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Biochar application to soil can be considered as a means to improve soil quality, thereby optimizing irrigation management and reducing irrigation needs, especially in dryland regions. This paper is aimed at investigating the effect of biochar (BC) on a desert sandy soil (Al Foah, United Arab Emirates) in terms of bulk density, porosity, water retention, plant available water (AWmax), aggregate stability (AS) and specific surface area (BET-SSA). BC was produced from forest biomass (Italy). Soil water retention was measured by the High Energy Moisture Characteristic (HEMC) and by pressure plate measurements, by using BC fractions equal to 0 (soil only), 0.014, 0.091, 0.23, 0.33 and 1 (BC only). The results indicated that BC significantly (p = 0.05) increased soil porosity and the amount of storage pores. As a consequence, water retention was enhanced and AWmax from 19.3 mm/m for the sandy soil (fbc = 0), to 60.8, 102.3 and 107.6 at fbc = 0.091, 0.23, and 0.33, respectively, was raised. No significant effects of BC were detected on the soil water retention curve of the BC-amended soil at fbc = 0.014, compared to the original condition. The significant increase in the structural index (SI) at fbc, ≥0.091, indicated that BC improved soil aggregate stability. The BET-SSA was measured by nitrogen adsorption measurements and indicated that the connected porosity was significantly increased by the 0.091 BC fraction. Both AWmax and SI were found to be correlated with BET-SSA. This showed an outcome that has been so far little investigated, namely that the BET-SSA played a significant role in the mechanism affecting the soil response to BC addition. The results showed that application of BC can improve soil structure and water retention and therefore optimize irrigation management by reducing irrigation needs, in the Al-Foah area and/or in similar dryland regions.

This paper aimed at investigating if the application of biochar (BC) to desert sand (DS) from the United Arab Emirates (UAE), characterized by a very poor soil-water retention (SWR) and by a very low value of the maximum water available for crops (AWmax), could positively affect soil water balance, by reducing the irrigation needs (VIRR) and improving the irrigation water use efficiency (IWUE) and the water use efficiency (WUE). The analysis was performed for three crops, i.e., wheat (Triticum aestivum), sorghum (Sorghum vulgare) and tomato (Lycopersicon esculentum). BC was applied to the DS at different fractions, fBC (fBC = 0, 0.091, 0.23 and 0.33). Drip irrigation was adopted as a highly efficient water saving method, which is particularly relevant in arid, water-scarce countries. Soil water balance and irrigation scheduling were simulated by application of the AQUACROP model, using as input the SWR measured without and with BC addition. The effect of BC was investigated under either a no-water stress (NWS) condition for the crops or deficit irrigation (DI). The results showed that the application of BC made it possible to reduce the predicted VIRR and to increase the IWUE under the NWS scenario, especially for wheat and sorghum, with less evident benefits for tomato. When a deficit irrigation (DI) was considered, even at the lowest considered fBC (0.091), BC counterbalanced the lower VIRR provided under DI, thus mitigating the yield reduction due to water stress, and improved the WUE. The influence of BC was more pronounced in wheat and tomato than in sorghum. The results evidenced that the application of BC could be a potential strategy for saving irrigation water and/or reducing the effects of drought stress in desert sand. This means that biochar could be used a management option to promote local production and reduce the dependency on food import, not only in the UAE, but also in other countries with extremely arid climatic conditions and large extensions of sandy soils similar to the considered DS.

