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.
Highlights
Agriculture is largely responsible for the increase in world water consumption due to the worldwide increases in agricultural irrigation areas that were needed to maintain a satisfactory level of food production for the human population
Increasing crop water-use efficiency (WUE) to increase agricultural production without increasing the volume of water that is used for irrigation has become more challenging for these regions
Some studies have shown that an increase in irrigation water volume does not necessarily result in crop yield increases [1,2], but WUE values generally decrease with increasing irrigation water levels for all productivity parameters [3]
Summary
Agriculture is largely responsible for the increase in world water consumption due to the worldwide increases in agricultural irrigation areas that were needed to maintain a satisfactory level of food production for the human population. Increasing crop water-use efficiency (WUE) to increase agricultural production without increasing the volume of water that is used for irrigation has become more challenging for these regions. Some studies have shown that an increase in irrigation water volume does not necessarily result in crop yield increases [1,2], but WUE values generally decrease with increasing irrigation water levels for all productivity parameters [3]. There is an urgent need in the agricultural sector to use dwindling water resources efficiently to enhance WUE at the farm level [5]. These authors have observed that the water-use efficiency could be enhanced by reducing evapotranspiration through irrigation deficit and by identifying the crop growth stage that is most sensitive to water stress
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