Archive for June, 2012

Rice Science Vol. 19 No. 2:143-152. 2012

Estimating Crop Coefficient in an Intermittent Irrigation Paddy Field using Excel Solver

Chusnul ARIF, Budi Indra SETIAWAN, Hanhan Ahmad SOFIYUDDIN, Lolly Martina MARTIEF, Masaru MIZOGUCHI, Ryoichi DOI


The current study proposes a novel method using Excel Solver to estimate, from limited data, crop coefficient (Kc) in paddy field under intermittent irrigation (II). The proposed method was examined in a field experiment conducted at Karang Sari Village, Bekasi, West Java, Indonesia during the first rice season of 2007/2008 (December 2007 to April 2008) in the rainy season. As the control, continuous flooding irrigation (CF) was applied to the conventional rice cultivation fields. Based on the observed water storage, Excel Solver was used to estimate crop evapotranspiration. Estimated crop evapotranspiration was used to compute Kc value, then the average Kc value in each growth stage was compared with that for the CF treatment. The estimation method was evaluated by comparing estimated crop evapotranspiration and the crop evapotranspiration derived by the well established FAO procedure. Excel Solver estimated crop evapotranspiration accurately with R2 values higher than 0.81. Accordingly, more than 81% of the FAO crop evapotranspiration was described by the proposed method. Thus, Kc value could be well determined from those estimated crop evapotranspiration. Under the II treatment, the average Kc values were 0.70, 1.06, 1.24 and 1.22 for the initial, crop development, reproductive and late season stages, respectively. These values were lower than those under the CF treatment for initial and crop development stages because of a minimal soil evaporation and intense dryness during these stages. However, average Kc values under the II treatment were higher than those under the CF treatment in the reproductive and last season stages, indicating that the II treatment promoted more plant activity particularly for dry biomass production as indicated by a greater number of tillers per hill.

Keywords: crop coefficient, evapotranspiration, intermittent irrigation, excel solver, water balance