The aim of the present study was to investigate structure alterations of a sandy-clay soil upon addition of different amounts of biochar (f bc ). All the f bc samples were analyzed by high energy moisture characteristic (HEMC) technique and 1H nuclear magnetic resonance (NMR) relaxometry. HEMC was applied in order to evaluate aggregate stability of biochar-amended soil samples. 1H NMR relaxometry experiments were conducted for the evaluation of the pore distributions through the investigation of water dynamics of the same samples. The HEMC technique revealed improvement in aggregate stability through measurements of the amount of drainable pores and the stability ratio. The latter increased as the amount of biochar was raised up. The 1H NMR relaxometry revealed a unimodal T 1 distribution for both the sole sandy-clay soil and the biochar. Conversely, a bimodal T 1 distribution was acquired for all the different f bc samples. Improvement in aggregate stability was obtained as biochar was progressively added to the sandy-clay soil. A dual mechanism of water retention has been hypothesized. In particular, intra-aggregate porosity was indicated as the main responsible for molecular water diffusion when f bc comprised between 0 and 0.33. Conversely, inter-aggregate porosity resulted predominant, through swelling processes, when f bc overcame 0.33.

Management scenarios aimed at optimizing irrigation in a Sicilian vineyard characterized by a cracking clay soil irrigated with saline water were explored for seven soil profiles (Baglio 1-Baglio 7), by using the simulation model soil-water-atmosphere-plant environment (SWAP), which accounts for shrinkage and cracking. Accurate prediction of water content, 0, was obtained for the seven profiles by expressing the soil hydraulic properties according to the Brutsaert retention equation coupled with the hydraulic conductivity model proposed by Gardner (B-G model). A satisfactory prediction of the electrical conductivity of saturated extract (EC sat ) was obtained using for the dispersivity (L dis ), a calibration value of 20 cm. Different irrigation schedulings and alternating waters of different quality were then explored as viable management options. The results showed that bypass flow determined a favorable water distribution, and that the best irrigation strategy was to make a minimum number of irrigations, by maximizing at the same time the amount of water supplied at each irrigation. Water storage in cracks was found to promote salt-leaching; neglecting cracks and bypass flow was shown to overestimate salinization. Alternating two different irrigation waters proved to be the best strategy, which could be adopted to reduce soil salinization and enhance crop transpiration. Findings concerning the role of cracks in the process of salt-leaching suggested that, under field conditions, application of a leaching solution was more efficient if the soil presented a considerable degree of cracking.

In Sicily, the increasing scarcity of good-quality waters is spreading irrigation with saline–sodic waters, thus enhancing the risk of soil secondary salinization and sodication. Sustainable management strategies are urgently needed in Sicily to prevent extent of salinization and sodication, thus preserving soil quality. Since irrigation is performed in cracking soils using irrigation systems involving high application rates, bypass flow of water and solutes occurs during irrigation. The objectives of this paper were (i) to investigate the process of Na–Ca exchange and subsequent salinization/sodication during bypass flow and (ii) to explore possibilities of using cyclic strategies, based on alternating good-quality waters to saline solutions, to prevent salinization. Six NaCl–CaCl 2 solutions (named 1–6) with the following values of sodium adsorption ratio (SAR, [mmol c /l] 0.5 ) and of cationic concentration ( C , mmol c /l)—(1) SAR=5, C =20; (2) SAR=5, C =1; (3) SAR=15, C =25; (4) SAR=15, C =2; (5) SAR=30, C =30; and (6) SAR=30, C =5—were prepared in laboratory. Two undisturbed soil columns were sampled in a Sicilian irrigated area where a risk of secondary salinization and sodication was indicated by previous investigations. Bypass flow experiments were performed by supplying the six solutions to each soil column in the order from 1 to 6 at an almost constant initial value of the cracking volume, using an application intensity determining occurrence of bypass flow. Results of experiments showed that in concomitance with bypass flow, (1) a process of Na–Ca exchange occurred, with Na adsorption and accumulation in the soil. In both the two columns, the exchangeable sodium percentage (ESP) was found to increase by about 100% at the end of the six bypass flow experiments. Being the volume of the supplied saline/sodic solutions much smaller than the pore volume, this result indicates that a considerable risk of sodication may occur under bypass flow conditions; (2) cyclic strategies are useful for preventing accumulation of solutes when solutions with SAR close to the soil ESP are used. Instead, when solutions with SAR higher than the initial ESP are supplied to the same soil, due to the Na–Ca exchange and subsequent sodication, alternating waters having not only lower C but also lower SAR could be necessary to prevent salinization and sodication.

