CP Phase III Final Report 1991_Part 2.pdf - Lee Daniels - Soil and ...

o£ organic acids which complexed P-fixing elements in the spoil andreduced inorganic P fixation, althougb the same effect was not observed inthe sawdust plots.The three highest sludge rate treatments had the highest extractable Plevels over the course of the experiment, with extractable P generallyincreasing with sludge rate. A large amount of organic P was addedinitially as a component of the sludge and has apparently remained inavailable form over time, possibly as Ca-P and Fe-P complexes with organicmatter.Fescue Phosphorus Content and Phosphorus UptakeAlthough extractable soil P decreased over time, fescue P content inthe rock mix experiment actually increased with time (Table 21) .Thiscould indicate that the bicarbonate extraction used to measure P in thesemine soils was not a good indicator of the amount of plant-available soilP, or could have been caused by lower biomass production, making more Pavailable for uptake by each plant.Fescue P content in the rock mixexperiment dropped slightly in. 1983 and 1984, but increased in 1987.Highest P levels were measured in 1989 . Significantly higher t reatment Plevels were measured in the 1:1 sandstone mix in 1984 and 1987.Higheryields in the mixed spoil treatment may have created a larger pool oforganic P which was made available by litter decomposition . By 1989, therewas no significant difference in tissue P content between rock mixtreatments.During the first two years of the study, P uptake (Table 22) was50