantly affected by the application of CH4-oxidizing bacteria. However, significantly lower (P<0.01) cumulative N2O emissions was observed in T4 (40.7%) among the fertilized treatments. Highest yields were observed in Azolla treatment T2 with 25% less urea N application. The reduction in yield-scaled GWP was at par in T4 (Azolla and BGA) and T7 (Methylobacteruim oryzae MNL7) treatments and reduced by 27.4% and 15.2% in T4 and T7, respectively, as compared to the T1 (control). K-means clustering analysis showed that the application of Methylobacteruim oryzae MNL7, Azolla, and Azolla + BGA can be an effective mitigation option to reduce the global warming potential while increasing the yield.

Methane production, oxidation and mitigation: A mechanistic understanding and comprehensive evaluation of influencing factors.

Methane is one of the critical greenhouse gases, which absorb long wavelength radiation, affects the chemistry of atmosphere and contributes to global climate change. Rice ecosystem is one of the major anthropogenic sources of methane. The anaerobic waterlogged soil in rice field provides an ideal environment to methanogens for methanogenesis. However, the rate of methanogenesis differs according to rice cultivation regions due to a number of biological, environmental and physical factors like carbon sources, pH, Eh, temperature etc. The interplay between the different conditions and factors may also convert the rice fields into sink from source temporarily. Mechanistic understanding and comprehensive evaluation of these variations and responsible factors are urgently required for designing new mitigation options and evaluation of reported option in different climatic conditions. The objective of this review paper is to develop conclusive understanding on the methane production, oxidation, and emission and methane measurement techniques from rice field along with its mitigation/abatement mechanism to explore the possible reduction techniques from rice ecosystem.

Biosorption of Cd(II) on jatropha fruit coat and seed coat.

Jatropha (Jatropha curcas L.) seed coat (JSC) and fruit coat (JFC) were investigated for adsorption of Cd(II) from aqueous solutions. JFC and JSC fine powders were characterized using FTIR and SEM which indicated that both the adsorbents have high surface area, pore space on their surface, and anionic sites for metal ion binding. Batch adsorption study was conducted to study the effect of adsorption time, agitation speed, and initial concentration of Cd(II) ion, pH, and temperature on the adsorption of Cd(II) by adsorbents. The equilibrium isotherm, kinetics, and thermodynamics of the adsorption process were studied. Adsorption equilibrium followed both Langmuir and Freundlich isotherm. The adsorption capacity (Q m ) of Cd(II) on JSC and JFC were 22.83 and 21.97 mg g(-1), respectively. The adsorption of Cd(II) on JSC and JFC is endothermic in nature. The change of free energy (∆G) of the biosorption of Cd(II) on JSC ranged from -37.05 to -40.54 kJ mol(-1) and for JFC -34.50 to -37.35 kJ mol(-1). The enthalpy change (∆H) and entropy change (∆S) was 15.84 kJ mol(-1) and -0.17 kJ mol(-1) K(-1) for JSC and 8.77 kJ mol(-1) and -0.14 kJ mol(-1) K(-1) for JFC. Elovich model provided a better correlation of the experimental data in comparison with pseudo-first-order and pseudo-second-order kinetic models. The study indicated that JFC and JSC have good adsorption capacity for Cd(II).

Greenhouse gas mitigation in rice-wheat system with leaf color chart-based urea application.

Conventional blanket application of nitrogen (N) fertilizer results in more loss of N from soil system and emission of nitrous oxide, a greenhouse gas (GHG). The leaf color chart (LCC) can be used for real-time N management and synchronizing N application with crop demand to reduce GHG emission. A 1-year study was carried out to evaluate the impact of conventional and LCC-based urea application on emission of nitrous oxide, methane, and carbon dioxide in a rice-wheat system of the Indo-Gangetic Plains of India. Treatments consisted of LCC scores of ≤4 and 5 for rice and wheat and were compared with conventional fixed-time N splitting schedule. The LCC-based urea application reduced nitrous oxide emission in rice and wheat. Application of 120 kg N per hectare at LCC ≤ 4 decreased nitrous oxide emission by 16% and methane by 11% over the conventional split application of urea in rice. However, application of N at LCC ≤ 5 increased nitrous oxide emission by 11% over the LCC ≤ 4 treatment in rice. Wheat reduction of nitrous oxide at LCC ≤ 4 was 18% as compared to the conventional method. Application of LCC-based N did not affect carbon dioxide emission from soil in rice and wheat. The global warming potential (GWP) were 12,395 and 13,692 kg CO(2) ha(-1) in LCC ≤ 4 and conventional urea application, respectively. Total carbon fixed in conventional urea application in rice-wheat system was 4.89 Mg C ha(-1) and it increased to 5.54 Mg C ha(-1) in LCC-based urea application (LCC ≤ 4). The study showed that LCC-based urea application can reduce GWP of a rice-wheat system by 10.5%.

Simulation of nitrogen dynamics in soil using infocrop model.

Nitrogen is the most widely used fertilizer nutrient, and it is a universally deficient nutrient too, which often severely restricts the growth and yield of crops. To improve N fertilizer management, soil-plant system models can be applied to simulate adequate N supply for both, optimal crop growth and minimal N losses. The likely impact of climate change on the cereal production is of paramount importance in the planning strategies to meet the future growing needs on sustainable grounds. In this scenario models are the effective tools to foresee the probable impacts and for choosing appropriate land use options. The study reported in this thesis, employs field experiments and use of simulation tools to understand the dynamics of soil N balance and relate growth and yield of rice under varying nitrogen inputs. The InfoCrop model was used in this study, which was calibrated with the historic data sets, and subsequently validated with the field experiment conducted at IARI Farm, New Delhi. Simulated results matched well with the observed values in terms of growth and yield of rice and seasonal nitrogen uptake. The components of soil nitrogen balance differed among varying nitrogen level treatments, which was also captured by use of InfoCrop. The model was then taken to climate change impact analysis. The results clearly revealed that when temperature increased, the soil N losses, like denitrification, volatilization, N2O emission increased, whereas grain and biomass yields decreased. The further scope of the study is to validate the study in contrasting agroenvironments.

Mitigating nitrous oxide and methane emissions from soil in rice-wheat system of the Indo-Gangetic plain with nitrification and urease inhibitors.

Mitigation of methane (CH4) and nitrous oxide (N2O) emissions from soil is important to reduce the global warming. Efficacy of five nitrification inhibitors, i.e. neem (Azadirachta melia) cake, thiosulphate, coated calcium carbide, neem oil coated urea and dicyandiamide (DCD) and one urease inhibitor, hydroquinone, in mitigating N2O and CH4 emissions from fertilized soil was tested in rice-wheat system in the Indo-Gangetic plains. The closed chamber technique was used for the collection of gas samples, which were analyzed using gas chromatography. Reduction in N2O emission on the application of nitrification/urease inhibitors along with urea ranged from 5% with hydroquinone to 31% with thiosulphate in rice and 7% with hydroquinone to 29% with DCD in wheat crop. The inhibitors also influenced the emission of CH4. While application of neem coated urea, coated calcium carbide, neem oil and DCD reduced the emission of CH4; hydroquinone and thiosulphate increased the emission when compared to urea alone. However, the global warming potential was lower with the inhibitors (except hydroquinone) as compared to urea alone, suggesting that these substances could be used for mitigating greenhouse gas emission from the rice-wheat systems.