افروز تقی زاده قصاب

Determination of agricultural water consumption, as the main consumer of the country's water resources, is very important in order to plan and manage resource consumption and establish food security, water security and improve the livelihood of the growing population. Water consumption or actual evapotranspiration is the part of water used or delivered to the agricultural sector that is out of reach and cannot be reused. Estimating the spatial distribution of actual evapotranspiration (ETa) based on valid satellite data is a new approach in planning and determining water balance. In the study, amounts of actual evaporation, transpiration and evapotranspiration in the country and agricultural, horticultural and rainfed land uses were extracted using the methodology introduced by Food and Agriculture Organization (FAO), which is presented in the WaPOR database. The results showed that the highest actual evapotranspiration about 2500 mm occurs on the north coast and Lake Urmia. The results showed that the average amount of actual evapotranspiration in irrigated horticultural lands was 299.30 mm and in irrigated agricultural lands was 301.52 mm in a 12-year period. Accordingly, the amount of actual evapotranspiration of irrigated lands on a national scale and for the year 2018-2019 was calculated to 28.84 billion cubic meters, which is equal to 20.78 and 8.06 billion cubic meters for agriculture and horticulture, respectively. Furthermore, 72.1% of that belongs to transpiration and the other of that 27.9% belongs to evaporation.

Sugar beet is one of the main products with high water requirement in Urmia Lake basin. Planting spacing and irrigation method of sugar beet has an important impact on increasing irrigation efficiency, crop yield and physical water productivity of this crop. In order to investigate the effect of planting spacing on irrigation efficiency, physical water productivity and crop yield, a field study was conducted on two pilot farms (A and B) in Miandoab irrigation network under farmer’s management during 2017. In this study a part of each farm was considered as control (common planting spacing and border irrigation) and the other part was considered as treatment (change the planting spacing and surface irrigation method from border to furrow irrigation). The control part of the farm included a low height groove inside the border and at 50 cm intervals (IA-C and IB-C) and the treatment part of each farm included two-row crop planting of sugar beet (so-called 40×60 cm: IIA-T and IIB-T) and furrow irrigation. According to the results, the maximum water application efficiency was obtained about 77.2% in IIA-T and the lowest efficiency was obtained about 10.2% in IB-C. The average irrigation efficiency (in 12 irrigation) in IIA-T and IIB-T were 54.5% and 51.1%, respectively and in IA-C and IB-C were 38.7% and 39.3%, respectively. Based on the results, by changing the planting pattern from common spacing to two-row (40×60) and irrigation method from border to furrow, the average water consumption reduced about 29.7% and the average yield increase from 64.3 to 74 ton/ha (increase by 15.2%). Also, the average physical productivity of sugar beet increased from 3.75 to 6.47 kg/m3 (increase of 2.71 kg/m3).

A challenge of sustainable development is related to agriculture, food security, and conservation of water and soil resource, under the current crop production paradigm. Increasing crop yields often have negative environmental impacts. Soil salinization and sodication are major environmental hazards that limit agricultural potential and are closely related to agricultural unsuitable management and water resources overexploitation, especially in arid climates. In this study, we investigated the negative impacts of saline and sodic irrigation water on soil properties that it is necessary to study the factors affecting the degradation of soil structure to implement proper land management and we intended to help the farm producer or landowner to understand the fundamental differences between these two problems. Samples of clay loam and sandy loam soils were treated in 5 wetting and drying periods with different types of water quality (which combinate different levels of EC and SAR). Soil water content of samples was achieved at soil matric suctions of 0, 10, 20, 40, 60, 100, 300, 1000, 2000, 4000 and 15000 cm. Also, dispersible clay and saturated hydraulic conductivity were determined. Results showed that increasing of SAR caused dispersion of clay and saturated hydraulic conductivity was decreased with increasing of dispersed clay. Increasing SAR caused some macropores and mesopores changed to micropores and as result enhanced water retention especially at high matric suctions. Water retention capacity was enhanced by increasing in water EC as that flocculated soil particles and created new soil pores.

The effect of water quality on soil water retention, structure, and hydraulic conductivity in two soil textures was studied. Undisturbed soil samples were treated in 5 wetting and drying periods with 6 different types of water quality consisting of 2 levels of EC (0.2 and 10 dS m-1) and three levels of SAR (1, 5 and 12). Undisturbed soil samples were equilibrated on sand box apparatus to soil matric suctions of 0, 10, 20, 40 and 60 cm and on pressure plate apparatus to soil matric suctions of 100, 300, 1000, 2000, 4000 and 15000 cm. The van Genuchten-Mualem model was fitted to simulate the measured soil water characteristic curve. Soil physical quality index (S) and the inflection point of water retention curve (θINFL) were evaluated using fitted parameters. Also, the macro-porosity, meso-porosity, micro-porosity, available water content (AWC100 and AWC300), and saturated hydraulic conductivity were measured. The study was conducted in a completely randomized design with three replications. Results showed that increasing EC caused soil particles flocculation, by developing some new pores and, consequently, increasing water retention capacity. Although increase in SAR dispersed soil particles, alteration of some macro-pores and meso-pores to micro-pores enhanced water retention, especially at high matric suctions. But, the available water content did not change significantly. Also, increase in water EC enhanced water retention at all matric suctions and the highest moisture content at inflection point was seen at EC of 10 dSm-1. The increase in SAR and decrease in EC were directly related to decrease in saturated hydraulic conductivity. Soil physical quality index (S) decreased by sodium increment, which indicated the reduced soil physical quality.

In many arid and semi-arid countries, population growth and the need for increased food production are forcing the management planners to consider all sources of water to achieve further development. Water quality could affect soil physical, chemical, and biological properties. A laboratory experiment was carried out to study the effect of soil texture and salinity and sodicity of water on some physical and mechanical properties of the soil. Two soils with sandy loam and clay loam textures were treated with twelve waters with different qualities, i.e. combinations of four levels of salinity (EC) including 0.2, 1, 6, and 10 dS m-1 and three levels of sodicity (SARs of 1, 5, and 12), and were subjected to wetting and drying for five times. The consistency limits, plastic and friability indices, dispersible clay and optimum water content in Proctor compaction test were determined. The significant effects of treatments on the determined soil properties suggested that water quality altered the soil microstructure. Effects of salinity and sodicity on clay loam soil were more than sandy loam soil. Unlike the clay loam soil, in the sandy loam soil, the consistency limits did not significantly change as a result of low clay content. At each salinity treatment, the higher the SAR of water, the greater was the impact on soil microstructure; as the plasticity index was increased and friability index was decreased, both might result in undesirable tillage operations. Increase in the calcium concentration at each SAR treatment reduced the dispersible clay and increased Proctor test optimum water content.