EVALUATION OF WEEKLY PAN COEFFICIENTS (KP) FOR CLASS A PAN INSTALLED UNDER VARIOUS FIELD CONDITIONS COMPARING WITH KP'S RECOMMENDED BY FAO

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MORADI DALINI A.A.F.; NEYSHABOURI M.R.; JAHANBAKHSHASL S.; JAFARZADEH A.A.

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Journal: Iranian Journal of Soil Research Year:2000 | Volume:14 | Issue:2 Page(s): 164-175

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Title

EVALUATION OF WEEKLY PAN COEFFICIENTS (KP) FOR CLASS A PAN INSTALLED UNDER VARIOUS FIELD CONDITIONS COMPARING WITH KP'S RECOMMENDED BY FAO

Author(s)

MORADI DALINI A.A.F. | NEYSHABOURI M.R. | JAHANBAKHSHASL S. | JAFARZADEH A.A. | Issue Writer Certificate

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Abstract

In order to study the effects of field conditions on pan coefficient (Kp), three class A pans were installed at a small grass field (11 x11 m) according to FAO standards, and in an alfalfa field at 50 and 80 cm elevations (heights of pan rim from soil surface). The experiment was conducted in Tabriz University field research station at Karkage during J00 day crop growing periods (July 12-0ct 19, 1997). Weekly evapotranspirations from grass (ET°) were computed using water balance equation. Drainage component in the equation was assumed to be negligible. Evaporation from the three pans (Epg, Ep50 and Ep80) were measured every day. Weekly pan coefficients for each pan (Kpg, Kp50 and Kp80) were computed dividing ET° by the Ep from the corresponding pan. Kpg, Kp50 and Kp80 average values (during 100 days period) were 0.77, 0.75 and 0.69 respectively. The recommended Kp values by FAO were computed by following equation: Kp = 0.482 + 0.024LnF – 0.000376U + 0.0045H Where F is upwind fetch length in m, U is mean wind run at 2 m height in Km/day and H is the percentage of mean relative humidity of air. The average recommended weekly Kp value by FAO turned to be 0.67. Comparing weekly Kpg and weekly Kp values computed by FAO method indicated that this method under predicts the Kp's by about 12%. Therefore, using the recommended FAO Kp's may underpredict evapotranspiration and crop water requirement and therefore may lead to yield decrease.Comparing Kp50 and Kp80 values indicated significant variation between them, whereas the variation between Kpg and Kp50 values was no significant. Because of the similarity of Kp50 to Kpg values during most of the weekly periods and their averages, one may use calls A pan records installed at an alfalfa field to compute ET° by applying Kp50 values as determined in this investigation. Maintaining a field of grass as a pan site is more difficult and expensive than an alfalfa field, which in most locations is already available.

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APA: Copy

MORADI DALINI, A.A.F., NEYSHABOURI, M.R., JAHANBAKHSHASL, S., & JAFARZADEH, A.A.. (2000). EVALUATION OF WEEKLY PAN COEFFICIENTS (KP) FOR CLASS A PAN INSTALLED UNDER VARIOUS FIELD CONDITIONS COMPARING WITH KP'S RECOMMENDED BY FAO. IRANIAN JOURNAL OF SOIL AND WATERS SCIENCES, 14(2), 164-175. SID. https://sid.ir/paper/15913/en

Vancouver: Copy

MORADI DALINI A.A.F., NEYSHABOURI M.R., JAHANBAKHSHASL S., JAFARZADEH A.A.. EVALUATION OF WEEKLY PAN COEFFICIENTS (KP) FOR CLASS A PAN INSTALLED UNDER VARIOUS FIELD CONDITIONS COMPARING WITH KP'S RECOMMENDED BY FAO. IRANIAN JOURNAL OF SOIL AND WATERS SCIENCES[Internet]. 2000;14(2):164-175. Available from: https://sid.ir/paper/15913/en

IEEE: Copy

A.A.F. MORADI DALINI, M.R. NEYSHABOURI, S. JAHANBAKHSHASL, and A.A. JAFARZADEH, “EVALUATION OF WEEKLY PAN COEFFICIENTS (KP) FOR CLASS A PAN INSTALLED UNDER VARIOUS FIELD CONDITIONS COMPARING WITH KP'S RECOMMENDED BY FAO,” IRANIAN JOURNAL OF SOIL AND WATERS SCIENCES, vol. 14, no. 2, pp. 164–175, 2000, [Online]. Available: https://sid.ir/paper/15913/en

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