Multiscale Soil Salinity Assessment at the Southern Margin of the Venice Lagoon, Italy

Saltwater intrusion affects many coastlands around the world contaminating fresh-groundwater and decreasing soil quality. In order to manage saline soils one should understand the spatiotemporal dynamics of salinity in the soil profile and its spatial variability at field scale. In the last decades, soil and pore-water salinity have been assessed using geophysical techniques, most commonly with the use of apparent electrical conductivity (ECa) measurements. At point-scale, pore-water salinity can be estimated once its relationship with ECa, soil properties, and water content is understood. Moreover, most sensors for water content estimation normally provide biased readings in saline conditions and in soil with high clay and organic carbon contents. At field-scale proximal-sensing can be used to characterize large portions of land from a relatively small number of soil samples. Sometimes, characterizing salinity is however not sufficient to understand crop yield spatial variability, which can be also influenced by other soil properties. Understanding the influence of salinity and other soil properties on crop productivity can be useful in the identification of areas that can be managed site-specifically. The general aim of this dissertation is to evaluate some sensor-based methodologies for monitoring and characterizing salinity and other related soil properties both at point- and field-scale. In particular, at point-scale the dissertation will deal with the issues regarding the use of capacitive-resistive technology for water content and pore-water salinity estimation. At field-scale some methodologies will be proposed in order to characterize the spatial variability of salinity and other soil properties influencing maize (Zea mais L.) yield using soil proximal-sensing. All the material presented in this manuscript regard the soils of an area affected by saltwater intrusion located at the southern edge of the Venice Lagoon (Italy). The dissertation is structured in five chapters. The first one includes a review on commonly used methodologies for point- and field-scale salinity assessment. An overview on the environmental issues concerning the coastland at the southern margin of the Venice Lagoon is also presented. The second chapter deals with the calibration of a low-cost capacitance-resistance probe for simultaneous monitoring of soil water content and salinity. In the third chapter an ECa-directed soil sampling scheme optimization procedure is proposed. The forth chapter analyzes maize yield as a function of soil chemical and physical properties and investigates on the use of soil-proximal sensing correlated to soil spatial variability for site-specific management units. The final chapter presents the general conclusions of the work

Robot-assisted Soil Apparent Electrical Conductivity Measurements in Orchards

Soil apparent electrical conductivity (ECa) is a vital metric in Precision Agriculture and Smart Farming, as it is used for optimal water content management, geological mapping, and yield prediction. Several existing methods seeking to estimate soil electrical conductivity are available, including physical soil sampling, ground sensor installation and monitoring, and the use of sensors that can obtain proximal ECa estimates. However, such methods can be either very laborious and/or too costly for practical use over larger field canopies. Robot-assisted ECa measurements, in contrast, may offer a scalable and cost-effective solution. In this work, we present one such solution that involves a ground mobile robot equipped with a customized and adjustable platform to hold an Electromagnetic Induction (EMI) sensor to perform semi-autonomous and on-demand ECa measurements under various field conditions. The platform is designed to be easily re-configurable in terms of sensor placement; results from testing for traversability and robot-to-sensor interference across multiple case studies help establish appropriate tradeoffs for sensor placement. Further, a developed simulation software package enables rapid and accessible estimation of terrain traversability in relation to desired EMI sensor placement. Extensive experimental evaluation across different fields demonstrates that the obtained robot-assisted ECa measurements are of high linearity compared with the ground truth (data collected manually by a handheld EMI sensor) by scoring more than $90\%$ in Pearson correlation coefficient in both plot measurements and estimated ECa maps generated by kriging interpolation. The proposed robotic solution supports autonomous behavior development in the field since it utilizes the ROS navigation stack along with the RTK GNSS positioning data and features various ranging sensors.Comment: 15 pages, 16 figure

Time course of biochemical, physiological, and molecular responses to field-mimicked conditions of drought, salinity, and recovery in two maize lines

