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Layered soils can consist of a thin little permeable upper layer over a more permeable subsoil. There are not many experimental data on the influence of this upper layer on infiltration. The mini-disk infiltrometer set at a pressure head of –3 cm was used to compare infiltration of nearly 40 mm of water in homogeneous loam and clay soil columns with that in columns made by a thin layer (1 and 3 cm) of clay soil over the loam soil. For each run, the Horton infiltration model was fitted to the data and the soil sorptivity was also estimated by considering the complete infiltration run. For the two layered soils, the estimates of initial infiltration rate and decay constant were similar but a thicker upper layer induced 2.4 times smaller final infiltration rates. Depending on the infiltration parameter and the thickness of the upper layer, the layered soils were characterized by 2.2–6.3 times smaller values than the loam soil and 2.2–6.6 higher values than the clay soil. Sorptivity did not differ between the homogeneous clay soil and the layered soil with a thick upper layer and a thin layer was enough to induce a decrease of this hydrodynamic parameter by 2.5 times as compared with that of the homogeneous loam soil. Even a thin upper layer influences appreciably infiltration and hydrodynamic parameters. Layering effects vary with the thickness of the upper layer and the considered parameter. The applied experimental methodology could be used with other soils and soil combinations.

Modeling agricultural systems, from the point of view of saving and optimizing water, is a challenging task, because it may require multiple soil physical and hydraulic measurements to investigate the entire crop cycle. The Beerkan method was proposed as a quick and easy approach to estimate the saturated soil hydraulic conductivity, Ks. In this study, a new complete three-dimensional model for Beerkan experiments recently proposed was used. It consists of thirteen different calculation approaches that differ in estimating the macroscopic capillary length, initial (θi) and saturated (θs) soil water contents, use transient or steady-state infiltration data, and different fitting methods to transient data. A steady-state version of the simplified method based on a Beerkan infiltration run (SSBI) was used as the benchmark. Measurements were carried out on five sampling dates during a single growing season (from November to June) in a long-term experiment in which two soil management systems were compared, i.e., minimum tillage (MT) and no tillage (NT). The objectives of this work were (i) to test the proposed new model and calculation approaches under real field conditions, (ii) investigate the impact of MT and NT on soil properties, and (iii) obtain information on the seasonal variability of Ks and other main soil physical properties (θi, soil bulk density, ρb, and water retention curve) under MT and NT. The results showed that the model always overestimated Ks compared to SSBI. Indeed, the estimated Ks differed by a factor of 11 when the most data demanding (A1) approach was considered by a factor of 4–8, depending on the transient or steady-state phase use, when A3 was considered and by a practically negligible factor of 1.0–1.9 with A4. A relatively higher seasonal variability was detected for θi at the MT than NT system. Under both MT and NT, ρb did not change between November and April but increased significantly until the end of the season. The selected calculation approaches provided substantially coherent information on Ks seasonal evolution. Regardless of the approach, the results showed a temporal stability of Ks at least from early April to June under NT; conversely, the MT system was, overall, more affected by temporal changes with a relative stability at the beginning and middle of the season. These findings suggest that a common sampling time for determining Ks could be set at early spring. Soil management affected the soil properties, because the NT system was significantly wetter and more compact than MT on four out of five dates. However, only NT showed a significantly increasing correlation between Ks and the modal pore diameter, suggesting the presence of a relatively smaller and better interconnected pore network in the no-tilled soil. This study confirms the need to test infiltration models under real field conditions to evaluate their pros and cons. The Beerkan method was effective for intensive soil sampling and accurate field investigations on the temporal variability of Ks. [ABSTRACT FROM AUTHOR]

The main objective of the work is to optimize drip installation depth for Eggplant crop irrigated with surface or subsurface drip irrigation systems to improve irrigation Water Use Effeciency (WUE), by means of field measurements and simulations carried out with Hydrus-2D model. Initially, a comparison between simulated Soil Water Contents (SWC) and the corresponding measured in two plots, in which laterals with coextruded emitters are laid on the soil surface (T0) and at 20 cm depth (T20), respectively. In order to choose the best position of the lateral, the results of different simulation run, carried out by choosing a deeper installation (T45) depth. Simulated SWC’s resulted fairly close to the corresponding measured at different distances from the emitter and therefore the model was able to predict SWC’s in the root zone with values of the Root Mean Square Error generally lower than 4%. This result is consequent to the appropriate schematization of the root distribution, as well as of the root water uptake. The values of WUE associated to the different examined installation depths tend to a very slight increase when the position of the lateral is situated on 20 cm and start to decrease for the higher depths.

Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the world, chiefly caused by the use of highly salinity irrigation water, compounded by excessive evapotranspiration. Given this threat, efficient field assessment methods are needed to monitor the dynamics of soil salinity in salt-affected irrigated lands and evaluate the performance of management strategies. In this study, we report on the results of an irrigation experiment with the main objective of evaluating time-lapse inversion of electromagnetic induction (EMI) data and hydrological modelling in field assessment of soil salinity dynamics. Four experimental plots were established and irrigated 12 times during a two-month period, with water at four different salinity levels (1, 4, 8 and 12dSm-1) using a drip irrigation system. Time-lapse apparent electrical conductivity (σa) data were collected 6 times during the experiment period using a CMD Mini-Explorer. Prior to inversion of time-lapse σa data, a numerical experiment was performed by 2D simulations of the water and solute infiltration and redistribution process. The obtained potential spatio-temporal distributions of water content, solute concentration and bulk electrical conductivity (σb) assisted in understanding of how solute concentration and water content changes during the experiment influence σb distribution as well as optimizing the time-lapse inversion parameters for resolving σb changes in this experiment. Finally, we inverted the time-lapse field σa data and interpreted the results in terms of concentration distributions over time. Our investigation shows that EMI measurements and suitable modelling techniques allow for rapid and non-invasive investigation of spatio-temporal variability in soil salinity over large areas. Their effectiveness and relatively low cost make them appealing for management of water irrigation in salinity-threatened regions of the world. [ABSTRACT FROM AUTHOR]

Grapevine is well adapted to Mediterranean climate where it is commonly cultivated along the slopes in hilly areas.The soil is a primary factor of terroir. Soils with limited water holding capacity can bring to vine water stress, which affects grape and wine quality. Along the slope, heterogeneity of soil physical properties and water flow can allow better soil water status in down- than up-hill soil. In the literature, discrimination between these two factors is often only qualitatively addressed and differences in grape and wine quality between down- and up-hill soil are often attributed to a generic "slope effect".Our aim is to discriminate in a vineyard grown along slopes, the role played by the hydraulic properties from the topographic characteristics in producing differences in soil water availability and therefore differences in grapevine water status, which, in turn, affects physiological responses, growth, yield and grape/wine quality.The experimental site was an "Aglianico" vineyard grown along a 90 m slope (17.7 %) in a hilly area of the Mediterranean environment. The two soil sites, Cambic Calcisol (Up-hill) and Eutric Cambisol (Down-hill), had similar clay loam texture with different hydrological properties. Soil and vine water status, leaf gas exchanges and fluorescence, leaf area index, yield, and grape and wine quality were measured in the up- and down-hill side of the slope in two consecutive years. Hydrus-2D model was used to simulate water flow along the slope to estimate water status in the soil-plant-atmosphere continuum by using the two-year climate data set. We compared the model outputs for the two soil sites with the field experimental measurements. Finally, in order to quantify the effect of the slope steepness on the soil water balance of the two soils, the model was applied to simulate water flow with and without slope.Down-hill soil had higher both soil matric potential and water content than Up-hill soil. Vines at bottom of slope had better leaf water status and higher gas-exchanges rate, photosynthetic efficiency, leaf area index and grape yield than vines at the top. On the contrary, quality of both grape and wine were enhanced in the more stressed up-hill than down-hill vines. Along the two years, Hydrus-2D simulations showed higher soil water availability in the Down- than the Up-hill soil. This result was predominantly caused by the different hydraulic properties between the two site soils, whereas the estimated contribution of both superficial runoff and lateral infiltration (inside soil) along the slope was negligible.In conclusion, the "slope effect" on the soil water status and consequently on the vineyard behaviour, was mainly dominated by soil hydraulic properties rather than the steepness of the slope. [ABSTRACT FROM AUTHOR]

