Water use and yield of maize with two levels of nitrogen fertilization in SW Spain

Maize (cv. Prisma), managed with furrow irrigation was cropped consecutively for three years under Mediterranean management practices in the Guadalquivir river valley of SW Spain. Two N fertilization rates were used in different subplots: Subplot A had 510 kg N ha(-1) yr(-1), a rate widely used in the area. Subplot B at 170 kg N ha(-1) yr(-1), was one third of this. The water balance components and crop response to the irrigation regime were quantified to determine the efficiency of furrow irrigation practices in the area. Furthermore we sought to establish whether a reduced N fertilization rate would have any influence on the crop yield. No consistent differences were observed between subplots in any of the water balance components. Measured crop evapotranspiration (ET(c)) averaged 6250 m(3) ha(-1). Water losses by drainage were usually below 20% of ET(c). Soil evaporation under the canopy (E) was measured by using a specially-designed microlysimeter. Root density, soil water content and soil bulk density inside the microlysimeters were similar to those measured in the surrounding soil. Average values of E between two irrigations when the crop was fully mature amounted for 18-20% of ET(c). A maximum value of 1.6 for the crop coefficient (K-c) was calculated after using the Penman-Monteith combination equation for the calculation of the reference evapotranspiration (ET(c)). A standard formulation was used for the resistance term, which might account for the large value of K-c. Measurements of crop development parameters (height, leaf area index and phenological stage) showed some differences between subplots during the growing period, but no final differences were detected. No differences in yield were observed during the course of the study. Monitoring of physiological parameters (leaf water potential, leaf conductance and net photosynthesis rate) showed that water relationships of maize were not affected by the reduced N fertilization.