Effect of year and fertilizer on water-use efficiency of pearl millet (Pennisetum glaucum) in Niger

A comprehensive study was conducted over a 4-year period (1984-87) to evaluate the water use, growth and yield responses of pearl millet (Pennisetum glaucum (L.) R. Pr.) cv. CIVT grown with and without fertilizer (30 kg P2O5 and 45 kg N ha(-1)) at the ICRISAT Sahelian Centre, Sadore, Niger. Our study showed significant year and fertilizer effects on the growth and yield of millet at the study site. Observed year effects were primarily due to the variations in the amount and distribution of rainfall in relation to the potential demand for water. During 1984, 1985 and 1987, total rainfall was below the long term average, while in 1986 it was above average. While the onset of rains (relative to the average date of onset) was early from 1984 to 1986, in 1987 the sowings were delayed by as much as 33 days. Of all the four years, the separation between the treatments in the cumulative evaporation is most evident for 1984, which was a drought year with below-average rainfall in all the months from June to September. Cumulative evaporation patterns in 1985 and 1986 were similar because of regular rains and high average rainfall per rainy day from June to October. In 1987, sowings were delayed until 15 July and only 6 9 mm of rainfall was received per rainy day in July. Hence cumulative evaporation was initially low and showed a significant increase only after two significant rain events in early August. There was a large response to fertilizer in all the years as small additions of fertilizer phosphate increased the soluble phosphate in the soil. Fertilizer application resulted in a small increase in water use (7-14%) in all years except 1987. Increased yield due to the application of fertilizer was accompanied by an increase in the water-use efficiency (WUE) in all the four years with the largest increase in 1985. The beneficial effect of fertilizers could be attributed to the rapid early growth of leaves which can contribute to reduction of soil evaporative losses and increased WUE. Over the four seasons, average increase in the WUE: due to the addition of fertilizer was 84%.