WATER-USE AND YIELD OF MAIZE WITH 2 LEVELS OF NITROGEN-FERTILIZATION IN SW SPAIN

Maize (cv. Prisma), managed with furrow irrigation was cropped consecu tively 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 r ate 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 t he irrigation regime were quantified to determine the efficiency of fu rrow irrigation practices in the area. Furthermore we sought to establ ish whether a reduced N fertilization rate would have any influence on the crop yield. No consistent differences were observed between subpl ots in any of the water balance components. Measured crop evapotranspi ration (ET(c)) averaged 6250 m(3) ha(-1). Water losses by drainage wer e usually below 20% of ET(c). Soil evaporation under the canopy (E) wa s measured by using a specially-designed microlysimeter. Root density, soil water content and soil bulk density inside the microlysimeters w ere similar to those measured in the surrounding soil. Average values of E between two irrigations when the crop was fully mature amounted f or 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 equatio n for the calculation of the reference evapotranspiration (ET(c)). A s tandard formulation was used for the resistance term, which might acco unt for the large value of K-c. Measurements of crop development param eters (height, leaf area index and phenological stage) showed some dif ferences between subplots during the growing period, but no final diff erences were detected. No differences in yield were observed during th e course of the study. Monitoring of physiological parameters (leaf wa ter potential, leaf conductance and net photosynthesis rate) showed th at water relationships of maize were not affected by the reduced N fer tilization.