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 so urce/sink ratio of the crop. The objective of this work was to analyze the C and N accumulation and remobilization patterns of maize (Zea ma ys L.) under a wide range of source/sink ratios, The experiment was co nducted at Balcarce, Argentina, during 2 yr with both a short- and lon g-season hybrid. The treatments consisted of two levels of source redu ction (45 and 55% shading during the grain filling period), two levels of reproductive sink reduction (45 and 55% shading during a 30-d peri od bracketing silking), and an unshaded control. The shading treatment s had a variable duration (30-38 d) to ensure constant incident radiat ion. 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 s tem CH accumulation and less Nred remobilization from the leaf and ste m. Sink-limited treatments had greater postanthesis N absorption and g rain 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 increasi ng source limitation. Linear quantitative relationships between source /sink ratio and CH remobilization, N remobilization, relative C-N flux es to the kernel, and kernel N concentrations have been established.