Kalkningens påverkan på fosforlöslighet
skakförsök baserade på två svenska långliggande kalk- och fosforgödslingsförsök
Eutrophication is an environmental problem that affects more than ten percent of Swedish lakes. Excess nutrients increase the growth of algae, and cause major problems in the ecosystem through oxygen-free bottoms, fish kills, and at worst dead bottoms. Agriculture accounts for 44% of human emissions of phosphorus to lakes and rivers. Leaching occurs of particle bound phosphorus and of dissolved
phosphate. The amount of phosphate in the soil solution that may be leached is partly due to the prevailing pH in the soil solution.
The purpose of this study was to investigate how the relationship between phosphate solubility and pH was affected by liming. A second objective was to estimate the liming effect on potential leaching of dissolved phosphate from the soil. A laboratory study was conducted that was based on soil samples from two Swedish long-term field experiments, the experimental stations of Lanna and
Röbäcksdalen. A batch leaching was performed where the soil pH was adjusted using acid and base. The resulting pH and the concentrations of dissolved phosphorus, calcium, aluminum and iron were then measured.
The results showed that the solubility of phosphorus increased when liming had been combined with fertilization in the field experiments. In soil samples from Lanna phosphate solubility increased at any pH in the studied pH range when lime was added in combination with fertilization. Since the solubility of phosphorus was
increased by liming at a given pH, it was not the pH increase itself that caused the increased solubility. This suggests that applied fertilizer phosphorus is bound and
released by a different mechanism if liming is simultaneously taking place. In soil samples from Röbäcksdalen no significant difference in phosphate solubility due to liming could be proved. This may indicate that it is difficult to draw general conclusions about the effect of liming on phosphorus solubility.
The potential leaching from fertilized experimental plots increased when lime had been added, whereas no significant liming effect was detected in unfertilized plots. Also in this case, it seems to be some effect of the liming other than the pH-change itself, that increases the phosphorus solubility.
This study is a part of an ongoing research project in the field.