Emanuele Lugato

Surface albedo following biochar application in durum wheat

The agronomic use of charcoal from biomass pyrolysis (biochar) represents an interesting option for increasing soil fertility and sequestering atmospheric CO2. However, before moving toward large-scale biochar applications, additional research must evaluate all possible land‐atmosphere feedbacks. Despite the increasing number of studies investigating the effect of biochar on soil physical, chemical and biological properties, only a few have been done on surface albedo variations on agricultural lands. The present work had the aim of characterizing the annual albedo cycle for a durum wheat crop in Central Italy, by means of a spectroradiometer measurement campaign. Plots treated with biochar, at a rate of 30‐60 t ha 1 , showed a surface albedo decrease of up to 80% (after the application) with respect to the control in bare soil conditions, while this difference tended to decrease during the crop growing season, because of the prevailing effect of canopy development on the radiometer response. After the post-harvesting tillage, the soil treated with biochar again showed a lower surface albedo value (<20‐26% than the control), while the measurements taken in the second year after application suggested a clear decrease of biochar influence on soil color. The modeling of the surface energy balance highlighted changes in the partitioning of heat fluxes and in particular a substantial increase of ground heat fluxes on an annual basis.

An assessment of the global impact of 21st century land use change on soil erosion

Human activity and related land use change are the primary cause of accelerated soil erosion, which has substantial implications for nutrient and carbon cycling, land productivity and in turn, worldwide socio-economic conditions. Here we present an unprecedentedly high resolution (250 × 250 m) global potential soil erosion model, using a combination of remote sensing, GIS modelling and census data. We challenge the previous annual soil erosion reference values as our estimate, of 35.9 Pg yr−1 of soil eroded in 2012, is at least two times lower. Moreover, we estimate the spatial and temporal effects of land use change between 2001 and 2012 and the potential offset of the global application of conservation practices. Our findings indicate a potential overall increase in global soil erosion driven by cropland expansion. The greatest increases are predicted to occur in Sub-Saharan Africa, South America and Southeast Asia. The least developed economies have been found to experience the highest estimates of soil erosion rates.Human activity and related land use change are the primary cause of soil erosion. Here, the authors show the impacts of 21st century global land use change on soil erosion based on an unprecedentedly high resolution global model that provides insights into the mitigating effects of conservation agriculture.

An energy‐biochar chain involving biomass gasification and rice cultivation in Northern Italy

The competing demand for food and bioenergy requires new solutions for the agricultural sector as, for instance, the coupling of energy production from gasification technology and the application of the resulting biochar as soil amendment. A prerequisite for the implementation of this strategy is the scale‐specific assessment of both the energetic performance and of the impacts in terms of greenhouse gases (GHG) emission and crop responses. This study considered the gasification process developed by Advanced Gasification Technology (AGT, Italy), which is a fixed‐bed, down‐draft, open core, compact gasifier, having 350 kW of nominal electric capacity (microgeneration); this gasifier uses biomass feedstock deriving from agricultural/forest products and byproducts. In this study, the resulting biochar, derived from conifer wood chips of mountain forestry management in North‐western Italy, was applied to a nearby paddy rice field, located in the largest rice agricultural area of Europe. We performed a Life Cycle Analysis (LCA) adapting the BEAT2 model specifically focusing on the GHG balance of the supply chain, from the forestry management to the field distribution of the resulting biochar. The results indicated that the gasification stage had the highest impact in the supply chain in terms of emissions, but net emissions allocated to biochar were always negative (ranging between −0.54 and −2.1 t CO2e t−1 biochar), hypothesizing two scenarios of 32% and 7.3% biochar mineralization rate in soil, over a time period of 100 years. Finally, biochar had a marginal but positive effect on rice yield, thus increasing the sustainability of this energy‐biochar chain.

Mitigation potential of soil carbon management overestimated by neglecting N 2 O emissions

