TEMPERATURE AND SOIL-WATER STATUS EFFECTS ON RADIATION USE AND GROWTHOF PEARL-MILLET IN A SEMIARID ENVIRONMENT

In semi-arid environments, crops are frequently subjected to a combina tion of high air temperatures, large atmospheric saturation vapor pres sure deficits, high soil temperatures and reduced soil water status. T o explore the performance of pearl millet (Pennisetum typhoides S. and H., cv. CIVT) from panicle initiation to flowering (GS 2) when grown in the field under combinations of these conditions, experiments were conducted in northern Nigeria in three seasons in which daily mean air temperatures during 18 days of this stage averaged 22, 27 and 33 degr ees C, and saturation vapor pressure deficits averaged 3.7, 4.0 and 5. 2 kPa, respectively. In each experiment, half of the crop was irrigate d, while the other half received no water after panicle initiation. Fo r irrigated millet, radiation use efficiency (RUE) did not vary signif icantly (P = 0.05) for the three experiments (1.7 g MJ(-1)). RUE of no n-irrigated millet was significantly reduced (0.8 g MJ(-1)) only durin g the season with the highest temperature. Radiation interception as a function of thermal time was similar in the irrigated and non-irrigat ed treatments except in the season with the highest temperatures, when radiation interception was reduced about 25% in the non-irrigated rel ative to the irrigated treatment. Stem extension of non-irrigated mill et did not decline relative to irrigated millet, despite the almost co mplete extraction of plant available water in the upper 30 cm of the s oil, except during the season with the highest temperatures, when stem extension rates began to decline as soon as water was withheld. Under high air temperatures and saturation vapor pressure deficits, dry mat ter accumulation in both irrigated and non-irrigated millet during GS 2 could be reasonably predicted from RUE and radiation interception. H owever, when high soil temperatures (daily mean at 5 cm of 34 degrees C) occurred in the nonirrigated treatment, both RUE and radiation inte rception decreased relative to all other treatments.