Effect of storage and sieving on the phosphorus composition of soil solution

In this study, the effects of storage and sieving of a mineral soil (Typic Fragiorthod) on the P chemistry of the soil solution have been quantified. Intact and sieved soil cores were stored for 0, 1, 3, and 8 d at 4 degrees C prior to obtaining solutions, which were analyzed for total dissolved phosphorus (TDP), molybdate-reactive phosphorus (MRP), dissolved organic phosphorus (DOP), and dissolved condensed phosphorus (DCP). Storage of both sieved and intact soil cores influenced the amount and chemical composition of P in solution. Concentrations of TDP, MRP, and DOP displayed a rapid decline with increase in storage time, whereas DCP concentrations, which were initially very low, increased. Concentrations of TDP were significantly (P < 0.05) different between solutions extracted from intact and sieved soils on the same day as sampling and this was accounted for by DOP and MRP, which were significantly (P < 0.05) larger in sieved soil. The proportions of MRP, DOP, and DCP were similar in solutions extracted from intact and sieved soils on the same day, even for Day 0 where a large difference in TDP was apparent. The MRP fraction was consistently larger for intact cores (44%) than sieved (38%) on all days and varied little with length of storage. The DOP component, which dominated initially, decreased with increase in storage time, while DCP increased to become the major fraction after 8 d of storage. This study has highlighted the potential effects of soil storage and sieving on the P concentration and composition of soil solution. The results also have important implications for soil solution sampling and subsequent data interpretation.