Effects of nitrogen and irrigation on water use of maize crops

Abstract

The possibility of improving the water use efficiency (q) of maize crops by applying fertiliser N was tested under irrigated and rainfed conditions. Three field experiments were undertaken in 2 years using a split-plot design with watering regimes (rainfed and irrigation) as main plots and N (0 and 100 kg N ha-1) as sub-plots. Evapotranspiration (ET) was determined by monitoring soil moisture content at 7-day interval using a neutron probe, soil evaporation (Esc) was measured daily using microlysimeters, and transpiration (T) was calculated by difference. Crop leaf area was measured at the mid-vegetative and at the early reproductive phase, and crop biomass and yield determined at harvest maturity. Application of 100 kg N ha-1 increased biomass in the three sowings by 25-42%, but grain yield was increased only in Experiment I (68%) and Experiment II (43%). Irrigation increased biomass by 46 and 21% in Experiments I and II, respectively. The increase in grain yield due to irrigation was significant only in the driest sowing (59%). Application of 100 kg N ha-1 increased q in the three sowings by 18-33%, due to a reduction in Esc and a concurrent increase in T. In the driest sowing, the decrease in Esc due to N application was greater under irrigation than under rainfed conditions. Application of 100 kg N ha-1 increased T by increasing the size of the crop leaf canopy and the volume of water extracted from a soil depth of 0.6-1.0 m. The decrease in Esc was due to a larger leaf canopy with fertiliser N. Transpiration efficiency (TE) was not affected by N application. Therefore, the water use efficiency of maize was increased by application of fertiliser N, but reductions in Esc were less in dry compared with irrigated sowings. © 2002 Elsevier Science B.V. All rights reserved.