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Cornell University (1992)

Water use in cereal crops in the semiarid tropics

McIntyre, Beverly Dianne

Titre : Water use in cereal crops in the semiarid tropics

Auteur : McIntyre, Beverly Dianne

Université de soutenance : Cornell University

Grade : Doctor of Philosophy (PhD) 1992

Variable and/or inadequate rainfall and high temperatures in the semi-arid tropics can markedly affect dry matter production in cereal crops. This study focused on the effect of these factors during the post-panicle initiation stage of canopy development. All experiments were conducted in Kano, Nigeria. Water was withheld from half of the treatments for at least 18 d, during which period the amount and pattern of soil water uptake, radiation interception, stem/leaf elongation, stomatal conductance (g$\sb\rm s$), predawn leaf water potential ($\psi\sb\rm leaf$), leaf area and dry weight were measured. The performance of millet (Pennisetum typhoides S. and H.), maize (Zea mays L.), and sorghum (sorghum bicolor L. Moench) were contrasted in one experiment, while that of millet planted at 2 different densities was contrasted in another. In a third experiment, characterized by high air and soil temperatures, only millet survived. Except under high soil temperatures (mean at 5 cm = 34$\sp\circ$C), dry matter production in millet could be adequately described as the product of intercepted radiation and the efficiency with which radiation is converted to dry matter (RUE averaged 1.6 g MJ$\sp-1$) during most of the 18 d period. At low planting densities, less radiation was intercepted by millet without an increase in RUE, resulting in less productivity. At the time water was first withheld, roots had reached a depth of 60 to 100 cm. Yet in all cases, water uptake occurred first in the upper horizons moving sequentially to lower horizons as the experiment progressed. Such patterns, along with decreases in g$\sb\rm s$ and $\psi\sb\rm leaf$ were well-predicted by a potential-driven water uptake model which presumed a static, exponential decrease in root density with depth. Model results suggested that increasing root density at depth would increase transpiration. Though both predicted and measured g$\sb\rm s$, surface soil water potential, and predawn $\psi\sb\rm leaf$ declined, stem elongation decreased only when soil temperature at 5 cm was high. These traditional indicators of stress were not accompanied during most of this period by a decrease in elongation or dry matter production except under high soil temperatures.

Mots clés : Agronomy, Agriculture, Sorghum bicolor, Nigeria, Pennisetum typhoides, Zea mays Biological sciences, Botany

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