Figure 2. Reduction in leaf carbon exchange rate (CER) relative to leaf CER at high N as a function of weeks from silking for an older (‘Pride 5’) and a newer (‘NK N25-J7’) maize (Zea mays L.) hybrid exposed to (a) low N (LN), (b) HN switched to LN at 1 wk presilking (HLN₁), and (c) HN switched to LN at 2 wk postsilking (HLN₂). * Indicates when CER values were significantly lower (p < 0.05) under LN than under HN levels for each hybrid and moment of measurement.