ISSN:
1573-5036
Keywords:
ammonium
;
citrus
;
nitrate
;
NO3 −/NH4 + ratio
;
nitrogen
;
nutrient solution
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract In short-term water culture experiments with different 15N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH4 + at a higher rate than NO3 −. Maximum NO3 − uptake by the whole plant occurred at 120 mg L−1 NO3 −-N, whereas NH4 + absorption was saturated at 240 mg L−1 NH4 +-N. 15NH4 + accumulated in roots and to a lesser degree in both leaves and stems. However, 15NO3 − was mostly partitioned between leaves and roots. Adding increasing amounts of unlabeled NH4 + (15–60 mg L−1 N) to nutrient solutions containing 120 mg L−1 N as 15N labeled nitrate reduced 15NO3 − uptake. Maximum inhibition of 15NO3 − uptake was about 55% at 2.14 mM NH4 + (30 mg L−1 NH4 +-N) and it did not increase any further at higher NH4 + proportions. In a long-term experiment, the effects of concentration and source of added N (NO3 − or NH4 +) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH4 + versus NO3 − nutrition, whereas the reverse was true for Ca, K, Zn and Mn. The effects of different NO3 −-N:NH4 +-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L−1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO3 − or NH4 + as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO3 −-N/NH4 +-N ratio. With increasing proportions of NH4 + in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH4 +, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO3 −-N:NH4 +-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH4 + in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO3 −:NH4 + ratio.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00009366
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