Deficit irrigation and nitrogen effects on maize in a Sahelian environmentI. Grain yield and yield components

Maize (Zea mays L.) is an important food crop for irrigated perimeters of t he African Sahel. Large demand and limited water availability often results in deficit irrigation. Increasing cost of two controllable production inpu ts-water and nitrogen (N) further demands their efficient use. In a 2 year field study, maize was grown under five irrigation treatments, providing de ficit irrigation during vegetative and reproductive periods at five N level s on a Tropudalph clay loam soil. The purpose of this study was to (i) dete rmine effect of timing and frequency of deficit irrigation and N on maize y ield and yield components and, (ii) evaluate the interaction of deficit irr igation and N on evapotranspiration (ET) and water use efficiency (WUE) und er a semi-arid Sahelian environment. When two deficit irrigations during the vegetative period were imposed, gra in yield was numerically reduced by 11.1 and 6.6% in 1996/1997 and 1997/199 8 seasons, respectively. When deficit irrigation occurred during the vegeta tive stage and early reproductive stage, significant yield reductions of 22 .6 and 26.4% were found for the respective seasons. Imposition of sixer eig ht deficit irrigations during vegetative and reproductive phases reduced gr ain 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. Thu s, grain yield reduction was nearly proportional to duration of deficit irr igation 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, respective ly, 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 wat er 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 goa l is to cover a larger area for more equitable benefit to more producers wh o are limited with available water, deficit irrigation may be feasible duri ng the vegetative phase for maize. (C) 2000 Elsevier Science B.V. All right s reserved.