Single and dual crop coefficients and crop evapotranspiration for wheat and maize in a semi-arid region
- PDF / 800,104 Bytes
- 16 Pages / 595.276 x 790.866 pts Page_size
- 72 Downloads / 196 Views
ORIGINAL PAPER
Single and dual crop coefficients and crop evapotranspiration for wheat and maize in a semi-arid region M. H. Shahrokhnia & A. R. Sepaskhah
Received: 14 December 2011 / Accepted: 25 January 2013 # Springer-Verlag Wien 2013
Abstract In this study, weighing lysimeters were used to investigate the daily crop coefficient and evapotranspiration of wheat and maize in the Fars province, Iran. The locally calibrated Food and Agriculture Organization (FAO) Penman–Monteith equation was used to calculate the reference crop evapotranspiration (ETo). Micro-lysimetry was used to measure soil evaporation (E). Transpiration (T) was estimated by the difference between crop evapotranspiration (ETc) and E. The single crop coefficient (K c ) was calculated by the ratio of ETc to ETo . Furthermore, the dual crop coefficient is composed of the soil evaporation coefficient (Ke) and the basal crop coefficients (Kcb) calculated from the ratio of E and T to ETo, respectively. The maximum measured evapotranspiration rate for wheat was 9.9 mmday−1 and for maize was 10 mmday−1. The total evaporation from the soil surface was about 30 % of the total wheat ETc and 29.8 % of total maize ETc. The single crop coefficient (Kc) values for the initial, mid-, and end-season growth stages of maize were 0.48, 1.40, and 0.31 and those of wheat were 0.77, 1.35, and 0.26, respectively. The measured Kc values for the initial and mid-season stages were different from the FAO recommended values. Therefore, the FAO standard equation for Kc-mid was calibrated locally for wheat and maize. The Kcb values for the initial, mid-, and end-season growth stages were 0.23, 1.14, and 0.13 for wheat and 0.10, 1.07, and 0.06 for maize, respectively. Furthermore, the FAO procedure for single crop coefficient showed better predictions on a daily basis, although the dual crop coefficient method was more accurate on seasonal scale.
M. H. Shahrokhnia : A. R. Sepaskhah (*) Irrigation Department, Shiraz University, Shiraz, Iran e-mail: [email protected]
1 Introduction Knowledge of crop water requirement is necessary for agricultural water management and irrigation scheduling in hydrological studies and field management (Kjaersgaard et al. 2008). This is directly related to an accurate estimation of crop evapotranspiration (ETc) which depends on crop characteristics and development stage, weather parameters, environmental conditions, and management practices. Crop ETc can be obtained from direct and indirect estimation methods. In the direct method, ETc is measured using lysimeters, while the indirect method refers to ETc estimation based on the reference evapotranspiration (ETo) and a crop coefficients (Kc). In comparison with the indirect method, the direct crop ETc determination method is more difficult, usually expensive, and not applicable everywhere. The crop coefficient (Kc) has been introduced as an important parameter for calculating crop evapotranspiration (Allen et al. 1998; De Medeiros et al. 2001, 2005; Er-Raki et al. 2007; Williams and Ayars 2005
Data Loading...
