Water and nitrate dynamics under irrigated onion in a semi-arid area

An experiment is being undertaken on the site of Kamboinse (Burkina Faso) to study the dynamics of irrigation water and nitrates in and under the root zone of an irrigated onion crop. The goals of the research are to follow nitrate and water transfer, to study the influence of the irrigation amount on the losses of water and nitrates and to evaluate the contribution of simulation models for improving decision support and management of water and nitrogen fertilizers in semi-arid climatic conditions. The crop under consideration is onion subjected to three different treatments: (i) application of optimal amounts of irrigation and fertilizers, (ii) application of the amounts used traditionally by local farmers and (iii) control treatments so as to evaluate natural nitrate supply and transformations. The final goal is to define appropriate amounts of irrigation and nitrogen supply in order to prevent leaching. The first results show that optimal irrigation and fertilizer supply leads to considerably fewer losses than in the case of traditional supply; nitrate leaching is double and water losses are up to three times higher in the latter case. The amount of nitrogen measured in the soil after harvest is very small. Copyright (C) 2002 John Wiley Sons, Ltd.