Drought and salinity stresses will have a high impact on future crop productivity, due to climate change and the increased competition for land, water, and energy. The response to drought (WS), salinity (SS), and the combined stresses (WS+SS) was monitored in two maize lines: the inbred B73 and an F1 commercial stress-tolerant hybrid. A protocol mimicking field progressive stress conditions was developed and its effect on plant growth analyzed at different time points. The results indicated that the stresses limited growth in the hybrid and arrested it in the inbred line. In SS, the two genotypes had different ion accumulation and translocation capacity, particularly for Na+ and Cl 12. Moreover, the hybrid perceived the stress, reduced all the analyzed physiological parameters, and kept them reduced until the recovery. B73 decreased all physiological parameters more gradually, being affected mainly by SS. Both lines recovered better from WS than the other stresses. Molecular analysis revealed a diverse modulation of some stress markers in the two genotypes, reflecting their different response to stresses. Combining biochemical and physiological data with expression analyses yielded insight into the mechanisms regulating the different stress tolerance of the two lines

Dynamic management zones for irrigation scheduling

Irrigation scheduling decision-support tools can improve water use efficiency by matching irrigation recommendations to prevailing soil and crop conditions within a season. Yet, little research is available on how to support real-time precision irrigation that varies within-season in both time and space. We investigate the integration of remotely sensed NDVI time-series, soil moisture sensor measurements, and root zone simulation forecasts for in-season delineation of dynamic management zones (MZ) and for a variable rate irrigation scheduling in order to improve irrigation scheduling and crop performance. Delineation of MZ was conducted in a 5.8-ha maize field during 2018 using Sentinel-2 NDVI time-series and an unsupervised classification. The number and spatial extent of MZs changed through the growing season. A network of soil moisture sensors was used to interpret spatiotemporal changes of the NDVI. Soil water content was a significant contributor to changes in crop vigor across MZs through the growing season. Real-time cluster validity function analysis provided in-season evaluation of the MZ design. For example, the total within-MZ daily soil moisture relative variance decreased from 85% (early vegetative stages) to below 25% (late reproductive stages). Finally, using the Hydrus-1D model, a workflow for in-season optimization of irrigation scheduling and water delivery management was tested. Data simulations indicated that crop transpiration could be optimized while reducing water applications between 11 and 28.5% across the dynamic MZs. The proposed integration of spatiotemporal crop and soil moisture data can be used to support management decisions to effectively control outputs of crop × environment × management interactions.Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. This study was supported by the European Commission Horizon 2020 Programme for Research and Innovation (H2020) in the context of the Marie Sklodowska-Curie Research and Innovation Staff Exchange (RISE) action (ACCWA project, grant agreement no.: 823965). This study was also funded by the project ‘Low Input Sustainable Agriculture (LISA)’ under the Operational program FEDER for Catalonia 2014‐2020 RIS3CAT (http://www.lisaproject.cat/introduction/).Peer ReviewedPostprint (author's final draft

The Significance of Resorption During Anoxic Mobilization of Phosphorus

Phosphorus has a fundamental role in the regulation of biotic cycles in both aquatic and terrestrial environments. Phosphorus is in fact the limiting nutrient for plants in the majority of the cases. Phosphorus has been historically used in huge amounts to improve agricultural crops production, and this use has had some implications on environment ealth

Multiscale Soil Salinity Assessment at the Southern Margin of the Venice Lagoon, Italy

