Determining Water-Yield Relationship, Water Use Efficiency, Seasonal Crop and Pan Coefficients for Alfalfa in a Semiarid Region with High Altitude

Y. KUSLU, U. SAHIN, T. TUNC and F. M. KIZILOGLU

Ataturk University, Faculty of Agriculture, Department of Agricultural Structures and Irrigation, 25240 Erzurum, Turkey

Abstract

KUSLU, Y., U. SAHIN, T. TUNC and F. M. KIZILOGLU, 2010. Determining water-yield relationship, water use efficiency, seasonal crop and pan coefficients for alfalfa in a semiarid region with high altitude. Bulg. J. Agric. Sci., 16: 482-492

A field study was conducted to determine effects of seasonal deficit irrigation on plant dry forage yield and water use efficiency of alfalfa for a 2-year period in the semiarid region with high altitude. In addition, the seasonal crop and pan coefficients kc and kp of alfalfa was determined in full irrigation conditions. Irrigations were applied when approximately 50% of the usable soil moisture was consumed in the effective rooting depth at the full irrigation treatment. In deficit irrigation treatments, irrigations were applied at the rates of 80, 60, 40, 20 and 0% of full irrigation treatment on the same day. Irrigation water was applied by hose-drawn traveler with a line of sprinklers. Seasonal actual evapotranspiration, total dry forage yield and water use efficiency was the highest in full irrigation conditions and the lowest in continuous stress conditions. The linear relationship between seasonal actual evapotranspiration and total dry forage yield was obtained. According to the averaged values of 2 years, yield response factor (ky) was 1.33. Both seasonal kp and kc were determined as 0.86 for alfalfa, when combined values of 2 years.

Key words: Alfalfa; crop coefficient; pan coefficient; water deficit; yield response factor

Abbreviations: ETo - reference evapotranspirasyon (mm); ky - seasonal yield response factor; kc - seasonal crop coefficient; kp - seasonal pan coefficient; ETa - actual evapotranspiration, mm; I - the amount of irrigation water applied (mm); P – precipitation, mm; Cr - capillary rise (mm); Dw - amount of drainage water (mm); Rf - amount of runoff (mm); Δ S - change in the soil moisture content (mm); Ya - actual harvested yield; Ym - maximum harvested yield, ETm - maximum evapotranspiration, mm; Yd - relative yield reduction; ETd - relative evapotranspiration reduction, mm; Epan - evaporation of Class A pan, mm; Rn - net radiation at the crop surface, MJ m-2 day-1; G - soil heat flux density, MJ m-2 day-1; T - mean daily air temperature at 2 m height, °C; u2 - wind speed at 2 m height, m s-1; es - saturation vapour pressure, kPa; ea - actual vapour pressure, kPa; es - ea - saturation vapour pressure deficit, kPa; Δ - slope of the saturation vapour pressure curve, kPa/°C; γ - psychrometric constant, kPa/°C; WUE - water use efficiency, kg ha-1 mm-1

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