Deficit irrigation and nitrogen effects on maize in a Sahelian environment: II. Shoot growth, nitrogen uptake and water extraction

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Abstract

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 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.

Introduction

There has been an increasing interest in scheduling deficit irrigation in order to conserve water and maintain crop productivity in the Sahel of West Africa. In these areas, total biomass production is often as important to farmers as grain since animals are a significant part of their livelihood. We reported on the effect of seasonal water deficit and nitrogen (N) rate on grain yield and yield components (Pandey et al., 2000). This research suggested that irrigation deficit during the vegetative stages of maize (Zea mays L.) growth was possible without sacrificing significant grain yield. This irrigation response was dependent on the N application rate. Research has shown the importance of water and N interactions in optimizing maize productivity (Eck, 1984, Eghball and Maranville, 1993a). Most studies suggest that water shortage during vegetative growth reduces leaf area (Boyer, 1970, Acevedo et al., 1971, NeSmith and Ritchie, 1992, McCullough et al., 1994), internode elongation (Novoa and Loomis, 1981), and leaf and stem weight (Denmead and Shaw, 1960, Eck, 1984). In a field study conducted under semi arid environment of Texas, water deficits imposed 41 days after planting reduced leaf, stalk and ear yields of maize, while those imposed 55 days after planting reduced only stalk and ear yields. Water deficit during grain filling did not affect leaf and stalk yields (Eck, 1984). Management of water shortage through frequency and quantity of irrigaiton water during vegetative growth and/or reproductive growth merits attention in high evaporative environments to minimize curtailment of crop growth and yield and achieve higher water use efficiency (Eck, 1985, Chapman and Barreto, 1997).

Nitrogen requirement by maize compared with other nutrients is large in Sahelian soils for optimum vegetative and reproductive growth. Many physiological processes associated with maize growth are enhanced by N supply (Eck, 1984). Nitrogen has dramatic effects on maize growth, development and grain yield on soils that are limiting in N supply. Numerous studies have shown the effects of reduced N supply on leaf area index (LAI), plant height, shoot weight and plant N uptake (Eck, 1984, Pandey et al., 1984, Muchow, 1988, McCullough et al., 1994). In most maize producing areas, increasing rate of N supply results in greater LAI and leaf N (McCullough et al., 1994). Variation in N supply affects crop growth, development and potential kernel set and grain yield (Greenwood, 1976, Pandey et al., 2000). Leaf area index, leaf area duration, crop photosynthetic rate, radiation interception and radiation use efficiency are increased by N supply (Muchow, 1988). Reduced N supply decreases crop growth (Cox et al., 1993); however, N response is modified by water supply under field condition (Greenwood, 1976, Pandey et al., 2000). Variable water supply either due to shortage of water or failure of the irrigation system to supply water during vegetative and/or reproductive growth stages in many irrigated areas of sub-Saharan Africa, particularly in the Sahel, is common and often results in deficit irrigation.

Information on frequency and quantity of irrigation water and effect of deficit irrigation on shoot and root growth of maize and the subsequent water and N extraction patterns have not been well elucidated under the stressful Sahelian environment, more so with differential rates of N supply. Further, information on crop growth responses and morphological/physiological yield determinants are needed to analyze crop productivity that relate to crop water production function and economic returns. The objectives of this study were to (i) determine the effects of timing and duration of deficit irrigation on maize shoot growth and water extraction, (ii) evaluate water deficit and N rate effects on N uptake, and (iii) analyze relationships between grain yield, plant growth and deficit irrigation and N supply.

Section snippets

Materials and methods

A field experiment was conducted for 2 years (1996–1997 and 1997–1998) at INRAN (Institut National de Recherche Agrononmique du Niger) research station near Konni (lat. 11°N, long. 12°E) on a Tropudalph clay loam soil (fine kaolintic thermic kanolic tropudalph). The site description, crop culture, and weather conditions were previously described (Pandey et al., 2000). Water deficits were imposed as previously described (Pandey et al., 2000). Irrigation was withheld at various crop growth stages (

Aboveground biomass

Aboveground biomass production was different each season and presented separately in Table 1. There was less differential in biomass production between zero N and 160 kg ha−1 in 1996/1997 than in 1997/1998. The greater rates of N in 1997/1998 resulted in markedly more biomass production than those rates in 1996/1997 and markedly less biomass at the low N rates for the second season. Response to applied N was quadratic each year. There was little difference, however, between the two seasons for

Conclusions

Maize is commonly grown in humid and subhumid tropics, but in Sahelian countries, it is grown either in high rainfall zones or with supplementary irrigation in low rainfall zones. Water limitation is a major constraint to maize production. High evaporative demand and warm temperatures expose the crop to water stress if irrigation is not adequately provided. Efficient production of maize where soils are extremely poor in N and where rainfall is highly variable, requires simultaneous attention to

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