In short-term water culture experiments with different 15N labeled ammonium or nitrate concen trations, citrus seedlings absorbed NH; at a higher rate than No;. Maximum NO; uptake by the whole plant occurred at 120 mg L – 1 NO;-N, whereas NH; absorption was saturated at 240 mg L – 1 NH;-N. 15NH; accumulated in roots and to a lesser degree in both leaves and stems. However, 15NO; was mostly partitioned between leaves and roots.
Adding increasing amounts of unlabeled NH; (15-60 mg L – 1N) to nutrient solutions containing 120 mg L -1 N as 15N labeled nitrate reduced 15NO; uptake. Maximum inhibition of 15NO uptake was about 55% at 2.14 mM NH; (30 mg L – 1 NH;-N) and it did not increase any further at higher NH; proportions. In a long-term experiment, the effects of concentration and source of added N (NO; or NH;) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH; versus NO; nutrition, whereas the reverse was true for Ca, K, Zn and Mn.
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Source:
M. D. Serna, R. Borras, F. Legaz and E. Primo-Millo
Instituto Valenciano de Investigaciones Agrarias, Spain