Saltwater intrusion affects many coastlands around the world contaminating fresh-groundwater and decreasing soil quality. In order to manage saline soils one should understand the spatiotemporal dynamics of salinity in the soil profile and its spatial variability at field scale. In the last decades, soil and pore-water salinity have been assessed using geophysical techniques, most commonly with the use of apparent electrical conductivity (ECa) measurements. At point-scale, pore-water salinity can be estimated once its relationship with ECa, soil properties, and water content is understood. Moreover, most sensors for water content estimation normally provide biased readings in saline conditions and in soil with high clay and organic carbon contents. At field-scale proximal-sensing can be used to characterize large portions of land from a relatively small number of soil samples. Sometimes, characterizing salinity is however not sufficient to understand crop yield spatial variability, which can be also influenced by other soil properties. Understanding the influence of salinity and other soil properties on crop productivity can be useful in the identification of areas that can be managed site-specifically. The general aim of this dissertation is to evaluate some sensor-based methodologies for monitoring and characterizing salinity and other related soil properties both at point- and field-scale. In particular, at point-scale the dissertation will deal with the issues regarding the use of capacitive-resistive technology for water content and pore-water salinity estimation. At field-scale some methodologies will be proposed in order to characterize the spatial variability of salinity and other soil properties influencing maize (Zea mais L.) yield using soil proximal-sensing. All the material presented in this manuscript regard the soils of an area affected by saltwater intrusion located at the southern edge of the Venice Lagoon (Italy). The dissertation is structured in five chapters. The first one includes a review on commonly used methodologies for point- and field-scale salinity assessment. An overview on the environmental issues concerning the coastland at the southern margin of the Venice Lagoon is also presented. The second chapter deals with the calibration of a low-cost capacitance-resistance probe for simultaneous monitoring of soil water content and salinity. In the third chapter an ECa-directed soil sampling scheme optimization procedure is proposed. The forth chapter analyzes maize yield as a function of soil chemical and physical properties and investigates on the use of soil-proximal sensing correlated to soil spatial variability for site-specific management units. The final chapter presents the general conclusions of the work.L’intrusione salina interessa molte zone costiere del mondo con effetti negativi sulla qualità dell’acqua di falda e del suolo. Per gestire i problemi di salinità è necessario capirne le dinamiche temporali a livello di profilo di suolo e la variabilità spaziale a scala di campo. Tecniche geofisiche, in particolare l’utilizzo della conducibilità elettrica apparente (ECa), sono state utilizzate negli ultimi decenni per stimare la salinità del suolo e della soluzione circolante. A scala puntuale la bontà delle misure di salinità della soluzione circolante è legata alla giusta interpretazione del rapporto che la lega ad ECa, alle caratteristiche del suolo e al contenuto idrico. Inoltre, i sensori che misurano l’umidità del suolo spesso forniscono misure falsate in suoli salini e con alto contenuto di argilla e/o sostanza organica. A scala di campo il proximal-sensing può essere utile per caratterizzare vaste porzioni di territorio a partire da un numero relativamente ridotto di campioni di suolo. Spesso la caratterizzazione della salinità non è sufficiente per capire la variabilità spaziale delle rese colturali, che può essere influenzata da altre caratteristiche del suolo. Capendo come la salinità e altre proprietà del suolo influenzano la produttività agraria può essere utile per identificare delle aree in cui apportare interventi agronomici sito-specifici. L’obiettivo generale di questo lavoro è valutare delle metodologie per monitorare e caratterizzare la salinità del suolo ed altri parametri chimico-fisici del suolo ad essa legati, con l’ausilio di sensori, sia a scala puntuale che di campo. In particolare a scala puntuale si affrontano le problematiche relative all’utilizzo di sensoristica capacitivo-resistiva per stimare il contenuto volumetrico e la salinità della soluzione circolante. Mentre a scala di campo si propongono delle metodologie per caratterizzare la variabilità spaziale della salinità del suolo e di altre proprietà che influenzano la resa di Zea mais L. con l’utilizzo di tecniche di proximal-sensing del suolo. Questa tesi riguarda i suoli di un’area di studio interessata da intrusione salina, al margine meridionale della Laguna di Venezia. La tesi è strutturata in cinque capitoli. Il primo include una review sulla metodologia comunemente usata per caratterizzare la salinità del suolo con metodi geofisici sia a scala puntuale che di campo. È inoltre presentata una panoramica introduttiva sulle problematiche ambientali relative alla zona a sud della Laguna di Venezia. Il secondo capitolo si concentra sulla calibrazione di una sonda (low-cost) capacitivo-resistiva da utilizzare per stime in continuo di contenuto idrico volumetrico e salinità della soluzione circolante. Il terzo capitolo propone una metodologia per ottimizzare schemi di campionamento del suolo sulla base della variabilità spaziale di misure geofisiche. Il quarto capitolo analizza la variabilità spaziale della resa colturale in funzione delle proprietà chimico-fisiche del suolo e propone l’utilizzo di dati di proximal-sensing del suolo ad esse correlati per identificare delle aree di gestione omogenee. Infine, l’ultimo capitolo riporta le conclusioni generali e delle note conclusive sui lavori presentati nella tesi

