Short-Term Sucrose Feeding Fails to Increase Yield of Maize.

Nitrogen (N) limitation reduces leaf growth and photosynthetic rates of maize (Zea mays L.), and constrains photosynthate translocation to developing ears.  Additionally, the period from about one week before to two weeks after silking is critical for establishing the reproductive sink capacity necessary to attain maximum yield.  To investigate the influence of carbohydrate availability in plants of differing N status, a greenhouse study was performed in which exogenous sucrose (suc) was infused around the time of silking into maize stems grown under different N regimes.  Nitrogen deficiency significantly reduced leaf area, leaf longevity, leaf chlorophyll content and photosynthetic rate.  High N delayed leaf senescence, particularly of the six uppermost leaves, compared to the other two N treatments.  While N application increased ear leaf soluble protein concentration, it did not influence glucose and suc concentrations.  Interestingly, ear leaf starch concentration decreased with increasing N application.  Infusion of exogenous suc tended to increased nonstructural carbohydrate concentrations in the developing ears of all N treatments at silking and six days after silking (DAS).  However, leaf photosynthetic rates were not affected by suc infusion, and suc infusion failed to increase grain yield in any N treatment.  The lack of an effect of suc infusion on ear growth and the high ear leaf starch concentration of N deficient maize, suggest that yield reduction under N deficiency may not be due to insufficient photosynthate availability to the developing ear during silking, and that yield reduction under N deficiency may be determined at an earlier growth stage.