Using an Ion Sink to Extract Microbial Phosphorus from Soil

Abstract

Two ion sinks (FeO‐coated paper and anion exchange resin membrane) were tested to improve accuracy and precision in analysis of microbial P (Pm) in soil biomass. We used a noncarcinogenic biocide, hexanol. Ion‐sink extracted FeO‐Pm [Pm(FeO)] and resin‐Pm [Pm(Res)] were compared with bicarbonate extracted Pm [Pm(Bic)]. Fractional recovery of Pm (Kp) was determined with 50 μg Pm from five different organisms, first, from preparations without soil, giving Kp of 0.49 for Pm(Bic), 0.63 for Pm(FeO), and 0.66 for Pm(Res), and second, from soil‐organism mixes, giving Kp of 0.36 for Pm(Bic), 0.49 for Pm(FeO), and 0.52 for Pm(Res) This indicated ion sinks can improve accuracy of Pm recovery. We tested 18 Kansas soils with three different levels of C + N substrates to provide varying levels of microbial activity. For unamended soils, Pm values (mg kg−1) were 5.9 for Pm(Bic), 8.2 for Pm(FeO), and 6.3 for Pm(Res) Corresponding values in soils with low levels of C + N amendments were 6.0 for Pm(Bic), 18.2 for Pm(FeO), and 18.7 for Pm(Res) In soils with high levels of C + N amendments plus alfalfa (Medicago sativa L.), corresponding values were 12.7 for Pm(Bic), 30.9 for Pm(FeO), and 37.3 for Pm(Res) Above 10.0 mg kg−1, Pm(FeO) and Pm(Res) were at least twice as much as Pm(Bic) In addition, Pm(FeO) and Pm(Res) both had lower CVs than Pm(Bic), indicating greater precision by the ion‐sink methods.