A field experiment was conducted to investigate the carbon (C) and nitrogen (N) balance in relation to grain formation and leaf senescence in two different senescent types of maize (Zea mays L.), one stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55). In comparison with Hokkou 55, P3845 had a higher N concentration (Nc) in the leaves and a higher specific N absorption rate by roots (SARN), which indicated that a large amount of N was supplied to the leaves from the roots during maturation. This resulted in a higher photosynthetic rate, which supports saccharide distribution to roots. Thus, stay-green plants maintained a more balanced C and N metabolism between shoots and roots. Moreover, the coefficients of the relationship between the relative growth rate (RGR) and Nc, and between the photon-saturated photo-synthetic rate (Psat) and Nc were lower in P3845. The Psat per unit Nc in leaves was lower in the stay-green cultivars, which indicated that high yield was attained by longer green area duration and not by a high Psat per unit Nc in the leaf. Consequently, a high Psat caused a high leaf senescence rate because C and N compounds will translocate actively from the leaves. and Ping He ... [et al.].