NITROGEN AND CARBON ACCUMULATION AND REMOBILIZATION DURING GRAIN FILLING IN MAIZE UNDER DIFFERENT SOURCE/SINK RATIOS

The relative Bow and remobilization of carbon (C) and nitrogen (N) to the grain during the grain filling period depends on the particular source/sink ratio of the crop. The objective of this work was to analyze the C and N accumulation and remobilization patterns of maize (Zea mays L.) under a wide range of source/sink ratios, The experiment was conducted at Balcarce, Argentina, during 2 yr with both a short- and long-season hybrid. The treatments consisted of two levels of source reduction (45 and 55% shading during the grain filling period), two levels of reproductive sink reduction (45 and 55% shading during a 30-d period bracketing silking), and an unshaded control. The shading treatments had a variable duration (30-38 d) to ensure constant incident radiation. The source limitation produced increases in remobilization rates of leaf + stem reduced N (Nred) and stem nonstructural carbohydrates (CH) compared with the control. The sink limitation generated greater stem CH accumulation and less Nred remobilization from the leaf and stem. Sink-limited treatments had greater postanthesis N absorption and grain N concentration than the source-limited treatments. As the source/sink ratio decreased, N flow to the grain per unit of C Bow decreased suggesting that N becomes more limiting for grain yield with increasing source limitation. Linear quantitative relationships between source/sink ratio and CH remobilization, N remobilization, relative C-N fluxes to the kernel, and kernel N concentrations have been established.