| Summary: | The purpose with this report was to compare three commonly occurring methods for measuring plant available nitrogen in soils. The methods extraction, incubation and Plant root simulator (PRS) probe - an ion exchange membrane (Western Ag Innovations, Inc., Saskatoon, Canada) method were used and comparison between these methods were conducted. A full factorial experiment were set up in northern Finland with the treatments excluding herbivores, warming and fertilization to see how the inorganic nitrogen content in the soil was effected by the treatments. Soil cores were taken and from them a subsample was incubated for 18 days and thereafter analyzed for inorganic N in laboratory. PRS- probes were in the ground for 1 month. It was a strong positive correlation between extracted and incubated samples but no correlation between the PRS- probes and extraction or incubation samples. The PRS- probes showed several significant changes in inorganic N content after the treatments where fertilization increased the tot-N and NO3 levels and warming reduced the inorganic tot-N, NH4 and NO3. These findings were not confirmed by the results of the extraction. The incubation showed negative net mineralization rates for tot- N and NH4. PRS- probes showed a slightly dominance of NO3 over NH4 while extraction showed a many times higher amount of NH4 compared to NO3. Extraction shows a strong correlation with incubation even though extraction measure an instantaneous value and incubation measure the production of inorganic nitrogen over time.
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