Arianna Facchi

Coupled SVAT–groundwater model for water resources simulation in irrigated alluvial plains

Understanding the interaction between soil, vegetation and atmosphere processes and groundwater dynamics is of paramount importance in water resources planning and management in extensively irrigated alluvial plains. This is the case, for example, of the most important agricultural and industrial area in Italy, the Padana Plain, where intensive exploitation of groundwater for domestic and industrial supply coexists with massive diversions from surface water bodies, providing abundant irrigation to one of the most productive agricultural districts in Europe. The paper presents a simulation system which reproduces the hydrological processes relevant in alluvial irrigated plains. In particular, it allows the evaluation of the distribution of crop water consumption in space and time, as well as simulation of the interaction between recharge and groundwater dynamics. The simulation code is based on the coupling of two models: a conceptual vadose zone model and the groundwater flow model MODFLOW. Additional code was written to provide an interface which performs the explicit coupling in space and time between the two models. A geographical information system (GIS) manages the spatially distributed inputs, parameters and outputs of the system. An application of the package to a large irrigation district, of approximately 700 km2, located in the middle of the Padana Plain, is also discussed in the paper.

An integrated, multisensor system for the continuous monitoring of water dynamics in rice fields under different irrigation regimes

The cultivation of rice, one of the most important staple crops worldwide, has very high water requirements. A variety of irrigation practices are applied, whose pros and cons, both in terms of water productivity and of their effects on the environment, are not completely understood yet. The continuous monitoring of irrigation and rainfall inputs, as well as of soil water dynamics, is a very important factor in the analysis of these practices. At the same time, however, it represents a challenging and costly task because of the complexity of the processes involved, of the difference in nature and magnitude of the driving variables and of the high variety of field conditions. In this paper, we present the prototype of an integrated, multisensor system for the continuous monitoring of water dynamics in rice fields under different irrigation regimes. The system consists of the following: (1) flow measurement devices for the monitoring of irrigation supply and tailwater drainage; (2) piezometers for groundwater level monitoring; (3) level gauges for monitoring the flooding depth; (4) multilevel tensiometers and moisture sensor clusters to monitor soil water status; (5) eddy covariance station for the estimation of evapotranspiration fluxes and (6) wireless transmission devices and software interface for data transfer, storage and control from remote computer. The system is modular and it is replicable in different field conditions. It was successfully applied over a 2-year period in three experimental plots in Northern Italy, each one with a different water management strategy. In the paper, we present information concerning the different instruments selected, their interconnections and their integration in a common remote control scheme. We also provide considerations and figures on the material and labour costs of the installation and management of the system.

Is soil water potential a reliable variable for irrigation scheduling in the case of Peach Orchards

Abstract Monitoring the crop water status of high-value crops such as fruit trees is generally performed through periodic measurements of physiological indicators on leaves or fruits using sophisticated instruments and complex procedures. These measurements are very often difficult to translate into irrigation advice. Soil water potential (SWP), however, is a basic soil water status variable that is correlated with plant water uptake, and it can easily be measured using sensors. Soil water potential can provide useful support for irrigation scheduling at the field scale, thus enhancing water savings in agricultural areas. In this work, we present the results of an experimental study conducted in the 2014 agricultural season on a peach orchard located in Lodi (Northern Italy). The purpose of this study was to evaluate the effects of an irrigation scheduling based on continuous SWP measurements collected at two soil depths (−15 and −35 cm) on the crop water status and the peach production relative to the farmer’s commonly adopted irrigation practice. To answer the question in the title, periodic measurements of physiological parameters such as leaf water potential, stomatal resistance (rs), transpiration (E), and crop water stress index were performed, along with monitoring of fruit size evolution and fruit sugar content at harvest. All of these variables were measured to assess the crop physiological state of the trees subjected to the two different irrigation treatments, with the final objective of determining whether the irrigation scheduling based on SWP measurements compromised the quality and quantity of produced peaches. Although obtained for only one agricultural season, the results showed that no considerably crop water stress occurred, even for the irrigation treatment based on SWP measurements. In particular, the most extreme values of leaf water potential, rs, E, and crop water stress index measured at midday were −2 MPa, 45 s m−1, 1.4 mm h−1 and 0.5, respectively, which are in good agreement with those observed in many studies for well-watered orchards in Mediterranean areas. In conclusion, we can stress that SWP monitoring can be considered to be a reliable alternative to the more costly and time-consuming physiological measurements for the irrigation scheduling of fruit crops such as peach orchards. This approach provides continuous information about the soil water status, thereby preventing plant water stress and reducing irrigation water consumption at the farm scale.

