Nitrous oxide and nitric oxide fluxes differ from tea plantation and tropical forest soils after nitrogen addition

South Asia is experiencing a rapid increase in nitrogen (N) pollution which is predicted to continue in the future. One of the possible implications is an increase in gaseous reactive N losses from soil, notably in the form of nitrous oxide (N2O) and nitric oxide (NO). Current knowledge of N2O and NO dynamics in forest ecosystems is not sufficient to understand and mitigate the impacts on climate and air quality. In order to improve the understanding of emissions from two major land uses in Sri Lanka, we investigated the emission potential for N2O and NO fluxes measured by absorption spectroscopy and chemiluminescence, respectively, in response to three different N addition levels (the equivalent of 0, 40 and 100 kg N ha−1 yr.−1 deposition in the form of NH4+) from soils of two typical land uses in Sri Lanka: a secondary montane tropical forest and a tea plantation using soil laboratory incubations of repacked soil cores. We observed an increase in NO fluxes which was directly proportional to the amount of N applied in line with initial expectations (maximum flux ranging from 6–8 ng NO-N g−1 d−1 and from 16–68 ng NO-N g−1 d−1 in forest and tea plantation soils, respectively). However, fluxes of N2O did not show a clear response to N addition, the highest treatment (100 N) did not result in the highest fluxes. Moreover, fluxes of N2O were higher following the addition of a source of carbon (in the form of glucose) across treatment levels and both land uses (maximum flux of 2–34 ng N2O-N g−1 d−1 in forest and 808–3,939 ng N2O-N g−1 d−1 in tea plantation soils). Both N2O and NO fluxes were higher from tea plantation soils compared to forest soils irrespective of treatment level, thus highlighting the importance of land use and land management for gaseous reactive N fluxes and therefore N dynamics

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

Estimation of ammonia deposition to forest ecosystems in Scotland and Sri Lanka using wind-controlled NH3 enhancement experiments

Ammonia (NH3) pollution has emerged as a major cause of concern as atmospheric concentrations continue to increase globally. Environmentally damaging NH3 levels are expected to severely affect sensitive and economically important organisms, but evidence is lacking in many parts of the world. We describe the design and operation of a wind-controlled NH3 enhancement system to assess effects on forests in two contrasting climates. We established structurally identical NH3 enhancement systems in a temperate birch woodland in the UK and a tropical sub-montane forest in central Sri Lanka, both simulating real-world NH3 pollution conditions. Vertical and horizontal NH3 concentrations were monitored at two different time scales to understand NH3 transport within the forest canopies. We applied a bi-directional resistance model with four canopy layers to calculate net deposition fluxes. At both sites, NH3 concentrations and deposition were found to decrease exponentially with distance away from the source, consistent with expectations. Conversely, we found differences in vertical mixing of NH3 between the two experiments, with more vertically uniform NH3 concentrations in the dense and multi-layered sub-montane forest canopy in Sri Lanka. Monthly NH3 concentrations downwind of the source ranged from 3 to 29 μg m−3 at the UK site and 2–47 μg m−3 at the Sri Lankan site, compared with background values of 0.63 and 0.35 μg m−3, respectively. The total calculated NH3 dry deposition flux to all the canopy layers along the NH3 transects ranged from 12 to 162 kg N ha−1 yr−1 in the UK and 16–426 kg N ha−1 yr−1 in Sri Lanka, representative of conditions in the vicinity of a range of common NH3 sources. This multi-layer model is applicable for identifying the fate of NH3 in forest ecosystems where the gas enters the canopy laterally through the trunk space and exposes the understorey to high NH3 levels. In both study sites, we found that cuticular deposition was the dominant flux in the vegetation layers, with a smaller contribution from stomatal uptake. The new facilities are now allowing the first ever field comparison of NH3 impacts on forest ecosystems, with special focus on lichen bio-indicators, which will provide vital evidence to inform NH3 critical levels and associated nitrogen policy development in South Asia

Climate Change Impacts on Rice Farming Systems in Northwestern Sri Lanka

Sri Lanka has achieved tremendous progress since 1950 in crop production and food availability. Yields grew at an impressive rate until leveling off in the mid-eighties. Sri Lanka's population is anticipated to grow in the coming decades, creating an ever-greater demand for food security on the household, sub-district, regional, and national scales.The agricultural sector in Sri Lanka is vulnerable to climate shocks. An unusual succession of droughts and floods from 2008 to 2014 has led to both booms and busts in agricultural production, which were reflected in food prices. In both instances, the majority of farmers and consumers were adversely affected.At present the rice-farming systems are under stress due to inadequate returns for the farmers and difficulty in coping with shocks due to climate, pests, and diseases, and prices for produce. There are government price-support mechanisms, fertilizer-subsidy schemes, and crop insurance schemes, but the levels of the supports are modest and often do not effectively reach the farmers