Simultaneous Monitoring of Soil Water Content and Salinity with a Low-Cost Capacitance-Resistance Probe

Capacitance and resistivity sensors can be used to continuously monitor soil volumetric water content (θ) and pore-water electrical conductivity (ECp) with non-destructive methods. However, dielectric readings of capacitance sensors operating at low frequencies are normally biased by high soil electrical conductivity. A procedure to calibrate capacitance-resistance probes in saline conditions was implemented in contrasting soils. A low-cost capacitance-resistance probe (ECH2O-5TE, 70 MHz, Decagon Devices, Pullman, WA, USA) was used in five soils at four water contents (i.e., from dry conditions to saturation) and four salinity levels of the wetting solution (0, 5, 10, and 15 dS·m−1). θ was accurately predicted as a function of the dielectric constant, apparent electrical conductivity (ECa), texture and organic carbon content, even in high salinity conditions. Four models to estimate pore-water electrical conductivity were tested and a set of empirical predicting functions were identified to estimate the model parameters based on easily available soil properties (e.g., texture, soil organic matter). The four models were reformulated to estimate ECp as a function of ECa, dielectric readings, and soil characteristics, improving their performances with respect to the original model formulation. Low-cost capacitance-resistance probes, if properly calibrated, can be effectively used to monitor water and solute dynamics in saline soils

Hydrogeochemical evidence of seawater intrusion: a case study in Venice farmland

Saltwater contamination seriously affects groundwater quality and land productivity of coastal farmland along the Venice lagoon, Italy. Characterizing seawater intrusion dynamics represents a fundamental step to better understand its effect on soil and groundwater quality and in turn, conceive mitigation strategies. To this end, a three-year study was conducted in an experimental field bounding the southern Venice Lagoon. Volumetric water content, soil matric potential and apparent electrical conductivity (ECa) were monitored by five automatic monitoring stations at four depths (0.1, 0.3, 0.5 and 0.7 m). Groundwater electrical conductivity (EC) and depth to the water table were measured at the five stations. In addition, soil pore water at the four depths and borehole groundwater samples were collected periodically and analyzed for chemical composition. Physical and chemical analyses of the soil profiles were also carried out. Relationships between Cl-, Na+, Mg2+, Ca2+, K+, SO42-, Br- ionic concentrations, EC and soil characteristics (e.g. texture, EC1:2, exchangeable cations) were calculated by Pearson and Spearman correlation. Kruskal Wallis test was performed to test the five monitoring stations. Moreover, specific molar ratios (Cl/Br, Br/Cl, Na/Cl and K/Cl) were calculated in order to identify the main drivers affecting salinity in the field. EC and ionic concentrations showed high variability across the monitoring stations and between the different sampling dates (e.g. groundwater EC ranged between 0.33 and 17.46 dS/m). Higher EC and ionic concentration values were observed during upward soil water movement, while values were lower during percolation events (e.g. maximum Cl- concentrations were 9227.3 mg/l and 3436.1 mg/l, respectively). An high correlation resulted between Na+ and Cl- ionic concentrations and EC data in four out of the five monitoring stations (r values between 0.82 and 0.92). In addition, Kruskal Wallis test showed a significant difference between EC and chemical data sampled at the five monitoring stations and different soil depths. These results allow to conclude that soil and water salinity originated from different processes such as seawater intrusion and deep brines upcoming. Understanding salinization sources would enable the definition of a mitigation strategy able to enhance land productivity and water quality

Simultaneous Monitoring of Soil Water Content and Salinity with a Low-Cost Capacitance-Resistance Probe

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