| Abstrakt: |
Maize (Zea maysL.) has a noted propensity for accumulating large amounts of nitrate‐N (NO3‐N). However, the availability of such NO3‐N for assimilation during periods of restricted N supply has not been assessed. In addition, the availability of sulfate‐S (SO4‐S) affects the accumulation and assimilation of NO3‐N. Little is known about the effect of NO3‐N supply on SO4‐S accumulation. Such information is vital to efforts to improve the efficiency of nutrient utilization by crops. The objective of this greenhouse experiment was to determine the effect of N deprivation during grain‐filling on the accumulation of dry matter, NO3‐N, and SO4‐S. Maize plants were grown hydroponically in a modified Hoagland's solution. At silking the nutrient solution was replaced with fresh solution, with or without NO3‐N. Plants were harvested and separated into seven fractions at silking and 1, 2, 3, 5, and 7 weeks after silking. Plants that were supplied NO3‐N during grain‐filling contained almost twice (1.8×) as much N at physiological maturity (7 weeks after silking) as did N‐deprived plants. Ear dry weight was not affected by N deprivation. The concentration of NO3‐N in all fractions declined during grain‐filling; however, N deprivation enhanced this decline in the roots, lower stem, and upper stem. Lack of N did not affect NO3‐N concentration in the lower leaves, upper leaves, or ear. The concentration of SO4‐S in the roots nearly doubled between silking and physiological maturity when plants were deprived of NO3‐N, but did not change when N was supplied. The concentration of SO4‐S in all other parts was not markedly affected by N deprivation. Apparently, maize plants can compensate for a restricted N supply during grain‐filling by utilizing NO3‐N stored in the roots and stem. |
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