Evapotranspiration and water-use efficiency of irrigated colored cotton cultivar in semiarid regions

Abstract

Irrigation studies provide a framework for evaluating agricultural production and the water resource management in locations where water is scarce. Field experiments were conducted at Barbalha- CE (northwestern Brazil) during 2004 and 2005 cropping seasons to investigate the effects of different irrigation water depths on the water-use efficiency and yield of the BRS 200-brown cotton cultivar (Gossypium hirsutum L.). Three irrigation treatments were applied: T1 = 80%; T2 = 100% and T3 = 120% of the potential evapotranspiration (ETp). The Bowen ratio-energy balance was used to obtain crop evapotrnaspiration (ETc) while daily reference evapo-transpiration (ETo) was obtained by the Penman-Monteith approach. Irrigation water was applied by a sprinkler system during both cropping seasons. The daily evapotranspiration ranged from 2.59 mm·day-1 at the emergence to 5.89 mm·day-1 at first square growth stage with an accumulated value of 528.7 mm as a mean of the two cropping seasons. The average crop coefficient across both years (2004-2005) was 0.90, with minimum and maximum values of 0.46 and 1.17 at emergency and first flower growth stages, respectively. The results also showed that the increase in irrigation from 80% to 120% of ETp resulted in a significant increase in the seed-cotton yield (from 2476.0 to 3289.5 kg·ha-1), while lint percentage and water-use efficiency (WUE) were slightly reduced from 35.7% to 35.6% and from 0.60 to 0.53 kg·m-3, respectively. These results suggests that the cotton crop (cultivar BRS-200 brown) reaches higher water-use efficiency when irrigated with 80% of the crop evapotrnaspiration obtained as a function of the reference evapotranspiration and the crop coefficient proposed by FAO. However, the maximum seed-cotton yield is obtained when irrigated with 120% of that crop evapotranspiration.