International initiatives such as the ‘4 per 1000’ are promoting enhanced carbon (C) sequestration in agricultural soils as a way to mitigate greenhouse gas emissions1. However, changes in soil organic C turnover feed back into the nitrogen (N) cycle2, meaning that variation in soil nitrous oxide (N2O) emissions may offset or enhance C sequestration actions3. Here we use a biogeochemistry model on approximately 8,000 soil sampling locations in the European Union4 to quantify the net CO2 equivalent (CO2e) fluxes associated with representative C-mitigating agricultural practices. Practices based on integrated crop residue retention and lower soil disturbance are found to not increase N2O emissions as long as C accumulation continues (until around 2040), thereafter leading to a moderate C sequestration offset mostly below 47% by 2100. The introduction of N-fixing cover crops allowed higher C accumulation over the initial 20 years, but this gain was progressively offset by higher N2O emissions over time. By 2060, around half of the sites became a net source of greenhouse gases. We conclude that significant CO2 mitigation can be achieved in the initial 20–30 years of any C management scheme, but after that N inputs should be controlled through appropriate management.Agricultural soils can be targeted for carbon (C) sequestration. Research considering C and nitrogen (N) dynamics confirms that significant CO2 mitigation can be achieved, but after 20–30 years N inputs also need controlling to prevent the C sequestration being offset by N2O emissions.

Long-term pan evaporation observations as a resource to understand the water cycle trend: case studies from Australia

Abstract Acceleration of the global water cycle over recent decades remains uncertain because of the high inter-annual variability of its components. Observations of pan evaporation (Epan), a proxy of potential evapotranspiration (ETp), may help to identify trends in the water cycle over long periods. The complementary relationship (CR) states that ETp and actual evapotranspiration (ETa) depend on each other in a complementary manner, through land–atmosphere feedbacks in water-limited environments. Using a long-term series of Epan observations in Australia, we estimated monthly ETa by the CR and compared our estimates with ETa measured at eddy covariance Fluxnet stations. The results confirm that our approach, entirely data-driven, can reliably estimate ETa only in water-limited conditions. Furthermore, our analysis indicated that ETa did not show any significant trend in the last 30 years, while short-term analysis may indicate a rapid climate change that is not perceived in a long-term perspective. Editor Z.W. Kundzewicz; Associate editor D. Gerten Citation Lugato, E., Alberti, G., Gioli. B., Kaplan, J.O., Peressotti, A., and Miglietta, F., 2013. Long-term pan evaporation observations as a resource to understand the water cycle trend: case studies from Australia. Hydrological Sciences Journal, 58 (6), 1287–1296.

Complementing the topsoil information of the Land Use/Land Cover Area Frame Survey (LUCAS) with modelled N2O emissions

Two objectives of the Common Agricultural Policy post-2013 (CAP, 2014–2020) in the European Union (EU) are the sustainable management of natural resources and climate smart agriculture. To understand the CAP impact on these priorities, the Land Use/Cover statistical Area frame Survey (LUCAS) employs direct field observations and soil sub-sampling across the EU. While a huge amount of information can be retrieved from LUCAS points for monitoring the environmental status of agroecosystems and assessing soil carbon sequestration, a fundamental aspect relating to climate change action is missing, namely nitrous oxide (N2O) soil emissions. To fill this gap, we ran the DayCent biogeochemistry model for more than 11’000 LUCAS sampling points under agricultural use, assessing also the model uncertainty. The results showed that current annual N2O emissions followed a skewed distribution with a mean and median values of 2.27 and 1.71 kg N ha-1 yr-1, respectively. Using a Random Forest regression for upscaling the modelled results to the EU level, we estimated direct soil emissions of N2O in the range of 171–195 Tg yr-1 of CO2eq. Moreover, the direct regional upscaling using modelled N2O emissions in LUCAS points was on average 0.95 Mg yr-1 of CO2eq. per hectare, which was within the range of the meta-model upscaling (0.92–1.05 Mg ha-1 yr-1 of CO2eq). We concluded that, if information on management practices would be made available and model bias further reduced by N2O flux measurement at representative LUCAS points, the combination of the land use/soil survey with a well calibrated biogeochemistry model may become a reference tool to support agricultural, environmental and climate policies.

Copper distribution in European topsoils: An assessment based on LUCAS soil survey

