| Sumario: | In soils with relatively high pH (pH > 7), potatoes (Solanum tuberosum L.) and other
phosphorus (P) demanding crops might suffer from P deficiency despite P fertilization and
significant reserves of P in the soil. Also, a high risk for P deficiency for potatoes may be
expected when the soil is cold and the root system undeveloped. Therefore, the risk of Plimitation
in high-pH soils is probably greatest for early varieties. In this study a trial was set
up with two objectives: (i) To assess the effect of ammonium sulphate (T1) on P uptake,
vegetative growth and tuber yield in potatoes grown without addition of P in soils with
relatively high pH (7.5) and P-AL class IVB (12.5 mg P/100 g soil), under climatic conditions
similar to those for early potatoes in the south of Sweden. The effect of ammonium sulphate
was compared with the effect of ammonium nitrate (T2), ammonium chloride (T3) and
potassium nitrate (T4). (ii) To assess the impact of inoculation with spores of arbuscular
mycorrhizal fungi (AMF) Rhizophagus irregularis (T5) and the phosphorus solubilizing
bacteria (PSB) Bacillus megaterium (T6) on the said parameters and under the same
conditions. The trial was limited to the early potato variety ‘Solist’ grown with one level of
nitrogen fertilizer. After harvesting, data was collected on fresh and dry matter and shoots and
tubers were analysed for P content. The potato plants in the trial did not reach full maturity,
probably due to salt toxicity, which made any possible differences between the treatments
difficult to discern. At harvest the P concentration in all plants in all treatments was lower
than normal levels. No significant differences were found between treatments on the effect on
total dry weight of tubers or shoots. Also, no significant differences were found between
treatments in number of tubers produced. The plants which received ammonium chloride (T3)
had a significant smaller concentration of P compared to T1, T2 and T5. The difference can
probably be explained by the fact that T3 had the highest salt concentration of all treatments.
AMF colonization in the roots were found in all pots in both the control T2 and the inoculated
T5. In conclusion, the result did not support the hypothesis that it would be possible to control
P availability for early potatoes, grown in alkaline soils with relatively high P content,
through the choice of nitrogen source or through inoculation with PSB or AMF.
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