Soil bulk electrical conductivity is being used as a surrogate measure of soil hydraulic variables, such as water content. In this framework, the electromagnetic induction methodology is a fast and non-invasive tool which is very useful for hydrological and agronomic purposes, nevertheless some theoretical and applicative issues are still unsolved. The aim of this study is to detect spatio-temporal dynamic of soil water content from non-invasive and fast electromagnetic induction measurements in two experimental fields located in southern Italy. The first one was on bare soil (Colluvic Regosol) in Valenzano (Bari) and the second on corn cultivation in Acerra (Napoli) (Mollic Vitric Andosol). Both experiments consists of two sub-plots irrigated with water at about 1 and 8 dS m-1. To achieve this goal, the apparent electrical conductivity was measured in the field by means of a CMD MiniExplorer sensor based on the electromagnetic induction (EMI) methodology. The EMI sensor was used with horizontal and vertical dipole orientations in order to measure apparent electrical conductivity at 6 depths (depth range 0.25-1.8 m). TDR field measurements were also performed during the experiments. In addition, laboratory analyses were performed on undisturbed soil samples previously collected in the field in order to define the relationship between the electrical conductivity and the water content. From the collected electromagnetic data, by means of an inversion algorithm performed by TerraEM software, we calculated the bulk electrical conductivity. Then, we retrieved the volumetric water contents by means of the relationship bulk electrical conductivity vs. volumetric water content previously defined in the laboratory. Here we will present some drawbacks and methodological issues encountered during the physical and numerical (inversion algorithm) experiments on two completely different soils. [ABSTRACT FROM AUTHOR]

The assessment of the soil solution salinity is a crucial task in irrigated production systems in the Mediterranean-like climate, where the ecological conditions predispose to salt accumulation within the soils. In this framework, the electromagnetic induction methodology is a fast and non-destructive tool which is very useful for hydrological and agronomic purposes. Nonetheless, the measured apparent conductivity strongly depends on both water content and soil salinity. Hence, in saline soils is not easy to estimate, at the same time, both variables. Our effort was aimed at distinguishing these two contributions affecting the measured electrical conductivity. In an experimental field with corn cultivation located in southern Italy, we sampled undisturbed soil specimens to measure in the laboratory, by means of TDR probes, the variation of the bulk electrical conductivity with varying volumetric water content using non saline water. Then, in the same field, two plots were irrigated with non-saline water and saline water, respectively. The irrigation lasted roughly 6 weeks with one irrigation per week on average. After the last irrigation, we performed several electromagnetic measurements in both plots at 6 depths (depth range 0.25-1.8 m) and with a 1 m spacing till the soil was dry. Then, the same day of the corn harvesting we opened a trench in the saline plot. Soil water content and bulk electrical conductivity were measured by TDR probes along the transect at four depths. Moreover, we sampled the soil at several depths and positions in order to measure in the laboratory the soil solution electrical conductivity. From the electromagnetic data, by means of an inversion procedure performed by TerraEM software, we calculated the bulk electrical conductivity of the non-saline plot. Then, we retrieved the volumetric water contents by means of the relationship bulk electrical conductivity vs. volumetric water content previously measured in the laboratory. Since the field was homogeneous, the obtained water contents of the non-saline plot were compared to the water contents of the saline plot. These last were directly measured in the field at several depths by means of TDR probes in the same day of the electromagnetic measurements. The agreement between the trends of the measured and estimated water content values was very good, but the absolute values were different unless a shift constant that we empirically estimated. Then, since both the volumetric water content and the bulk electrical conductivity were known, we inverted the Rhoades formula to calculate the electrical conductivity of the soil solution. This approach allows to obtain a good estimation of the electrical conductivity of the soil solution and soil water content by coupling very easy and non-destructive electromagnetic field measurements with a simple laboratory calibration performed by TDR. [ABSTRACT FROM AUTHOR]