Soil salinization risk assessment owing to poor water quality drip

Salinization causes soil degradation and soil fertility reduction. The main reasons for 11 soil salinization are poor irrigation water quality and incorrect irrigation management. 12 Soil salinization is accelerated owing to irrigation with treated wastewater with 13 elevated salt concentration. The study area is located in the Beit She'an Valley, one of 14 the most important agricultural regions in Israel. The combination of soil salinization 15 and poor drainage conditions impedes plant development and is manifested in 16 economic damage to crops. Without clear irrigation criteria, an increase in soil salinity 17 and steady damage to soil fertility might occur. The study objective was to provide an 18 assessment of soil salting processes as a result of low-quality irrigation water at the 19 Kibbutz Meirav olive plantation. This study combined various research methods, 20 including soil salinity monitoring, field experiments, remote sensing (FDEM), and 21 unsaturated soil profile saline water movement modeling. The assessment included the 22 salinization processes of chalky soil under drip irrigation by water with various 23 qualities. With a drip irrigation regime of water with a dissolved salt content of 3.13 24 dS/m, the salinization process is characterized by salts accumulation in the upper root 25 zone of the trees. The modeling results showed that there is a soil salinization danger 26 in using brackish water and that irrigation with potable water helps to reduce soil 27 salinization. 28 29


34
Soil salinity surveys and studies across the world and, in particular, in Israel indicate 35 that irrigation with poor water quality and improper irrigation management causes soil 36 salinization and degradation, and also damages soil fertility (Wada et al., 2016;Pandit 37 et al., 2020). Soil salinity monitoring in the Jezre'el Valley began in 1987, following a 38 soil salinity survey that showed intensive salinization and often alkalinization of the 39 upper soil horizons (Benjaminy et al., 2005(Benjaminy et al., , 1998(Benjaminy et al., , 2000. Earlier studies (Gafni et al.,40 1990) had shown that these processes were enhanced by a semi-confined shallow 41 aquifer (Kruseman and De Ridder, 1976), causing upward water flow during winter 42 and spring seasons and reducing downward rain and irrigation percolation during the 43 summer and fall seasons. 44 Most of the soil salinization problems in the Beit She'an Valley are affiliated with the 45 use of poor-quality irrigation water. The soil salinity is constantly increasing, owing to 46 irrigation with high salinity-treated wastewater and blocking of the natural drainage to 47 (Celia et al., 1990;Bear, 1972) and root water uptake is calculated by the van 65 Genuchten equation (van Genuchten, 1987). In such models, the soil hydraulic 66 conductivity coefficient in the saturated media varies as a function of the soil's 67 hydraulic conductivity. 68 Soil moisture may be evaluated through atmospheric conditions (Garrigues et al.,69 2015), or calculated as a function of suction (pressure head) and hydraulic 70 conductivity in an unsaturated condition. Salt leaching and accumulation is significant 71 is arie and semi-arid areas (Wada et al., 2016). Models of salt motion are commonly 72 based on the Fickian convection-dispersion equation for solute transport (Toride et al.,73 1993) and complex models should also consider absorption processes, anion and 74 cation exchange, and more. Several modeling platforms such as "HYDRUS" 75 (Simunek et al., 1998) and "WASTRC-1" (Mirlas et al., 2006) are widely used. The 76 WASTRC-1, one-dimensional water and solute movement model of under saturated 77 conditions, was found to fit the soil characteristics of Hula Valley irrigated fields in 78 Israel. In both "HYDRUS" and "WASTRC-1" models, various soil hydraulic 79 conditions such as drainage, irrigation, layer saturation depth can be considered. Soil 80 density, saturated hydraulic conductivity, field moisture, suction, and root zone 81 development among other factors are prerequisites for model calibration, parameter 82 validation, and, consequently, proper water and solute movement simulation 83 (Garrigues et al., 2015). 84 Salinization during irrigation is a dynamic process as the number of salts in the soil 85 and their composition change during irrigation both in the area and in the soil profile. 86 Soil salinity mapping by the traditional sampling method is expensive and time-87 consuming, with mapping accuracy directly depending on the distance between the 88 sampling points. Remote sensing technologies that are based on active electromagnetic 89 (EM) radiation are being widely adopted for soil salinity mapping. Ground-based EM 90 methods measure electrical conductivity (EC) in subsurface and substratum horizons 91 and can thus recognize salinity anomalies in the field before salinization approaches 92 the surface (Farifteh et al., 2007). EM induction sensors measure the soil profile 93 salinity by recording the soil's apparent electrical conductivity (ECa).  (Ben Dor et al., 2009b).

