Effect of air‐drying on phosphorus fractions in clay soil |
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Authors: | Helena Soinne Mari Räty Helinä Hartikainen |
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Institution: | Department of Applied Chemistry and Microbiology, PL 27, 00014 University of Helsinki, Finland |
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Abstract: | Despite the publication of a number of papers dealing with the effect of drying on the soil labile P pool, less attention has been paid to the possible drying‐evoked changes in the more stable P pools. We applied Hedley's sequential fractionation procedure that aims at quantifying soil P reserves according to their decreasing plant availability to examine the effects of drying on soil P fractions in clayey soil samples of different cultivation history. To further investigate the contribution of organic matter disruption to the solubility of soil P, the P extracted in each fractionation step was divided into two size classes by filtering the suspension through a 0.2 μm membrane filter. There were no air‐drying‐induced changes in the total amount of P extracted in each fractionation step. However, air‐drying changed the distribution of water‐extractable P in size fractions; increase in the small‐sized P took place at the expense of large‐sized P. Air‐drying increased also small‐sized molybdate‐unreactive P (MUP) in the NaOH fraction giving evidence that drying‐induced alterations take place also in less labile P forms. The results revealed that air‐drying alters the extractability and distribution of P in various pools rather than the total amount of extracted P and that a large proportion of H2O‐ and NaOH‐extractable large‐sized MUP may remain undetected if only filtered samples are analyzed. |
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Keywords: | soil air‐drying filtering phosphorus fractionation |
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