Rice production with less irrigation water is possible in a Sahelian environment

We investigated the possibility of saving irrigation water in rice production in a Sahelian environment with different nitrogen rates and weed control treatments. A series of field experiments was conducted at Ndiaye (shallow water table, dry and wet season) and at Fanaye (deep water table, wet season) in Senegal with four irrigation treatments, involving three water-saving regimes using alternate wetting and drying (AWD) and a flooded control, and three weed management treatments. This was followed by two experiments with the same four irrigation treatments in combination with three nitrogen (N) application rates, at the same locations. Hence four irrigation regimes were tested over three seasons. Between 480 and 1060 mm of irrigation water was used in the water-saving treatments compared with 800-1490 mm in the flooded-rice treatment. Rice yields ranged from 2.3 to 11.8 t ha(-1) in the water-saving treatments, whereas in the flooded control the yields ranged from 3.7 to 11.7 t ha(-1). In the wet season (WS), the treatments in which AWD was applied during part of the season resulted in the highest yields at both sites. In the dry season (DS), the continuously flooded treatment out-yielded other treatments, with the exception of AWD in Fanaye. At the Ndiaye site, the control of weeds increased yields from on average 2.0 to 7.4 t ha(-1) in the DS and from 1.4 to 4.9 t ha(-1) in the WS. No weed control in combination with AWD during the vegetative stage reduced yields to below 1.0 t ha(-1). However, when weeds were controlled, crop yields obtained with a combination of AWD and flooding were comparable with those obtained in fully flooded plots receiving the same weed management at both sites in the 2005 WS. Increasing rates of N significantly increased grain yield. Internal N efficiency was poorer at Ndiaye than at Fanaye suggesting that yields in Ndiaye are constrained by other factors than N. In Ndiaye, agronomic N use efficiency was smaller in the AWD treatments compared with fully flooded conditions. This study demonstrates that it is possible to save irrigation water and improve water productivity in rice grown in a Sahelian environment. An irrigation regime for rice that starts as conventional (flooded), and then changes to AWD can save water with little or no yield loss, while maintaining low weed pressure and efficient use of N. (C) 2009 Elsevier B.V. All rights reserved.