100
The soils of the Beit She'an Valley were selected for research as it is one of the most 101 important agricultural areas in Israel. They consist of brown clay soils (grumusols) and 102 chalky soils, with the latter's profile characterized by thin layers and formation layers 103 of marl with high water absorption capacity. The soil stratification influences the 104 potential to drain and wash excess salts that accumulate during the irrigation season, 105 which preserve ventilated root conditions. Sodium rich soil has up to 30% cation 106 exchangeable capacity, which exacerbates the ventilation conditions necessary for 107 plants. The combination of soil stratification and poor drainage conditions impedes 108 plant development and, in some cases, the soil structure destruction and salts 109 accumulation in the root zone causes plant degeneration due to water absorption 110 difficulties (Machado and Serralheiro, 2017). As a consequence, crop irrigation by 111 brackish water in the Beit She'an area might cause economic damage.

112
The irrigation water sources in the area are of variable quality: springs and Jordan 113 River water are considered of acceptable quality, while groundwater and also effluent 114 water might be of poor quality. In this latter case, low irrigation water quality without 115 clear irrigation criteria might steadily damage soil fertility. Defining an irrigation 116 regime for local soil and water quality conditions is, therefore, of great importance for 117 preventing crop and economic damage in the Beit She'an Valley. This knowledge can 118 indicate how water and salt move in soil and correlate to salinity processes and 119 irrigation management capability. Combining remote sensing (FDEM) methods with 120 water and salt movement models in the unsaturated soil layer may enable effective 121 identification of soil salting processes. In turn, this may result in improved planning 122 and control of irrigation systems. 123 https://doi.org/10.5194/gmd-2020-231 Preprint. Discussion started: 6 August 2020 c Author(s) 2020. CC BY 4.0 License.

5
As an integrative knowledge harvesting demonstration needed for irrigation 124 management, this study's objective was to assess soil salting processes as a result of 125 low-quality irrigation at the Kibbutz Meirav olive plantation in the Beit She'an Valley. The Beit She'an area is a unique agricultural area due to a combination of warm and 131 dry climate (annual evaporation of 2400 mm at the meteorological service, Eden Farm 132 Station), saline water irrigation, and heavy soils. The study site is Kibbutz Meirav, a 133 mature (2002) olive plantation located 1100 m north of the Kibbutz (Fig.1.).  The main irrigation water sources in the area are Jordan River water and local 154 groundwater whose salinity and SAR ratio are very high, mainly due to high sodium 155 chloride concentrations. The chloride concentration is at a range of 800 -1700 mg/l 156 and electrical conductivity is above 3.5 dS/m. Local authorities intend to dilute the 157 local water by effluent water and reduce the chloride concentration in water to 800 158 mg/l.

159
The Kibbutz Meirav olive plantation irrigation water quality test results for different 160 seasons during the study period are presented in Table 1.  conditions (Corwin and Lesch, 2005). The suction and soil moisture monitoring during   The water and salt movement, a basic mathematical model of one-dimensional 263 equations for an unsaturated soil state, was: 264 (2) 266 ( 3)  267 where: The hydraulic model used was the van Genuchten-Mualem (no hysteresis) single 278 porosity model (van Genuchten, 1980). As a soil salinization model,  was used as a time weighting scheme (Crank and Nicolson, 1947) and the Galerkin 280 Finite Scheme (Fletcher, 1983) for a space weighting scheme equilibrium model. For

351
The amount of general chalk in the soil was very high and hardly changed during the 352 study period. The amount of general chalk ranged from 70% to 85% and did not 353 depend on soil moisture and irrigation regime.

357
The soil suction that was measured in-situ using the first tensiometer station is shown 358 in Figure 8. In station 1, the soil suction before irrigation varied from 140 to 300 mbar  distribution. Active chalk values ranged from 15-20% to 30-33%, with higher 384 concentration at a depth of 20-60 cm, which did not change during the experiment.

385
Weighted soil moisture ranged from 0.14 to 0.36, which increased with depth. best fit between model calculation and soil mechanical composition field 435 measurements was obtained for the silty clay type soil (Fig. 2). The volumetric 436 moisture model calibration was similar to the calculated results (Fig. 13). The  (Table 2).  .6). Irrigation by potable water (Fig.16   The one-dimensional model created for water and movement of dissolved salts showed 543 the danger of using brackish water for irrigation. Since soil salinization exceeds an 544 acceptable level for trees, the use of potable water for irrigation, if possible, will help 545 to reduce soil salinization.