Determination of evapotranspiration and crop coefficients for bush okra (Corchorus olitorius) in a sub-humid area of Nigeria

Abstract

A two-year field experiment was carried out to determine crop evapotranspiration (ETc) and crop coefficients (Kc) for irrigated bush okra (Corchorus olitorius) at Minna in a tropical sub-humid area of Nigeria between February and April of 2008 and 2009. Eight 4 x 1 m check basins were laid out in a randomized complete block design with two treatments and four replications. The two common local varieties of C. olitorius(Amugbadu and Oniyaya) constituted the treatments. The soil moisture depletion method was used to determine ETc while potential evapotranspiration (ETp) was calculated on a daily basis using Blaney-Morin-Nigeria (BMN) evapotranspiration model developed for Nigerian environmental conditions. Kc values were derived as dimensionless ratios of ETc to ETp on a weekly basis. Across varieties and cropping periods, average weekly ETc ranged from 2.0 to 6.8 mm day-1 while seasonal ETc ranged from 326 to 374 mm, withAmugbadu having significantly higher seasonal ETc (P≤0.01) in each cropping period, presumably because of its spreading growth habit. Weekly Kc values rose from a minimum of 0.38 at the initial stage of crop growth to a peak value of 1.05 at the mid-season stage and dropped to 0.40 at the end of the late season stage. Closer spacing of Oniyaya, which has an erect growth habit, is recommended in order to increase its ground coverage, ETc and fresh leaf yield, under sole cropping system. Key words: Corchorus olitorius, Amugbadu, Oniyaya, evapotranspiration, crop coefficients.