Application des techniques physiques, géochimiques et isotopiques pour l'évaluation de l'infiltration sous climat tempéré

Depuis plusieurs années, la Zone Non Saturée d'une parcelle expérimentale au nord de l'Italie (plaine du Pô) a fait l'objet de nombreuses études sur les caractéristiques physiques et géologiques du milieu, ainsi que sur les modalités du mouvement des eaux d'infiltration. Le site a été équipé de 6 tensiomètres à mercure, 6 bougies poreuses pour l'échantillonnage de l'eau et d'un tube d'accès pour la sonde à neutrons.L'application des différentes méthodes d'évaluation a fourni, pour la période d'étude (Septembre 1994-Août 1995), des valeurs de l'infiltration sensiblement différentes. La méthode physique, basée sur le calcul du bilan hydrique annuel, et considérant le sol comme un unique réservoir monocouche, a indiqué que 19% du total des précipitations arrive à s'infiltrer. D'autre part, un modèle de simulation intégrant les caractéristiques hydrodynamiques du sol a permis d'évaluer la recharge à 29% des précipitations annuelles. Le calcul de la répartition de la teneur en eau sur le profil porte sur la description des fluctuations temporelles du plan de flux nul, en relation avec les épisodes pluvieux et l'intensité de l'évaporation.La méthode géochimique du "profil en ions conservés" entre l'eau de pluie et du sol a permis, quant à elle, d'évaluer la lame d'eau infiltrée à environ 12% des précipitations annuelles. La composition isotopique des eaux extraites du sol manifeste un enrichissement global en isotopes lourds (2H et 18O) par rapport aux eaux météoriques, conséquence d'une évaporation intense. L'infiltration semble être de type "piston flow" dispersif. Elle suit, seulement pendant l'hiver, un flux où la composante convective dans la microporosité est prédominante sur la composante diffusive qui a lieu, de préférence, dans la macroporosité.In groundwater management, it is necessary to define water movement, evaluate infiltration and evapotranspiration rates, and quantify the physico-chemical evolution of transported solutes throughout the unsaturated zone (UZ). Traditionally, in temperate regions, recharge rate is evaluated by the comparison between physical methods (based on direct measurements of hydrological parameters with lysimeters, tensiometers and neutron gauges) and geochemical approaches (conservative ions, stable isotope profiles and artificial tracers).In the Po Plain (Northern Italy) intensive agricultural irrigation and overexploitation of groundwater profoundly affect the quality and availability of shallow groundwater resources. The region has been intensively cultivated with corn and rice during the last 5 centuries. Irrigation canals have been constructed in order to distribute water from alpine rivers to areas more favourable to agriculture. In the past, only the water balance method has been applied to obtain recharge rates in these situations.An experimental field site has been operational since 1987 in the ENEA-EUREX Nuclear Centre of Saluggia. The experimental plot represents an unsaturated zone in fluvio-glacial deposits (Holocene) of the Dora Baltea River, formed by gravel and sand, interlayered with silt levels. The water table is usually at a depth of 200 cm but it varies as a function of the river level. The objectives of the present study were to describe water movement throughout the UZ and to evaluate infiltration and evapotranspiration rates using different physico-chemical methodologies. The Saluggia plot was equipped with six tensiometers, a neutron gauge hole and 6 porous cups, up to a depth of 160 cm.During 10 years of monitoring, the most favourable period for understanding infiltration processes and water movement through the UZ is September 1994 - August 1995. This period is characterised by an exceptional rain event (300 mm in 48 hours), followed by a river flood. Water samples collected with porous cups at various depths have been analysed for chemistry and stable isotope composition, together with rainfall and Dora Baltea River water.In October 1994 (beginning of the rainy period) and May 1995 (beginning of the dry period) soil samples were collected at different depths and water was extracted under vacuum conditions. Stable isotope analyses were performed on extracted waters. Soil samples were also analysed for granulometry, chemical and mineralogical composition.Reducing soil to an unique monolayer aquifer, the water balance method suggests that only 19% of the total precipitation infiltrates, whereas a simulation model taking into account soil hydrodynamic characteristics estimates an infiltration rate of 29% of the rainfall. The position of the Zero Flux Plane (ZFP) fluctuates seasonally between the surface and the maximum studied depth, as a consequence of precipitation events and evaporation fluxes. In some periods, the ZFP is level with the water table and direct discharge may occur.Measurements of the stable isotopic composition (δ2H and δ18O) of soil water allows a quantitative estimate of direct groundwater discharge. On a δ2H versusδ18O plot, pore waters from the UZ have an isotopic composition that differs from that of the majority of groundwater samples, plotting below the local rain water line and indicating some degree of evaporation during the recharge process. The isotopic enrichment is particularly significant at the evaporation front, suggesting that pore water in soil reflects a different recharge regime from those of the regional ground waters. Water isotope and solute composition were substantially modified from their original composition during the infiltration process within the soil, via mechanisms such as anion exchange with soil particles, salt precipitation/dissolution or isotopic fractionation.Arial recharge was also evaluated using the depth distribution of a conservative solute. Assuming that chloride is derived from precipitation alone, Cl- content in soil and in rain water suggests that 12% of total rainfall infiltrates. Therefore, the recharge rate is estimated to be less than 100 mm/a. These data are in agreement with other results obtained by the chloride concentration profile method, in areas of the Po Valley, but are considerably different from those evaluated by the traditional physical methods

