| Abstrakt: |
Available soil P (AP) is usually based on inorganic P (Pi) soil‐test levels, a practice that ignores the potential contribution of organic P (Po) mineralization. Our objective was to develop a P‐availability index that included both Piand Podymanics. Fourteen Kansas soils, ranging in bicarbonate‐extractable Pifrom 1.5 to 21.5 mg P kg−1, were used. One set of soils was untreated and another enriched with C + N source to raise microbial activities and create a biological sink for P. The treated soil was designated as bioactive. After 7 d of incubation, we measured the quantity of NaHCO3‐extractable Pi, total P (Pt), and inorganic plus microbial P (Pi+m) in both soils and used these data to describe the size of the labile Po, microbial P (Pm), immobilized Pi(Pimmob), potentially mineralizable Po(Pmin), total bioavailable P, and bioavailable Popools. Bioactive soils always had less Pithan untreated soils after incubation, probably, because of microbial immobilization. Labile Poin the bioactive soils averaged 2.4 times greater than in untreated soils. Labile Poafter incubation averaged 2.8 times greater than the Pilevel prior to incubation in bioactive soils and remained essentially the same in untreated soils. Clearly, microbial activity enhanced Poavailability, an increase in AP that would not be apparent in soil tests where chemical extractions measure only Pi. We combined the Pi, Po, and Pmpools to create a bioavailable‐P index. This index differed from the typical soil‐test P index (preincubation Pi) more for the bioactive soil (r2= 0.50) than for the untreated soil (r2= 0.74). These data suggest this extraction scheme can enhance understanding of the P‐supplying power and P nutritional dynamics of certain soils. |
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