Plant water accessibility function: A design and management tool for trickle irrigation Alberto Colombo a, * , Dani Or b,1 a Departamento de Engenharia, Universidade Federal de Lavras, Lavras, Brazil b Department of Civil & Environmental Engineering, University of Connecticut, Storrs, CT, USA Accepted 25 July 2005 Available online 24 August 2005 Abstract Systematic evaluation of different trickle irrigation design and management scenarios must consider the impact of a particular design on crop response at different soils, climatic conditions, and management options. Anecdotal evidence suggests that different emitter arrangements, discharge rates, irrigation amounts, and soil types result in different patterns of crop yield distribution generally decreasing with distance from nearest emitter. We hypothesize that these design and management variables could be incorporated into a plant water accessibility (PWA) function relating characteristic crop yield response as a function of distance to the nearest emitter. A field experiment was conducted to test the hypothesis and estimate the necessary parameters. Field corn was drip irrigated using different combinations of emitter spacing (152 cm  175 cm, 152 cm  107 cm, and 152 cm  61 cm), emitter discharge (3.8 and 1.5 L/h) and irrigation interval (1, 3 and 7 days). Results show that corn dry matter yield remained constant up to certain distance, R E , from the nearest emitter, after which it gradually decreased up to distance R N , where corn yield was no different than for non-irrigated plants. Relationships were established between R E and average amount of water applied per irrigation (R 2 = 0.842); and between the reduction zone length (R N –R E ) and R E (R 2 = 0.879). These relationships were used to evaluate the impact of various design considerations on average corn yield. Simulated values and field observed values were in good agreement, demonstrating the potential usefulness of the proposed PWA function as a design and management tool for trickle irrigation systems. # 2005 Elsevier B.V. All rights reserved. Keywords: Trickle irrigation design; Crop yield; Emitter spacing; Irrigation interval www.elsevier.com/locate/agwat Agricultural Water Management 82 (2006) 45–62 * Corresponding author. Tel.: +1 55 35 3829 1481; fax: +1 55 35 3829 1482. E-mail address: acolombo@ufla.br (A. Colombo). 1 Tel.: +1 860 486 2768; fax: +1 860 486 2298. 0378-3774/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.agwat.2005.07.025