ISHS Acta Horticulturae 448: III International Symposium on Mineral Nutrition of Deciduous Fruit Trees
EFFECTS OF THE NITROGEN-FERTILISER FORM ON RHIZOSPHERE PH AND GROWTH OF APPLE IN SOILS WITH DIFFERENT BUFFER CAPACITY |
| Authors: | M. Tagliavini, D. Neilsen, E.J. Hogue, G.H. Neilsen |
| Keywords: | apple, manganese toxicity, nitrogen nutrition, rhizosphere pH, soil acidification |
| Abstract:
Soils may differ in their ability to counteract root induced pH changes, according to their proton buffer capacity. In the present study we tested the hypothesis that the N form (NO3- or NH4+) affects the pH of root/soil interface depending on soil buffer capacity. Rooted M.9 apple rootstocks were grown in 5 L pots filled with either a poorly buffered, loamy sand soil (pH=6.7 in CaCl2; buffer capacity= 1.29 cmol kg-1) or a well buffered, silt-loam soil (pH=7.1; buffer capacity= 4.43 cmol kg-1) collected from the A horizon of two orchards located in Interior British Columbia (Canada). The young trees were grown in a greenhouse and regularly fertigated for 40 days with ammonium sulphate or calcium nitrate (4mM) for a total of 414 mg N/pot. Shoot and root growth was depressed by the ammonium-type fertiliser. Rhizosphere pH, measured by colour changes of an agar/bromocresol film placed on selected roots, was unaffected by the fertiliser type in the silt loam soil, while in the loamy sand one, it averaged 4.7 or 5.6 following NH4 or NO3 nutrition, respectively. The strongest acidification at root level was found in the silt loam soil, in spite of its higher buffer capacity. The ammonium type fertiliser depressed bulk soil pH and enhanced Mn leaf concentration to levels considered toxic to apple, while that of Ca(NO3)2 increased leaf Ca concentration. Results indicate that the addition of ammonium-type fertilisers may develop acidification both at soil and rhizosphere level; their use should therefore be carefully considered in low buffered and acid soils. We speculate that in addition to N form and soil buffer capacity, other factors such as cation/anion ratio may regulate the pH at the root/soil interface. | |
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