Determination of Optimum Irrigation Time during the Day by Using Plant Based Measurements

Indicators based on plants used extensively in recent years for the purpose of determining irrigation time. in this study leaf water potential (lwp) and crop water stress index (cwsi) were used to determine irrigation time based on plant. surface drip (di) and subsurface drip systems (sdi); two irrigation frequencies (if3: 3-day; if6: 6-day) and four irrigation regimes (full irrigation, fi; deficit irrigations, ks50; ks75; and partial root-zone drying prd50, which received, respectively 50, 75 and 50% of fi) were tested in a split-split plot design. lwp was measured using the pressure chamber and cwsi values were computed using canopy temperature (tc) and air temperature (ta) measured with an infrared thermometer. at the same time wet and dry air temperatures were measured with a psychrometer thermometer. both measurement were taken between 08.00 and 17.00 hours during the day. the cwsi values which were lower in the early hours of the day were found to rise towards the middle of the of the day and tended to fall again towards the evening hours in both irrigation methods. however, contrary to cwsi values, lwp values were found to be higher in the early hours of the day, falling in mid-day and tending to rise again in the evening. compared with surface drip irrigation, cwsi and lwp values lower than that of the subsurface drip irrigation method. plants in the middle of the day with a maximum stress was observed with the cws and ysp measurements. it is recommended to make the plant early or late on the day when the plant has the least stress.