Changes in 15N abundance and amounts of biologically active soil nitrogen
1999
Liang, B.C. | Mackenzie, A.F. | Gregorich, E.G.
Estimation of the capacity of soils to supply N for crop growth requires estimates of the complex interactions among organic and inorganic N components as a function of soil properties. Identification and measurement of active soil N forms could help to quantify estimates of N supply to crops. Isotopic dilution during incubation of soils with added 15NH4+ compounds could identify active N components. Dilution of 15N in KCl extracts of mineral and total N, non-exchangeable NH4+, and N in K2SO4 extracts of fumigated and nonfumigated soil was measured during 7-week incubation. Samples from four soils varying in clay content from 60 to 710 g kg-1 were used. A constant level of 15N enrichment within KCl and K2SO4 extracted components was found at the end of the incubation period. Total N, microbial biomass C and non-exchangeable NH4+ contents of the soils were positively related to the clay contents. The mineralized N was positively related to the silt plus clay contents. The active soil N (ASN) contained 28-36% mineral N, 29-44% microbial biomass N, 0.3-5% non-exchangeable NH4+ with approximately one third of the ASN unidentified. Assuming that absolute amounts of active N are related to N availability, increasing clay content was related to increased N reserve for crop production but a slower turnover.
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