Validating the regional estimates of changes in soil organic carbon by using the data from paired-sites: the case study of Mediterranean arable lands

BACKGROUND: Legacy data are unique occasions for estimating soil organic carbon (SOC) concentration changes and spatial variability, but their use showed limitations due to the sampling schemes adopted and improvements may be needed in the analysis methodologies. When SOC changes is estimated with legacy data, the use of soil samples collected in different plots (i.e., non-paired data) may lead to biased results. In the present work, N = 302 georeferenced soil samples were selected from a regional (Sicily, south of Italy) soil database. An operational sampling approach was developed to spot SOC concentration changes from 1994 to 2017 in the same plots at the 0-30 cm soil depth and tested. RESULTS: The measurements were conducted after computing the minimum number of samples needed to have a reliable estimate of SOC variation after 23 years. By applying an effect size based methodology, 30 out of 302 sites were resampled in 2017 to achieve a power of 80%, and an α = 0.05. A Wilcoxon test applied to the variation of SOC from 1994 to 2017 suggested that there was not a statistical difference in SOC concentration after 23 years (Z = - 0.556; 2-tailed asymptotic significance = 0.578). In particular, only 40% of resampled sites showed a higher SOC concentration than in 2017. CONCLUSIONS: This finding contrasts with a previous SOC concentration increase that was found in 2008 (75.8% increase when estimated as differences of 2 models built with non-paired data), when compared to 1994 observed data (Z = - 9.119; 2-tailed asymptotic significance < 0.001). This suggests that the use of legacy data to estimate SOC concentration dynamics requires soil resampling in the same locations to overcome the stochastic model errors. Further experiment is needed to identify the percentage of the sites to resample in order to align two legacy datasets in the same area

Evaluation of total and bioavailable heavy metals and other soilrelated variables in a rice paddy after the application of defecation lime

A two-year experiment was carried out in a paddy field to investigate the effects of the use of defecation lime derived from treated sewage sludge on soil total and soil phytoavailable heavy metals concentration. Heavy metals concentration was determined also in raw rice. Four treatments were arranged in a completely randomized block design: not fertilised (T0), organic fertilisation + chemical fertilisers (T1), defecation lime + chemical fertilisers (T2), defecation lime at pre-sowing (T3). For T3, the pH value increased significantly at the end of the second year, increasing from 5.8 to 6.11. T3 resulted in the highest soil organic carbon content (9.4 g kg-1), suggesting the potential of defecation lime both as soil corrective material and soil amendment. The application of defecation lime in the paddy field did not result in an increased phytoavailable amount of heavy metals in soil

Analisi del contenuto idrico del suolo per due differenti sistemi di irrigazione

L\u2019esigenza di attuare interventi mirati alla razionalizzazione della risorsa idrica \ue8 avvertita in modo specifico nel comparto agricolo, in considerazione dei notevolissimi volumi di acqua richiesti per il compimento del ciclo produttivo delle coltivazioni. La scelta del sistema di irrigazione risulta determinante per il contenimento delle perdite e il miglioramento dell\u2019efficienza d\u2019irrigazione. A tal proposito \ue8 stata condotta una sperimentazione in Pianura Padana su due appezzamenti per confrontare due differenti sistemi irrigui: per gravit\ue0 tramite scorrimento superficiale, e per aspersione con pivot ad ala imperniata. Il monitoraggio dei contenuti idrici \ue8 stato eseguito a diverse profondit\ue0, sia con un metodo diretto e discontinuo (metodo gravimetrico), sia con metodo indiretto e continuo, che accoppia la misura tensiometrica in campo, allo studio della curva di ritenzione idrica in laboratorio. La prova di campo ha dimostrato una maggiore perdita per percolazione nel sistema a scorrimento, confermando la bassa efficienza del metodo stesso e la necessit\ue0 di apportare maggiori volumi complessivi