Mapping Soil Water Capacity Through EMI Survey to Delineate Site-Specific Management Units Within an Irrigated Field

Abstract An accurate and high-resolution mapping of soil properties allows optimizing the management of irrigation and fertilization at field scale by applying variable amounts of water and nutrients. Site-specific management (SSM) is fundamental to improve crop yield and to use resources more efficiently, improving environmental sustainability. Adoption of site-specific management practices requires the delineation in the field of subregions with similar soil properties affecting yield (site-specific management units (SSMU)). It is common practice to characterize the spatial variability of soil properties through electromagnetic induction (EMI) surveys to obtain soil electrical conductivity (EC) maps that can be used to delineate SSMU. The objectives of this work, carried out over a uniformly drip-irrigated and fertilized maize, were to (i) delineate SSMU from EC maps; (ii) compare the SSMU inferred from measurements with two different EMI sensors; (iii) map the soil-available water-holding capacity (AWC) from EC maps through a regression model between EC and measured AWC; and (iv) evaluate significant differences of crop yield among the SSMU. The EC maps at increasing depths were processed through principal component analysis, and three SSMU were delineated for both EMI sensors using the Management Zone Analyst software. The significant difference in crop yield across the three SSMU, tested through the analysis of variance, suggested that AWC was the main limiting factor in crop yield. This result highlights the importance of a variable-rate irrigation based on SSMU, which could be a solution to save water and increase crop yield.

Use of Spectral and Thermal Imaging Sensors to Monitor Crop Water and Nitrogen Status

High spatial and temporal resolution monitoring methods are the key to improve the efficiency in water and fertilizer input management. In this context, this work presents the set-up and the first results of a greenhouse experiment conducted on two crops with a different canopy geometry (rice and spinach) subjected to four nitrogen treatments. The experiment involves the acquisition of thermal, multispectral and hyperspectral images at three phenological stages for each crop. At each stage, spectral acquisitions are conducted on one-third of the pots, at good water conditions and, later on, at different times after interruption of irrigation. The total number of pots in the experiment is 72 (corresponding to 4 nitrogen levels x 2 crops x 3 phenological stages x 3 replicates). Just after the spectra acquisitions, non-destructive and destructive measurements of variables correlated with the crops nitrogen and water status are conducted. Multivariate regression analysis between the spectra features and measured variables will be used to identify predicting models for the estimation of crop water and nitrogen status. The most significant wavelengths for the detection of water and nitrogen stress could be the subject of a future experimentation in open field conditions using multispectral systems.

Comparing EM38 and Profiler-EMP400 for the Delineation of Homogeneous Management Zones within Agricultural Fields

The improvement in crop yield, both in quantity and quality, depends on the adoption of appropriate management strategies for the agronomic and irrigation practices. The adoption of site-specific (SS) management practices is fundamental, not only to improve crop yield, but also for a more efficient use of resources, increasing the environmental sustainability of the agricultural production The SS management requires the delineation of sub-regions with similar yield limiting factors or similar soil properties affecting yield (Site Specific Management Units – SSMU). It is a common practice in precision agriculture (PA) to characterize the spatial variability of soil properties, measuring the soil electrical conductivity through non-invasive electro-magnetic (EM) sensors to obtain high-resolution soil maps for the delineation of SSMUs. Because of the expanding use in the future of the multi-frequency EM sensors in order to more effectively assess the soil variability, the objective of this work is to compare the measurements collected by Geonics EM38 (the most widely used EM sensor in PA) and GSSI Profiler-EMP400 (a multi-frequency EM sensor) in order to assess their reliability to delineate SSMUs. The data from 2-D electrical resistivity imaging were used to compare the response of the two different sensors to soil variability.