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Lecture (13)

Lecture (13). Direct Measurement of ET : (Lysimeters). Change in soil moisture storage = (Inflow – Outflow) Δ S = (ID + P) – (DP + ET) in depth ; ID = IR × TR Drz (θ f – θ i ) = (ID + P) – (DP + ET)

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Lecture (13)

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  1. Lecture (13) Direct Measurement of ET :(Lysimeters)

  2. Change in soil moisture storage = (Inflow – Outflow) Δ S = (ID + P) – (DP + ET) in depth ; ID = IR × TR Drz (θf – θi) = (ID + P) – (DP + ET) Where, θi and θf = are measured initial and final soil moisture ID, P, and DP can be measured, then determine ET

  3. Selection of the Crop Coefficients: (Kc) Stage # 1 initial (germination) Stage # 2 crop development Stage # 3 Flowering (mid-season) Stage # 4 Fruits (later season) Factors affecting Kc are: • Crop characteristics (height, shape of leaves, ground coverage,..,etc) • Crop planting date • Length of the growing season • Rate of crop development

  4. Selection Approach • Initial Stage: for a given (predicted) irrigation frequency and predetermined Eto during this stage; obtain Kc from figure (4-8). • Mid-season stage : for a given climate (humidity and wind speed); select Kc from table (4-10). • For the end of the late season stage: select value of Kc from same table. • For given periods and dates of crop growing stages, plot the Kc-time function.

  5. Calculations of ET:

  6. Irrigation Frequency: • Irrigation frequency (irrigation intervals)varies along the growing season • For a fixed irrigation interval we need to vary ID (irrigation depth)

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