Copper (Cu) distribution in soil is influenced by climatic, geological and pedological factors. Apart from geological sources and industrial pollution, other anthropogenic sources, related to the agricultural activity, may increase copper levels in soils, especially in permanent crops such as olive groves and vineyards. This study uses 21,682 soil samples from the LUCAS topsoil survey to investigate copper distribution in the soils of 25 European Union (EU) Member States. Generalized Linear Models (GLM) were used to investigate the factors driving copper distribution in EU soils. Regression analysis shows the importance of topsoil properties, land cover and climate in estimating Cu concentration. Meanwhile, a copper regression model confirms our hypothesis that different agricultural management practices have a relevant influence on Cu concentration. Besides the traditional use of copper as a fungicide for treatments in several permanent crops, the combined effect of soil properties such as high pH, soil organic carbon and clay, with humid and wet climatic conditions favours copper accumulation in soils of vineyards and tree crops. Compared to the overall average Cu concentration of 16.85 mg kg-1, vineyards have the highest mean soil Cu concentration (49.26 mg kg-1) of all land use categories, followed by olive groves and orchards. Gaussian Process Regression (GPR) combined with kriging were used to map copper concentration in topsoils and to evidence the presence of outliers. GPR proved to be performant in predicting Cu concentration, especially in combination with kriging, accounting for 66% of Cu deviance. The derived maps are novel as they include information about the importance of topsoil properties in the copper mapping process, thus improving its accuracy. Both models highlight the influence of land management practices in copper concentration and the strong correlation between topsoil copper and vineyards.

A step towards a holistic assessment of soil degradation in Europe: Coupling on-site erosion with sediment transfer and carbon fluxes

ABSTRACT Soil degradation due to erosion is connected to two serious environmental impacts: (i) on‐site soil loss and (ii) off‐site effects of sediment transfer through the landscape. The potential impact of soil erosion processes on biogeochemical cycles has received increasing attention in the last two decades. Properly designed modelling assumptions on effective soil loss are a key pre‐requisite to improve our understanding of the magnitude of nutrients that are mobilized through soil erosion and the resultant effects. The aim of this study is to quantify the potential spatial displacement and transport of soil sediments due to water erosion at European scale. We computed long‐term averages of annual soil loss and deposition rates by means of the extensively tested spatially distributed WaTEM/SEDEM model. Our findings indicate that soil loss from Europe in the riverine systems is about 15% of the estimated gross on‐site erosion. The estimated sediment yield totals 0.164 ± 0.013 Pg yr−1 (which corresponds to 4.62 ± 0.37 Mg ha−1 yr−1 in the erosion area). The greatest amount of gross on‐site erosion as well as soil loss to rivers occurs in the agricultural land (93.5%). By contrast, forestland and other semi‐natural vegetation areas experience an overall surplus of sediments which is driven by a re‐deposition of sediments eroded from agricultural land. Combining the predicted soil loss rates with the European soil organic carbon (SOC) stock, we estimate a SOC displacement by water erosion of 14.5 Tg yr−1. The SOC potentially transferred to the riverine system equals to 2.2 Tg yr−1 (˜15%). Integrated sediment delivery‐biogeochemical models need to answer the question on how carbon mineralization during detachment and transport might be balanced or even off‐set by carbon sequestration due to dynamic replacement and sediment burial. HIGHLIGHTSWaTEM/SEDEM was applied to simulate soil loss and deposition rates at European scale.Our findings indicate that soil loss in the riverine systems is about 15% of RUSLE2015 estimates.The estimated sediment yield in Europe totals 0.164 ± 0.013 Pg yr−1.We estimate a SOC displacement by water erosion in Europe of 14.5 Tg yr−1.

Cropland and Grassland Management

According to the latest National Inventory, the Italian agricultural sector is a source of GHGs with 34.5 Mt of CO2 eq in 2009, corresponding to 7 % of the total emissions (excluding LULUCF). In particular, more than half (19.1 Mt of CO2 eq) are N2O emissions from soils. Although the national methodology is in accordance with Tier 1 and 2 approaches proposed by the IPCC (2006), still empirical emission factors are used to assess the emission from fertilizer (e.g. 0.0125 kg N2O–N kg−1 N from synthetic fertilizers). Disaggregated data at sub-national level, including models and inventory measurement systems required by higher order methods (i.e. Tier 3), are not available in Italy so far and comparisons with the other two approaches cannot be performed at the moment. Despite the large soil organic carbon pool in the agricultural soils and the recent institutionalization of the ‘National Registry for Carbon sinks’ by a Ministerial Decree on 1st April 2008, the last Italian greenhouse gas Inventory did not report CO2 emissions from the agricultural sector. In this context, this chapter wants to summarize the main outcomes coming from the main long-term experiments present in Italy by integrating experimental and modeling approaches, which can provide national emission rates and a solid base to test and calibrate simulation models to estimate greenhouse gases emissions from Italian agricultural soils. What emerges clearly from the analysis is that the agro-ecosystems may sequester large amount of SOC if appropriate management practices are adopted. Moreover, the use of simulation models calibrated at local level and spatially applied, as done for the Carboitaly project, may certainly reduce the uncertainty of these estimations.