Irrigation Department, Shiraz University, Shiraz, I.R of Iran (At present, faculty member of Ardakan University).
Water, salinity and nitrogen are the major factors affecting maize production in
arid and semi-arid areas. The objectives of this study were to investigate the effects
of different water, salinity and nitrogen levels on yield-water relationships, water
use, water productivity (WP), water use efficiency (WUE) and water uptake
reduction function by maize hybrid SC-704 in a semi-arid area and silty clay loam
soil. A split-split-plot design with three replications in two years of 2009 and 2010
was conducted. The different levels of irrigation water considered as main plot,
salinity of irrigation water as sub-plot and nitrogen fertilizer rate as sub-sub-plot.
Irrigation treatments consisted of I1 (1.0ETc+0.25ETc as leaching), I2 (0.75I1) and I3
(0.50I1) applied at 7-day intervals. The salinity treatments of irrigation were 0.6
(fresh water), 2.0 and 4.0 dS m-1. There were also three nitrogen (N) treatments
including 0, 150 and 300 kg N ha-1. Results showed that the actual crop ET and
transpiration (T) were significantly less in I3 as compared to I1 treatments as 42 and
43%, respectively. Besides, T values under S3 were statistically less than that in S1
treatment as 12%. The soil evaporation (E) values were 26, 31 and 27% of ET at I1,
I2 and I3 treatments, respectively and its values significantly increased with
increasing salinity levels of irrigation water. The minimum and maximum amount
of E occurred at I3S1N3 and I1S3N3, respectively. The study showed that deficit
irrigation as 0.50I1 and 0.75 I1 were the optimum levels of irrigation to access the
highest WP and WUE for dry matter (DM) and grain yield (GY) respectively.
Besides, S1 was the optimum treatment for achievement of highest WP and WUE
for DM and GY. Results also indicated that the optimum treatment for WP and
WUE for GY was I2S1N3. Furthermore, N fertilization could not statistically
improve WP and WUE beyond 150 kg N ha-1. The yield response factor to water
showed that maize GY was more sensitive to water than its DM. Results also indicated that the Homaee and Feddes (1999) equation was resulted in acceptable
estimation of root-water uptake reduction function [α (h,ho)]. Furthermore, results
showed that the FAO method underestimated the maize yield (DM/GY) at different
N application rates: however, the Homaee and Feddes (1999) method resulted in
acceptable prediction of the maize GY. Therefore, Homaee and Feddes (1999)
equation is recommended for estimation of both α (h, ho) and maize GY. Keywords: Maize; Nitrogen levels; Root-water uptake reduction function; Salinity
levels; Water use efficiency; Yield-water relationships.