The relevance of bypass flow on water flow, solute or pesticide transport is becoming increasingly recognized. Recent investigations proved that soil salinization may be influenced by bypass flow, i.e. the rapid transport of water and solutes via macropores and/or shrinkage cracks to subsoil and groundwater. This paper explores the role of bypass flow in the process of accumulation and leaching of solutes, as well as of sodium, in a Mediterranean cracking soil irrigated with saline/sodic waters. The results of bypass flow experiments performed on undisturbed soil cores showed that leaching of solutes occurred in concomitance with bypass fluxes when a low salinity solution was alternated with a high salinity solution. Exchange of solutes between the incoming solution and the soil matrix occurred during the bypass flow events at the contact surfaces (cracks walls) between the solution and the soil matrix and where cracks terminated in the soil samples. Concomitant exchanges of sodium were indicated by measurements performed in the effluent solution during the bypass flow measurements. The amount of Sodium released from the soil during the bypass flow events, as well as that of the soluble salts leached from the soil, were found to depend on the degree of soil cracking. These results indicated that: 1 in management of irrigation in cracking soils, under the occurrence of bypass fluxes, alternating a low salinity/sodicity water with a high salinity/sodicity solution can be effective for preventing salinization and sodification: 2 greater efficiency of removal of sodium/soluble salts can be obtained if application of the leaching solution is performed when the soil is at a considerable degree of cracking.

Laboratory determination of soil hydraulic characteristics (HC) is performed on cylindrical confined soil cores, while resin-coated small natural aggregates are prevalent for determining the Soil Shrinkage Characteristic Curve (SSCC). Because of the different geometry and volume of clods and cores, incorporation of shrinkage in HC of clay soils could be affected by the use of SSCC determined on natural aggregates or on confined cores. The objectives of this study were (i) to investigate differences between the SSCC obtained on resin-coated natural aggregates (volume V = 20-30 cm 3 ) and on cylindrical confined cores having a volume (650 cm 3 ) close to that of cores used for HC laboratory determination, (ii) to test the performance of different models proposed for analytical interpretation of the SSCC, and (iii) to derive regression equations predicting the SSCC from routinely measured soil physical properties. Using twenty-one Sicilian soils of variable shrink-swell behavior, we found significantly larger specific volume (n ), indicating less shrinkage, in the cylindrical confined cores. The investigation also proved the good fitting of a two-line model to the measured SSCC and the possibility to predict the basic shrinkage line from the clay content. These results suggest that incorporation of shrinkage in HC of clay soils should be based on the SSCC measured or predicted on cores with geometry and dimensions as those used for routine laboratory measurement of HC.

This chapter presents results of a 3-year field investigation in a vineyard located in Sicily (Mazara del Vallo, Trapani) within the framework of the Project “Evolution of cropping systems as affected by climate change” (CLIMESCO). Soil-plant responses to two saline irrigation waters were determined by measuring soil hydrological characteristics, soil salinity, crop transpiration and stomatal conductance in field plots of a Sicilian vineyard. The results proved that crop transpiration (T r) and stomatal conductance (G s) were significantly affected by soil salinity conditions, expressed by electrical conductivity of soil saturation extract (ECe). Significant reductions in T r and G s were found in plants irrigated with water of ECw = 1.6 dS m−1 (L) compared to T r and G s values in plots irrigated with water ECw = 0.6 dS m−1 (R). Significantly higher crop water stress index (CWSI) values, indicating stronger stress conditions, were measured in the L treatment, relative to the R treatment. Validity of the linear relationship between relative yield and relative transpiration was confirmed. A value of 0.7 for the yield response factor (Ky) provided accurate prediction of yield reduction in years 2008 and 2009. Reductions due to soil salinity, calculated according to Maas and Hoffman equation, showed that under conditions of water and salinity stress, yield reduction due to salinity represented a percentage of the total yield reduction of up to 11% in the L plots and up to 3.5% in the R plots. The investigation also indicated that ECe (1.5 dS m−1) discriminated a different plant response to salinity, indirectly confirming the Maas threshold value for grapes. Under the irrigation conditions in the Sicilian vineyard, it is suggested to implement management strategies aimed at keeping soil salinity below this threshold value. This can be realized by using low-salinity irrigation water only or by alternating the two irrigation sources.

