De®cit irrigation and nitrogen effects on maize in a Sahelian environment II. Shoot growth, nitrogen uptake and water extraction

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 subjected to different periods of de®cit irrigation and rates of N in the ®eld on a medium-deep Tropudalf clay loam soil. Water de®cit effects on shoot growth, N uptake and water extraction with varying level of N supply were analyzed to determine their inter-relationships. Water de®cit 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. De®cit 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 ®rst season during vegetative growth. When de®cit 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 de®cit was obtained at 120 kg N in 1996/1997 and at 160 kg N haÿ1 in 1997. Nitrogen uptake was more dependent on applied N than water supply although N uptake decreased with greater water and N de®cits. Water extraction was highest at the 120 and 160 kg N haÿ1 rates with soil water de®cit. Agricultural Water Management 46 (2000) 15±27 * Corresponding author. Present address: Department of Agronomy, 102 KCR Lab, University of Nebraska, Lincoln, NE 68583-0817 USA. Tel.: ‡1-402-472-3057; fax: ‡1-402-472-3654. E-mail address: [email protected] (J.W. Maranville). 1 Agronomist, Program Leader and technician, PNRA/INRAN, PB 429, Niamey. 2 Professor, University of Nebraska, Lincoln, NE. 0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 3 7 7 4 ( 0 0 ) 0 0 0 7 4 3 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 de®cit 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 pro®le, 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. # 2000 Elsevier Science B.V. All rights reserved.