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 nort hwest China has led to the urgent need to reduce irrigation. Regulated defi cit irrigation (RDI), i.e. a controlled soil water deficit applied at certa in 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 experi ment on maize crops for 2 years (1996-1997) in this area. Controlled soil w ater deficit, either mild (50-60% of field capacity) or severe (40-50%), wa s applied at both the seedling and the stem-elongation stages. Stomatal resistance and leaf photosynthesis of water-stressed plants rapidl y recovered to the control level 3 days after rewatering if such regulated water deficit was applied at the seedling stage. Controlled soil water defi cit also inhibited the stem-elongation, stimulated root system development and therefore resulted in a substantially enhanced root-to-shoot ratio. Soi l water deficit at the seedling stage apparently had no significant influen ce 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 s tage was substantially reduced by the soil drying at the stem-elongation st age. 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 mil d 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 st em-elongation stage is the optimum irrigation method for the maize producti on in this semi-arid area. (C) 2000 Elsevier Science B.V. All rights reserv ed.