Two field experiments were conducted in 2004 and 2005 seasons at El-Bosaily farm located at Beharia Governorate, Egypt, to study the effect of three nitrogen levels 60, 120 and 180 kg/feddan applied into irrigation water "fertigation" with drip irrigation system on vegetative growth, nutrient content (N, P and K) in leaves and grain and yield of three maize (Zea mays L.) hybrids (Single Cross 10, Three Way Cross 310 and Three Way Cross 324). The experiment design was a split plot with three replications where nitrogen fertilizer levels were distributed in the main plots and maize hybrids allocated in sub plots. The obtained results indicate that the increase of nitrogen level up to 180 kg /fed significantly increased plant height, number of leaves per plant, leaf area index, grain yield and straw weight. Single Cross 10 gave the significant highest vegetative growth and grain yield comparing with the other hybrids. The high-est nitrogen level (180 kg /fed) combined with Single Cross 10 gave the significantly highest grain yield and straw weight. On the other hand, 60 kg N / fed gave the highest nitrogen use effi-ciency (NUE) value followed by 120 kg N / fed The regression analysis of nutrition content (N, P, and K %) between leaf and grain was estimated. The highest regression determination coefficient (r2) was found in nitrogen percentage with r2= 0.965 followed by potassium with r2= 0.936. The lowest r2 was found in phosphorus with r2= 0.872.

Identification of specific physiological differences among maize genotypes (six inbred lines, four single crosses and four three-way crosses) to drought would be useful to plant breeders for improving selection criteria. Two field experiments were conducted in optimum and stress moisture conditions at Gemmeiza Agricultural Re-search Station in 2001 and 2003 growing seasons. The treatments were 14 geno-types, (six inbreds and eight hybrids), which were separately established under three irrigation treatments in split plot design with four replications. The genotypes were compared under water-deficit conditions on the basis of certain rapid techniques to determine leaf area index (LAI), photosynthetic efficiency (photo), canopy tempera-ture depression (CTD), stomatal conductance (SC) and chlorophyll (CHL) content which were deleteriously affected by water stress in the sensitive genotypes. Results revealed that values of LAI, photosynthetic efficiency, canopy temperature depres-sion, stomatal conductance and chlorophyll content of maize hybrids surpassed those of inbred lines. This was true at 30, 45 and 60 days after planting (DAP). Dif-ferences among maize hybrids and among inbred lines were significant at different growth stages for the same studied traits, except of the LAI for the inbreds, at 30 DAP and CTD for the hybrids at 30 as well as 60 DAP. Detecting certain physio-logical criteria, i.e. LAI, photosynthetic efficiency (photo), canopy temperature de-pression (CTD), stomatal conductance (SC) and chlorophyll content (Chl) could be used as reliable techniques to explore the physiological activity of maize genotypes at early stages of growth and may be recommended in screening different genotypes in maize breeding programs.