An improved water-use efficiency for maize grown under regulated deficit irrigation

The rapid decline of water resources on the semi-arid loess plateau in northwest China has led to the urgent need to reduce irrigation. Regulated deficit irrigation (RDI), i.e. a controlled soil water deficit applied at certain periods of a crop season, can save water and may maintain the yield. In this paper, the timing and the extent of RDI were studied in a field experiment on maize crops for 2 years (1996-1997) in this area. Controlled soil water deficit, either mild (50-60% of field capacity) or severe (40-50%), was applied at both the seedling and the stem-elongation stages. Stomatal resistance and leaf photosynthesis of water-stressed plants rapidly recovered to the control level 3 days after rewatering if such regulated water deficit was applied at the seedling stage. Controlled soil water deficit also inhibited the stem-elongation, stimulated root system development and therefore resulted in a substantially enhanced root-to-shoot ratio. Soil water deficit at the seedling stage apparently had no significant influence on the final grain yield, but the plants droughted at the seedling stage were better adapted to the later soil water deficit at the stem-elongation stage. Grain yield of plots that were well irrigated during the seedling stage was substantially reduced by the soil drying at the stem-elongation stage. However, the grain yield of those plots that were subjected to a soil drying at the seedling stage was not significantly reduced by a further mild soil drying (55% of field capacity at the minimum) at the stem-elongation stage. Grain yield of these plots was similar (no significant difference) to the always well-irrigated control. Water-use efficiency for these plots was substantially improved as a result. It is therefore recommended that a soil drying at the seedling stage plus a further mild soil drying at the stem-elongation stage is the optimum irrigation method for the maize production in this semi-arid area. (C) 2000 Elsevier Science B.V. All rights reserved.