Comparison of nutritional and trace element concentrations in some Sri Lankan traditional rice varieties

Recently, traditional rice cultivars have become more popular than new, enhanced rice varieties, with the main focus being on their health benefits. Few rice cultivars have been thoroughly studied to understand their nutritional and health benefits. Inductively coupled plasma atomic emission/mass spectroscopy methods were used to determine the concentrations of 24 key nutrients and trace elements in 104 traditional rice types (Oryza sativa L.) grown in Sri Lanka. Compared to the Codex Alimentarius provisional tolerable daily intake for 24 different elements, the concentrations of toxic elements such as As, Cd, Pb and Cr were significantly lower (P < 0.05), and most of the nutritional elemental concentrations were substantially higher (P < 0.05) in evaluated traditional rice varieties. Furthermore, Pb, Bi, B, K, Mg, S, Zn and Fe concentrations among traditional rice varieties were not substantially different (P > 0.05). Notably, several traditional rice varieties (i.e. Rathu Heenati, Pragathi Wee, Weda Heenati, etc.) contained significantly high levels of selenium (& AP;250 & mu;g L-1 DM, P < 0.05), an important trace element that is deficient in the diets of 1 billion people globally

Calibration of the phenology sub-model of APSIM-Oryza: Going beyond goodness of fit

International audienceParameterizing the phenology of new crop varieties is a major challenge in crop modeling. Here we consider calibration of the phenology sub-model of the widely used crop model APSIM-Oryza, using commonly available varietal data. We show that the dynamic phenology sub-model can be well approximated by a static model, with three equations. It is then straightforward to estimate the parameters using any standard statistical software package. The approach is applied to four rice varieties from Sri Lanka. The software provides not only the best-fit parameters, but also uncertainty information about those parameters. This is essential for understanding how well the model will predict out of sample. Here the photoperiod sensitivity coefficient has large uncertainty, and so predictions for day lengths outside the data set are very unreliable. The uncertainty information is also used to show that in our case, doing more field trials would have very little effect on uncertainty

Accounting for both parameter and model structure uncertainty in crop model predictions of phenology: A case study on rice

We consider predictions of the impact of climate warming on rice development times in Sri Lanka. Themajor emphasis is on the uncertainty of the predictions, and in particular on the estimation of meansquared error of prediction. Three contributions to mean squared error are considered. The first is param-eter uncertainty that results from model calibration. To take proper account of the complex data structure,generalized least squares is used to estimate the parameters and the variance-covariance matrix of theparameter estimators. The second contribution is model structure uncertainty, which we estimate usingtwo different models. An ANOVA analysis is used to separate the contributions of parameter and modeluncertainty to mean squared error. The third contribution is model error, which is estimated usinghindcasts. Mean squared error of prediction of time from emergence to maturity, for baseline +2◦C,is estimated as 108 days2, with model error contributing 86 days2, followed by model structure uncer-tainty which contributes 15 days2and parameter uncertainty which contributes 7 days2. We also showhow prediction uncertainty is reduced if prediction concerns development time averaged over years, orthe difference in development time between baseline and warmer temperatures

Meteorological data and ammonia concentration and deposition rates from an ammonia enhancement experiment site, Queensberry, Sri Lanka, 2022

This dataset contains information about meteorological conditions and ammonia concentration and deposition rates resulting from an experimental setup. An NH3 enhancement experiment along with a full suite of multi-height meteorological measurements was established in a tropical forest in central Sri Lanka. Under suitable wind conditions measured at the meteorological tower, NH3 is released towards two monitoring transects. Along the downwind monitoring transects, NH3 concentrations in the air are measured using monthly passive samplers. Deposition rates are modelled using a bi-directional resistance model based on measured NH3 concentrations in the air, micrometeorology and plant physiology. Additionally, NH3 concentrations were measured at high temporal resolution at a fixed downwind distance from the source to achieve the target enhancement concentrations. The work was supported by UKRI GCRF South Asian Nitrogen Hub (Grant NE/S009019/1)