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Maize (Zea mays L.) is an important food crop for irrigated perimeters of the African Sahel. Large demand and limited water availability often results in deficit irrigation. Increasing cost of two controllable production inputs-water and nitrogen (N) further demands their efficient use. In a 2 year field study, maize was grown under five irrigation treatments, providing deficit irrigation during vegetative and reproductive periods at five N levels on a Tropudalph clay loam soil. The purpose of this study was to (i) determine effect of timing and frequency of deficit irrigation and N on maize yield and yield components and, (ii) evaluate the interaction of deficit irrigation and N on evapotranspiration (ET) and water use efficiency (WUE) under a semi-arid Sahelian environment.

When two deficit irrigations during the vegetative period were imposed, grain yield was numerically reduced by 11.1 and 6.6% in 1996/1997 and 1997/1998 seasons, respectively. When deficit irrigation occurred during the vegetative stage and early reproductive stage, significant yield reductions of 22.6 and 26.4% were found for the respective seasons. Imposition of sixer eight deficit irrigations during vegetative and reproductive phases reduced grain yield by up to 52% over all N levels. Yield reductions were associated with reduction in kernel numbers and to a lesser extent, kernel weight. Thus, grain yield reduction was nearly proportional to duration of deficit irrigation imposed during the season.

Grain yield response to N rate was usually quadratic and differed with the level of deficit irrigation. Conversely, yield reduction to water shortage was much more severe at high N rates. Full irrigation (weekly) at 160 kg N/ha, resulted in ET of 641 and 668 mm in 1996/1997 and 1997/1998, respectively, while maximum deficit irrigation reduced ET to 275 and 281 mm at 80 kg N/ha in 1996/1997 and 1997/1998, respectively. Nitrogen supply modified water use at all irrigation levels. Deficit irrigation during any reproductive growth stage in maize would not be feasible if an individual farmer’s goal is to maximize economic yield in the Sahel. However, if the irrigation goal is to cover a larger area for more equitable benefit to more producers who are limited with available water, deficit irrigation may be feasible during the vegetative phase for maize. (C) 2000 Elsevier Science B.V. All rights reserved.