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 Permanent wilting Gravitational water Rapid drainage Capillary water Slow drainage Hygroscopic water Essentially no drainage Available moisture Unavailable moisture
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, K S is the Darcy coefficient of proportionality.
Soil-water-plant relationship K S in saturated soil is the following: K nS in unsaturated soil is the following: where hG 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 zone extraction Depth D 40% 30% 20% 10% D/4 10 3 0 20 30 40 Soil depth [cm] 7.4% 68.7% 10.3% 9.4% 4.2% Water distribution in the soil Root distribution in the various soil layers
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 F c 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 P w 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 1m 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 IrI 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 Fc=17[%] Wilting pointPw=7 [%] Soil density S =1.3[g/cm 3 ] Water density W =1.0[g/cm 3 ] Main root zoneZr=0.4[m]
Soil-water-plant relationship 1.Available water by volume: 2.The depth of available water for a 1m 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 Depth Layer thickness Soil texture FcPw SS [cm][m][%w] [g/cm 3 ] 10-200.2Sandy- loam 1351.5 220-350.15loam2081.4 335-650.30Clay- loam 27131.4 465-1100.45clay32161.3
Soil-water-plant relationship The applied equation is Fc-Pw [%] S [g/cm 3 ] Zr [m] AWDZr [mm/layer] 13-51.50.2 20-81.40.15 27-131.40.3 32-161.30.1 AWDZr(Zr=0.75m) 24.0 25.2 58.8 20.8 128.8
References Azenkot, A.(1998):”Design Irrigation System”. Ministry of Agricul- ture 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 Agricul- ture 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