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The eddy correlation technique was used to investigate the influence of biophysical variables and crop phenological phases on the behaviour of ecosystem carbon fluxes of a maize crop, in two contrasting growing seasons. In 2009, the reduced water supply during the early growing stage limited leaf area expansion, thus negatively affecting canopy photosynthesis. The variability of gross primary production (GPP) and ecosystem respiration (R eco) was mainly explained by seasonal variation of leaf area index (LAI). The seasonal variation of R eco was positively influenced by soil temperatures (T soil) in 2008 but not in 2009. In 2008, a contribution of both autotrophic and heterotrophic components to total R eco could be hypothesized, while during 2009, autotrophic respiration is supposed to be the most important component. Crop phenological phases affected the response of ecosystem fluxes to biophysical drivers.

Aircraft measurements were used to estimate the CO2 emission rates of the city of Rome, assessed against high-resolution inventorial data. Three experimental flights were made, composed of vertical soundings to measure Planetary Boundary Layer (PBL) properties, and circular horizontal transects at various altitudes around the city area. City level emissions and associated uncertainties were computed by means of mass budgeting techniques, obtaining a positive net CO2 flux of 14.7 ± 4.5, 2.5 ± 1.2, and 10.3 ± 1.2 μmol m(-2) s(-1) for the three flights. Inventorial CO2 fluxes at the time of flights were computed by means of spatial and temporal disaggregation of the gross emission inventory, at 10.9 ± 2.5, 9.6 ± 1.3, and 17.4 ± 9.6 μmol m(-2) s(-1). The largest differences between the two dataset are associated with a greater variability of wind speed and direction in the boundary layer during measurements. Uncertainty partitioned into components related to horizontal boundary flows and top surface flow, revealed that the latter dominates total uncertainty in the presence of a wide variability of CO2 concentration in the free troposphere (up to 7 ppm), while it is a minor term with uniform tropospheric concentrations in the study area (within 2 ppm). Overall, we demonstrate how small aircraft may provide city level emission measurements that may integrate and validate emission inventories. Optimal atmospheric conditions and measurement strategies for the deployment of aircraft experimental flights are finally discussed.

Micrometeorological methods for measuring fluxes of gases between the land surface and the atmosphere are non-invasive: in fact, they do not interfere with natural processes of gas exchange. The Micrometeorological Mass Difference (MMD) approach can be used for many environmental monitoring purposes, such as to measure methane and carbon dioxide emission from landfills, methane production by grazing animals, trace gas emission from waste products and from agricultural soils, photosynthesis, and transpiration of plant canopies. The purpose of this study is to adapt the MMD technique, originally developed in Australia, to monitor CO2 and trace gases exchange rate at the plot level. Comparison of different treatments in replicated experiments requires plots of few rather than tens of meters. The tests reported here were performed on a square area (4 m x 4 m) in the meteorological field of the experimental farm of CNR-ISAFOM located in Vitulazio, province of Caserta, Italy (40 degrees 07' N, 14 degrees 50' E, 25 m above sea level) and consisted of the release of pure CO2 at different rates (1.7, 1.3, 0.6 L min(-1)) from a single source on the ground in the center of the experimental area and the consequent measurement of the environmental variables (wind speed and direction, CO2 concentration) at different times at four heights (up to 1.2 m) in order to compute the mass balance according to MMD technique. Measured flow rates well accounted for the mass of CO2 released. A flow underestimation occurred when wind speed dropped below 1.5 m s(-1), in accord with the previous findings obtained in Australia: this happened because anemometers can stall at low speeds, and their measurements are unreliable and because of significant loss of mass from the top of the apparatus. The experimental results were compared with outputs of Computational Fluid Dynamic (CFD) simulations. The commercial CFD package Fluent was used to evaluate performances and sources of errors. According to the experimental and numerical results, the MMD apparatus in our present configuration is suitable to be used for the monitoring of trace gas emissions of experimental plots. Advantages and limits of the present approach are discussed.

Green manuring of legume crops has increased in interest in recent years because of environmental and economic costs of synthetic fertilizers and need of sustainable cropping systems. Climatic conditions can reduce the agronomic and environmental effectiveness of green manuring promoting reactive nitrogen losses, or fostering soil heterotrophic respiration. This study aims to quantify ammonia and nitrous oxide losses, as well as carbon dioxide exchanges following green manuring of faba bean (Vicia faba spp. minor L.) under semi-arid climate conditions, typical of the Mediterranean basin. Ammonia emissions were measured by means of an aerodynamic gradient approach equipped with a multi-channel wet-denuder system (ROSAA), alongside with a concentration-based inverse dispersion modelling assessment. Nitrous oxide losses were measured with an automated chamber system, whereas carbon dioxide and water vapor exchanges were monitored jointly by means of eddy covariance technique. Ammonia volatilization lasted for three weeks and was triggered by the increase of soil water content due to rainfall, occurring 5 days after green manuring. Total emissions were 0.31% of the nitrogen supplied by green manuring (230 kg N ha−1). Nitrous oxide emissions from soil were of low intensity during the measurement period and were directly corelated to the water filled pore space. The biogeochemical model CERES-EGC was validated with the measurements of nitrous oxide, then used to reproduce the dynamic until the sowing of the succeeding crop. Cumulated emissions of nitrous oxide were 1% of the total nitrogen supplied. Soil became a net source both of carbon dioxide and water vapor soon after green manuring, with an emission of 900 kg C-CO 2 ha−1 by heterotrophic respiration (23% of added carbon). In terms of water balance, 19 mm of water evaporated from soil surface, originated from the addition of fresh biomass. Green manuring proved to be a significant agronomic strategy to improve soil fertility, limiting reactive nitrogen and carbon losses to the atmosphere. • Green manure legume crops are a minor source of NH 3 in the atmosphere. • N 2 O emissions are triggered by soil moisture conditions in dry environments. • Fresh biomass stimulates soil heterotrophic respiration and water evaporation. • Green manure legume crops increase nitrogen use efficiency. [ABSTRACT FROM AUTHOR]