The relative flow 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 shortand 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 CI‐I accumulation and less Nred remobilization from the leaf and stem. Sink‐limited treatments had greater postanthesis N absorption and grain N concentration than the sourcelimited treatments. As the source/sink ratio decreased, N flow to the grain per unit of C flow 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.
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Uhart et al. (1995) studied this question.