IRRIGATION_2 Design of Irrigation Systems by László Ormos

Soil properties nt Silty clay ilt ts rce en pe Clay loam rc cla y Clay pe Soil texture(water holding capacity) • Clay <0. 002 mm • Silt 0. 002 -0. 02 mm • Fine sand 0. 02 -0. 2 mm • Coarse sand 0. 2 -2 mm • Gravel >2 mm Sandy clay Silty clay loam Sand Loamy sand percent sand Sandy loam Loam Soil texture Silt loam Silt

Soil properties Soil structure (infiltration rate) Single grains Infiltration rate rapid (20 -100 mm/hr) Prismatic Platy Infiltration rate moderate Infiltration rate slow (4 -5 mm/hr)

Soil-water-plant relationship Soil moisture Total water potential acting is as following: where Pt is the total water potential, Pm is matric potential due to capillary forces, • adhesion force (attractive force betweenthe solid particle and the water) • cohesion force (attraction between water molecules) Pg is gravitational potential due to the gravity, Po is osmotic potential due to the dissolved salts in the water, Pp is pressure potential due to the position with respect to a fixed datum level.

Soil-water-plant relationship Classes and availabilities of soil water Saturation Field capacity Available moisture Gravitational water Rapid drainage Capillary water Slow drainage Permanent wilting Unavailable moisture Hygroscopic water Essentially no drainage

Soil-water-plant relationship Suction Hysteresis effect Moisture content

Soil-water-plant relationship The movement of water in the soil • Hydraulic conductivity (or flow velocity) where Q is the amount of water which moves through the soil, A is the cross section area of the tested soil sample, H is the difference in water pressure head between two points, L is the distance between the two points, KS is the Darcy coefficient of proportionality.

Soil-water-plant relationship KS in saturated soil is the following: Kn. S in unsaturated soil is the following: where h. G is the hydraulic gradient computed as follows: H 1 and H 2 are pressure head values.

Soil-water-plant relationship Infiltration under various methods of irrigation • Furrow irrigation: gravitational influence, • Flood irrigation: gravitational influence, • Sprinkler irrigation: water distribution is more or less symmetrical, • Micro-sprinkler: the distribution pattern is trapezoid, and wets the area only partially (50 -70%), • Drip irrigation: cone-shaped volume of moistured soil surrounding the plant root-zone, size and shape depend on the type of soil, the discharge of dripper, and the duration of water application.

Soil-water-plant relationship Root distribution in the various soil layers 40% 30% 20% 10% Soil depth [cm] 0 3 D/4 D/4 Root zone extraction Depth D Water distribution in the soil 10 7. 4% 68. 7% 10. 3% 20 9. 4% 30 4. 2% 40

Soil-water-plant relationship Storage in soil • Small pores are required to store the water. • Medium-sized pores help the movement of water in the soil. • Large-sized pores are required for aeration of soil. The saturation • Saturation capacity means the pores of soil are full filled with water. • Gravity occurs the water drains quickly from the root zone.

Soil-water-plant relationship Field capacity Fc • • The moisture content of soil means the remained water quantity after the gravitational water has been removed. Field capacity depends on the texture of soil. Permanent wilting point Pw • • • It is the minimum of the available moisture of soil. When water content is at the wilting point or it is lower then plants permanently wilt and they might not be recovered after being placed in moisturized environment. Wilting point is influenced by soil texture. Temporary wilting point • It is occurred in any hot windy days but plants will recover in cooler portion of days.

Soil-water-plant relationship Available soil water AW where AW is in percent of moisture volume, S is the specific density of soil and W is the specific water density. The depth of available soil water for a 1 m layer AWDm

Soil-water-plant relationship The depth of available water in the soil layer of depth Z AWDZ where Z means the soil layer of depth. The available water volume in the soil layer of depth Z AWVZ

Soil-water-plant relationship The depth of available water in the main root zone Zr of the crop AWDZr where Zr is the depth of main root zone. After replacement in this equation, calculation directly the depth of available water in the main root zone is as follows:

Soil-water-plant relationship The available water volume in the main root zone Zr of the crop in a hectare AWZr The net water application NWA where PWD is the permitted water deficit. The available net water application in the main root zone Zr of the crop in a hectare AWZr

Soil-water-plant relationship The gross water application GWA where irr is the efficiency of irrigation. The irrigation interval Ir. I where CU may be either the consumptive use, or evapotranspiration.

Soil-water-plant relationship Calculate the available water volume per hectare in a soil with a homogeneous profile according to the following data: • • • Field capacity Wilting point Soil density Water density Main root zone Fc=17[%] Pw=7 [%] S=1. 3[g/cm 3] W=1. 0[g/cm 3] Zr=0. 4[m]

Soil-water-plant relationship 1. Available water by volume: 2. The depth of available water for a 1 m layer: 3. The depth of available water in the effective root zone Zr:

Soil-water-plant relationship 4. The available water in a hectare, in the effective root zone Zr:

Soil-water-plant relationship Calculate the available water volume per hectare in a soil with different texture layer according to the following data: Layer Fc Pw S [%w] [g/cm 3] Sandyloam 13 5 1. 5 0. 15 loam 20 8 1. 4 35 -65 0. 30 Clayloam 27 13 1. 4 65 -110 0. 45 clay 32 16 1. 3 Layer Depth Layer thickness [cm] [m] 1 0 -20 0. 2 2 20 -35 3 4 Soil texture

Soil-water-plant relationship The applied equation is Fc-Pw [%] S [g/cm 3] Zr [m] AWDZr [mm/layer] 13 -5 1. 5 0. 2 24. 0 20 -8 1. 4 0. 15 25. 2 27 -13 1. 4 0. 3 58. 8 32 -16 1. 3 0. 1 20. 8 AWDZr (Zr=0. 75 m) 128. 8

References Azenkot, A. (1998): ”Design Irrigation System”. Ministry of Agriculture Extension Service (Irrigation Field service), MASHAV Israel Dr. Avidan, A. (1995): ”Soil-Water-Plant Relationship”. Ministry of Agriculture Extension Service (Irrigation Field service), CINADCO, Ministry of Foreign Affairs, MASHAV, Israel Sapir, E. -Dr. E. Yagev (1995): ”Drip Irrigation”. Ministry of Agriculture and Rural Development, CINADCO, Ministry of Foreign Affairs, MASHAV, Israel Sapir, E. -Dr. E. Yagev (2001): ”Sprinkler Irrigation”. Ministry of culture and Rural Development, CINADCO, Ministry of Foreign Affairs, MASHAV, Israel Eng. Nathan, R. (2002): ”Fertilization Combined with Irrigation (Fertigation)”. Ministry of Agriculture and Rural Development, CINADCO, Ministry of Foreign Affairs, MASHAV, Israel