Tecnica di misura dei fenomeni di ruscellamento superficiale

Il suolo \ue8 una risorsa non rinnovabile capace di assicurare funzioni essenziali non solo a livello ambientale ma anche sociale ed economico, assumendo quindi un ruolo centrale nel contesto di sostenibilit\ue0 dell\u2019agricoltura. Tuttavia il suolo \ue8 soggetto ad un continuo degrado dovuto in particolare al fenomeno dell\u2019erosione che non solo ne influenza negativamente le propriet\ue0 nutritive ma diventa una potenziale fonte di inquinamento per le acque superficiali. I fenomeni erosivi sono influenzati da notevoli fattori che il pi\uf9 delle volte vengono meglio descritti se studiati a scala di campo, piuttosto che a piccola scala. Inoltre gli alti costi degli strumenti e la quantit\ue0 enorme di ruscellato limitano il pi\uf9 delle volte il numero di siti che possono essere studiati. Sono stati quindi sperimentati strumenti, per parcelle di pi\uf9 ampia superficie, che permettono di ripartire l\u2019acqua ed il ruscellato e di ridurre in questo modo il campione raccolto mantenendolo rappresentativo. In questo lavoro viene presentata l\u2019applicazione pratica di uno di questi strumenti di misura opportunamente adattato che permette con ampia soluzione temporale di monitorare i fenomeni di ruscellamento superficiale a scala di campo

The nitrification inhibitor Vizura&#174; reduces N&#8322;O emissions when added to digestate before injection under irrigated maize in the Po Valley (Northern Italy)

The agricultural area in the Po Valley is prone to high nitrous oxide (N\u2082O) emissions as it is characterized by irrigated maize-based cropping systems, high amounts of nitrogen supplied, and elevated air temperature in summer. Here, two monitoring campaigns were carried out in maize fertilized with raw digestate in a randomized block design in 2016 and 2017 to test the effectiveness of the 3, 4 DMPP inhibitor Vizura\uae on reducing N2O-N emissions. Digestate was injected into 0.15 m soil depth at side-dressing (2016) and before sowing (2017). Non-steady state chambers were used to collect N\u2082O-N air samples under zero N fertilization (N0), digestate (D), and digestate + Vizura\uae (V). Overall, emissions were significantly higher in the D treatment than in the V treatment in both 2016 and 2017. The emission factor (EF, %) of V was two and four times lower than the EF in D in 2016 and 2017, respectively. Peaks of NO\u2083-N generally resulted in N\u2082O-N emissions peaks, especially during rainfall or irrigation events. The water-filled pore space (WFPS, %) did not differ between treatments and was generally below 60%, suggesting that N\u2082O-N emissions were mainly due to nitrification rather than denitrification

Stima delle emissioni di NH3 con l&apos;uso di modelli a dispersione

Il problema ambientale e gestionale della volatilizzazione di ammoniaca (NH3) ricopre un ruolo sostanziale a causa dell'effetto negativo di tale gas su suolo, acque e stato nutrizionale delle colture. La misura dei flussi di NH3 a scala di campo \ue8 resa difficoltosa dalla rapidit\ue0 di reazione in atmosfera della molecola. In questo lavoro viene presentata una metodologia per quantificare i rilasci di NH3 a scala di campo basata sull\u2019impego di modelli a dispersione. Questi modelli sono in grado di caratterizzare il trasporto degli inquinanti in atmosfera sulla base della misura della turbolenza atmosferica ad alta frequenza e sulla misura delle concentrazioni del gas in analisi con campionatori a diffusione passiva a lunga esposizione. La durata dell\u2019esposizione dei campionatori ed il suo effetto sulla stima del flusso \ue8 stata discussa attraverso una prova di campo con spandimento superficiale di liquame bovino