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Maize growth in arid and semiarid regions is often limited by variation in the amount and frequency of irrigation or rainfall. Sub-optimal supply of nitrogen (N) may further curtail growth and development of the crop. Simultaneous optimization of these two inputs provides optimum conditions for crop growth and productivity. A maize (Zea mays L.) crop was sudjected to different periods of deficit irrigation and rates of N in the field on a medium-deep Tropudalf clay loam soil. Water deficit effects on shoot growth, N uptake and water extraction with varying level of N supply were analyzed to determine their inter-relationships. Water deficit was created by withholding irrigation at different stages of crop development. Increasing moisture stress resulted in progressively less leaf area, crop growth rate (CGR), plant height, shoot dry matter and harvest index. Mean increase in above ground biomass was 7.7 and 8.7 kg per mm of water used in the 1996/1997 and 1997/1998 seasons, respectively. Deficit irrigation stress indices (DISI) for above ground biomass when the crop was subjected to a 2 week stress was 11.0 and 20.1 compared to 4 week stress values of 3.2 and 16.5 in the 1996/1997 and 1997/1998, respectively, indicating greater stress the first season during vegetative growth. When deficit irrigation was increased to 8 weeks, DISI values were 34.1 and 39.8 for the respective seasons. Biomass production response to N in both years was quadratic; however, N response differed with irrigation level in both seasons. Highest biomass yield with no irrigation deficit was obtained at 120 kg N in 1996/1997 and at 160 kg N ha(-1) in 1997. Nitrogen uptake was more dependent on applied N than water supply although N uptake decreased with greater water and N deficits. Water extraction was highest at the 120 and 160 kg N ha(-1) rates with soil water deficit.

This study showed that a maize crop differs in its ability to maintain LAI, CGR and above ground dry matter production at different levels of water deficit and N supply. The adaptive strategy of maize plants under vegetative water stress appears to be extended rooting depth and water extraction from the deeper soil profile, and simultaneous reduction in leaf area to decrease transpiration. Optimizing the inputs of water and N at the farm level would maximize biomass production and harvest index. This information can be useful to guide crop management strategy to enhance maize production in the irrigated perimeter of a Sahelian environment. (C) 2000 Elsevier Science B.V. All rights reserved.