Root growth as a function of ammonium and nitrate in the root zone |
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Authors: | A J BLOOM L E JACKSON D R SMART |
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Institution: | Department of Vegetable Crops, University of California, Davis, CA 95616, USA |
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Abstract: | We examined the effect of soil NH4+ and NO3? content upon the root systems of field-grown tomatoes, and the influence of constant, low concentrations of NH4+ or NO3? upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH4+ or NO3?; they increased to a maximum in zones having 2μg-N NO3? g?1 soil and 6 μg-N NO3= g?1 soil, but decreased in zones having higher NH4+ or NO3? levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH4+ or NO3?, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO3?. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH4+ and NO3?. |
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Keywords: | Lycopersicon esculentum Solanaceae tomato roots root growth soil nitrogen acid-growth ammonium nitrate |
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