An exchangeable sodium percentage (ESP) >15 is traditionally considered to affect soil structural and hydraulic characteristics. Recent investigations show that both this critical value and the concept of critical threshold need reconsideration, because soil degradation often takes place even at lower ESP in dilute solutions, and soil behavior at increasing ESP appears to be a continuum. This study was carried out to analyze the response of two Sicilian Typic Haploxererts to ESP values up to 15, at a low cationic concentration. The investigation was carried out on aggregate stability, rating of soil shrink-swell potential, and both saturated and unsaturated hydraulic conductivity. The specific purpose was to verify if a critical ESP threshold exists, or if the hypothesis of a continuum behavior is more appropriate. The high-energy moisture characteristic technique was used for determining aggregate stability, and Brasher's method for the shrinkage characteristic. The constant-head method was used for determining saturated hydraulic conductivity, and the parameter estimation method based on one-step outflow experiments for unsaturated hydraulic conductivity. Almost linear relationships were found between the investigated soil properties and ESP, indicating no critical ESP threshold; furthermore, the results obtained indicate that an effective hazard of soil quality degradation can be forecast even in a 2 to 5 ESP range at a low cationic concentration. This is a basic indication for irrigation management aimed to combat and prevent degradation of soil quality.

Water demand is increasing worldwide. In regions affected by water scarcity such as those located in the Mediterranean basin, water supplies are already degraded, or subjected to degradation processes, which worsen the water shortage. In Sicily, the increasing scarcity of good quality water is expanding irrigation with saline-sodic waters, thus enhancing the risk of secondary salinization and sodification. Adequate management practices are urgently needed for sustainable use of saline/sodic waters. This chapter illustrates how the Geonics EM-38 probe was used for monitoring salinization in a Sicilian area where irrigation with saline water is increasingly practiced, and the risk of salinisation and desertification is envisaged. Electrical conductivity of bulk soil (ECa) measurement grids were taken with the EM-38 in a Sicilian vineyard at several dates, both prior to, and following irrigations, with two distinct irrigation treatments of different salinities (0.6 and 1.6 dS m–1 respectively). Though both water sources contributed to field salinity, high salinity source had a more adverse effect. This investigation proved the usefulness of EM-38 for efficient, rapid monitoring of the progressive effects of different irrigation strategies on soil salinization.

Water demand is increasing worldwide. In regions affected by water scarcity such as those located in the Mediterranean basin, water supplies are already degraded, or subjected to degradation processes, which worsen the shortage of water. In such regions, competition for scarce water resources among users will inevitably reduce the supplies of freshwater available for crop irrigation. Detailed studies and experimental projects are needed to develop management scenarios aimed at preventing desertification and conflicts for use of the increasingly limited water resources and cultivable land. This paper illustrates soil-plant responses to irrigation with saline water in a Sicilian vineyard located in a wine production area (Mazara del Vallo, Trapani, TP). Two irrigation treatments of different salinities, R and L, having electrical conductivities of 0.6 and 1.6 dS m, respectively, were applied at several dates, using a drip system, in a silty-clay soil. Soil measurements were taken to monitor water content (θ) and EC of saturated extract (ECsat). Plant responses to water and salinity conditions were explored by measuring crop transpiration (T) and stomatal conductance (Gs) at several dates during the irrigated season. Results showed that significantly lower T and Gs values were measured in field sites with lowest and highest ECsat.

