• Energy Research

Abstract Soil methane (CH4) and nitrous oxide (N2O) fluxes are difficult to predict from soil temperature and moisture alone, especially compared to carbon dioxide (CO2) fluxes. That difficulty is reflected in high spatial and temporal (spatiotemporal) variability of these two greenhouse gases (GHGs). We used a 16 ha field, under homogeneous soils and vegetation, to simultaneously explore spatial and temporal variability of soil CH4 and N2O fluxes. We also measured soil physical and chemical properties in order to explain, and predict, spatial variability of these two gases. Gas fluxes were measured using either a dynamic chamber (spatial variability study) or automated chambers using FTIR (temporal variability study). Soil samples were analysed for 30 chemical parameters (including at least two forms of soil carbon and nitrogen), while two proximal soil sensors were used to collect fine-resolution soil electrical conductivity and gamma radiometric concentration across the site. Fluxes of CH4 and N2O showed distinct spatial patterns, and were uniquely related to soil properties. Spatial variability in both CH4 and N2O fluxes was greater than five months of temporal variability (an increase in 112% and 39% in standard deviations for each gas respectively). If we relied solely on the autochambers for mean field fluxes, we would have underestimated fluxes by 59 and 197%, for CH4 and N2O respectively. CH4 fluxes were more spatially-dependent than those of N2O (semivariance analysis), but both showed greater spatial dependence than previously reported. Nearly 40 and 50% of the mean spatial flux of CH4 and N2O were from 1% of the area. Spatial variability in soil CH4 fluxes was predicted best by electrical conductivity measurements at 0–50 cm (r = 0.74) and soil C. Soil N2O fluxes, on the other hand, were predicted best by soil N and the gamma radiometric data (r = 0.48). Overall, our results clearly show that the large spatial variance of both CH4 and N2O fluxes requires great caution when scaling from chamber-based measurements to the field and beyond. Proximal sensors (as used here) can help map “hot spots” of soil CH4 and N2O fluxes at the field scale.

International audience

Air temperature is an important microclimate parameter in a greenhouse as it influences root growth and controls plant growth and development. Thus, the precise monitor and model temperature under greenhouse is needed to maintain the plants in optimal conditions. This research aims to model the temperature under a greenhouse using energy balance model. The study monitored the temperature inside and outside the greenhouse in a humid tropical environment. Based on the data, heat exchange constants of greenhouse components were derived, they were: 0.0029 (solar radiation), 0.8 (air) and 0.01 (heat exchange from greenhouse component). The calibrated model enables the calculation of temperature inside a greenhouse based on its outside air temperature, wind speed, and solar radiation. Testing the model against an independent time series showed the high accuracy of the model with an R2 value of 0.99, RMSE = 0.0085 and model efficiency Ef = 0.99. Based on the results, most advantageous strategies for air temperature control inside the greenhouse include the control of air ventilation.

Volcanic eruptions affect land and humans globally. When a volcano erupts, tons of volcanic ash materials are ejected to the atmosphere and deposited on land. The hazard posed by volcanic ash is not limited to the area in proximity to the volcano, but can also affect a vast area. Ashes ejected from volcano’s affect people’s daily life and disrupts agricultural activities and damages crops. However, the positive outcome of this natural event is that it secures fertile soil for the future. This paper examines volcanic ash (tephra) from a soil security view-point, mainly its capability. This paper reviews the positive aspects of volcanic ash, which has a high capability to supply nutrients to plant, and can also sequester a large amount of carbon out of the atmosphere. We report some studies around the world, which evaluated soil organic carbon (SOC) accumulation since volcanic eruptions. The mechanisms of SOC protection in volcanic ash soil include organo-metallic complexes, chemical protection, and physical protection. Two case studies of volcanic ash from Mt. Talang and Sinabung in Sumatra, Indonesia showed the rapid accumulation of SOC through lichens and vascular plants. Volcanic ash plays an important role in the global carbon cycle and ensures soil security in volcanic regions of the world in terms of boosting its capability. However, there is also a human dimension, which does not go well with volcanic ash. Volcanic ash can severely destroy agricultural areas and farmers’ livelihoods. Connectivity and codification needs to ensure farming in the area to take into account of risk and build appropriate adaptation and resilient strategy.

