EVALUATION OF THE DIFFERENT N-SENSITIVITY OF 2 MODEL HYBRIDS FOR MAIZE

Exploitation of sensitivity to N-supply of maize (Zea mays L.) genotyp es is of both economical and environmental importance. Therefore, the objectives of this study were to identify the N-sensitivity of differe nt maize genotypes, and to find the possible explanations for this sen sitivity: Two-model hybrids were investigated in a 2-yr lysimeter tria l, where low, moderate, and high N-supplies (50:50% ammonium and nitra te) were provided. This resulted in extra low, low, medium, and high y ield levels in the two years investigated. Supply of water was control led. One hybrid was considered as N-sensitive, whereas the other was c onsidered as N-tolerant according to their performance in earlier eval uations. In the present study, N-sensitivity was determined regarding the N-response of whole plant, grain, and N yields of the two hybrids. The N-sensitive genotype proved to be sensitive at either low or high N-supply showing yield increases, and decreases, respectively, compar ed with the N-tolerant hybrid, while the latter produced higher yields at the medium N-treatment. The higher N-sensitivity might be due to t he lower N-uptake, within which a higher NH4+-N ratio could result in less energy requirement for N-assimilation; or lower N-storage capacit y; or better N-efficiency. However, the N-tolerant took up more NO3--N from the soil, therefore it was effective to decrease NO3--N leaching . Regarding to the differences between the two genotypes in storage ca pacity and efficiency, the N-sensitive genotype seems to be more suita ble for grain production, while the tolerant one for forage use. Furth er research should focus on morphological and biochemical reasons of h ybrid differences in N-uptake, N-efficiency, and storage capacity.