In this paper morphological and physical characteristics, as well as flow behaviour of a Mediterranean Vertisol under the influence of two different irrigation systems currently used for irrigation, i.e. drip and sprinkler systems, were compared. No differences in soil texture, compaction and in potential cracking were found on cores from the two fields. However, field application of methylene blue showed the presence of continuous macropores, penetrating up to depths of 20-25 cm from the soil surface, in the field where the drip system was in use (field 1). This was considered to be the pre-existing soil structure. Instead, macropores terminating at a depth ranging between 5 and 10 cm from the soil surface were observed in the sprinkler irrigated field (field 2). The same difference in terms of macropores' continuity was also observed on soil cores sampled from the two irrigated fields. The higher raindrop impact and the non-point water application involved in the sprinkler irrigation system were assumed to have determined, during several years, the different depth of penetration of the macropores in the two fields. A different hydraulic behaviour was evidenced by laboratory measurement of bypass flow on soil cores taken from the two fields. Specifically, higher values of the saturated hydraulic conductivity were found in the cores from the drip irrigated field compared to those sampled in the sprinkler field. In addition no bypass flow was measured in the columns under the sprinkler field, while high rates and amounts of bypass flow were obtained in the cores taken from the drip irrigated field. The different hydraulic behaviour observed in the cores taken from the drip and from the sprinkler irrigated field was in agreement with the difference in terms of macropores' continuity between the two fields. Being bypass flow a mechanism inducing leaching of solutes, results of this investigation suggest that irrigation systems affecting soil structure, and altering macropores' continuity, should be avoided in clay soils. (c) 2006 Published by Elsevier B.V

In Sicily, the increasing scarcity of quality water is leading to irriga- from salinization (Crescimanno et al., 2004). tion with saline water in soils having a considerable susceptibility to In Sicily, the increasing scarcity of good quality water cracking. Irrigation systems involving high application rates are used coupled with intensive use of soil under semiarid to arid in these irrigated areas, and bypass flow during irrigation is thus climatic conditions, is leading to irrigation with saline prevalent. Adoption of management practices accounting for cracking water on soils having a high shrink-swell potential and is therefore necessary to prevent salinization and land degradation. susceptibility to cracking (Crescimanno and Provenzano, In this paper, water flow and solute transport in a Sicilian cracking 1999). These soils are irrigated in the summer season, soil irrigated with saline water was simulated by using the soil-water- when the cracks open up, by sprinkler systems, which inatmosphere- plant environment (SWAP) model, and the simulated volve high application rates. Because of these high apresults compared with measured values of soil moisture and salinity. plication rates, bypass flow, that is, the rapid transport The soil hydraulic parameters were obtained by inverse method based of water and solutes via macropores or cracks to subsoil on multi-step outflow experiments, adopting two different sets of hy- or to groundwater (Bouma, 1991; Crescimanno, 2001), draulic parameters/functions, that is, (i) the van Genuchten-Mualem, (VGM model) and (ii) the Brutsaert retention equation coupled with is prevalent during irrigation. the hydraulic conductivity model proposed by Gardner (B-G model). Laboratory investigations performed on undisturbed The results obtained using field measurements from four soil profiles soil columns sampled from these areas showed that saliof a cracking clay soil showed that SWAP provided accurate predic- nization or leaching occurred during bypass flow dependtions of water content, , when the soil hydraulic properties were ing on the concentration of the applied solution compared expressed according to the B-G model. Using the B-G hydraulic pa- with the concentration of the pore solution (Crescimanno rameters/functions, the model was calibrated with reference to the and De Santis, 2004); the efficiency of salt-leaching was dispersivity (Ldis).Acalibration value of about 20 cm was found for the found to depend on crack volume (Crescimanno et al., four different profiles. In the conditions occurring in the Sicilian area 2002). The low values of the sodium adsorption ratio where we are focusing our attention, the predictive errors associated (SAR) of irrigation water, and the low values of the exwith the simulated ECsat, can be considered acceptable if the purpose changeable sodium percentage (ESP) measured in these of application is to predict the influence of salinity on crop yield.