AbstractTropical peatlands are vital ecosystems that play an important role in global carbon storage and cycles. Current estimates of greenhouse gases from these peatlands are uncertain as emissions vary with environmental conditions. This study provides the first comprehensive analysis of managed and natural tropical peatland GHG fluxes: heterotrophic (i.e. soil respiration without roots), total CO2 respiration rates, CH4 and N2O fluxes. The study documents studies that measure GHG fluxes from the soil (n = 372) from various land uses, groundwater levels and environmental conditions. We found that total soil respiration was larger in managed peat ecosystems (median = 52.3 Mg CO2 ha−1 year−1) than in natural forest (median = 35.9 Mg CO2 ha−1 year−1). Groundwater level had a stronger effect on soil CO2 emission than land use. Every 100 mm drop of groundwater level caused an increase of 5.1 and 3.7 Mg CO2 ha−1 year−1 for plantation and cropping land use, respectively. Where groundwater is deep (≥0.5 m), heterotrophic respiration constituted 84% of the total emissions. N2O emissions were significantly larger at deeper groundwater levels, where every drop in 100 mm of groundwater level resulted in an exponential emission increase (exp(0.7) kg N ha−1 year−1). Deeper groundwater levels induced high N2O emissions, which constitute about 15% of total GHG emissions. CH4 emissions were large where groundwater is shallow; however, they were substantially smaller than other GHG emissions. When compared to temperate and boreal peatland soils, tropical peatlands had, on average, double the CO2 emissions. Surprisingly, the CO2 emission rates in tropical peatlands were in the same magnitude as tropical mineral soils. This comprehensive analysis provides a great understanding of the GHG dynamics within tropical peat soils that can be used as a guide for policymakers to create suitable programmes to manage the sustainability of peatlands effectively.

A nature-based soil security solution is proposed. In countries with active volcanoes, such as Indonesia, volcanic ash could be used to supply nutrients and reduce CO2 from the atmosphere. The weathering can draw CO2 from the atmosphere; in addition, volcanic ash with 0% carbon can turn into soils with around 10% organic carbon. In Indonesia, soils of volcanic origin cover about 31.7 million ha or 17% of its land area. Frequent volcanic eruptions made volcanic ash or tephra readily available. However, tephra is not widely used and has not been adequately investigated as a soil amendment to sequester carbon. This paper calculates the magnitude and opportunity of CO2 drawdown potential from volcanic materials produced annually in Indonesia. In years with significant volcanic eruptions, the subsequent withdrawal will be 100–200 Mt CO2 or 20–40% of the country's fossil fuel emission. The CO2 captured when volcanic materials weather is part of the global carbon cycle and is influenced by land-use decisions. Currently, volcanic ash is often eroded and rapidly transferred to aquatic systems. In relevant landscapes, actively managing this untapped resource is more feasible than external basalt applications as volcanic ashes do not need to be ground, can soak up significant amounts of carbon from the atmosphere, and build fertile soils that supply an abundance of nutrients to achieve food and soil security. Volcanic ash needs to be included in carbon accounting and its management could be part of emission reduction strategies.

The ‘4 per mille Soils for Food Security and Climate’ was launched at the COP21 with an aspiration to increase global soil organic matter stocks by 4 per 1000 (or 0.4 %) per year as a compensation for the global emissions of greenhouse gases by anthropogenic sources. This paper surveyed the soil organic carbon (SOC) stock estimates and sequestration potentials from 20 regions in the world (New Zealand, Chile, South Africa, Australia, Tanzania, Indonesia, Kenya, Nigeria, India, China Taiwan, South Korea, China Mainland, United States of America, France, Canada, Belgium, England & Wales, Ireland, Scotland, and Russia). We asked whether the 4 per mille initiative is feasible for the region. The outcomes highlight region specific efforts and scopes for soil carbon sequestration. Reported soil C sequestration rates globally show that under best management practices, 4 per mille or even higher sequestration rates can be accomplished. High C sequestration rates (up to 10 per mille) can be achieved for soils with low initial SOC stock (topsoil less than 30 t C ha− 1), and at the first twenty years after implementation of best management practices. In addition, areas which have reached equilibrium will not be able to further increase their sequestration. We found that most studies on SOC sequestration only consider topsoil (up to 0.3 m depth), as it is considered to be most affected by management techniques. The 4 per mille number was based on a blanket calculation of the whole global soil profile C stock, however the potential to increase SOC is mostly on managed agricultural lands. If we consider 4 per mille in the top 1m of global agricultural soils, SOC sequestration is between 2-3 Gt C year− 1, which effectively offset 20–35% of global anthropogenic greenhouse gas emissions. As a strategy for climate change mitigation, soil carbon sequestration buys time over the next ten to twenty years while other effective sequestration and low carbon technologies become viable. The challenge for cropping farmers is to find disruptive technologies that will further improve soil condition and deliver increased soil carbon. Progress in 4 per mille requires collaboration and communication between scientists, farmers, policy makers, and marketeers.