Submitted to: American Society of Agronomy Meetings
Publication Type: Abstract Only
Publication Acceptance Date: November 4, 1999
Publication Date: N/A
Technical Abstract: **15N fertilizer studies have shown that organic N is the major source of N for plant growth. Many N mineralization tests have been proposed to measure soil N release, but studies have found poor correlations between net N released and crop yields. This study compared aerobic and anaerobic tests (1-4 wk, 30 degrees C) and long-term leaching (26 wk, 20 degrees C) N mineralization tests with oat and ryegrass uptake studies (26 wk, 20 degrees C) as measures of N release in six Iowa soils. Correlation values for plant N uptake and N mineralization tests were different for each plant species and the N mineralization tests were not significantly correlated. Most soils showed low net N release with 2 or 4 wk incubations and soils increased in amino acid-N content with incubation suggesting that C and N microbial interactions determined N release. Since no plant residue was added with the soil incubations, the low N mineralization and immobilization of mineral N present before incubation emphasizes the delicate balance between uptake by soil microorganisms and short term N release. The results question the use of N mineralization for predicting N needs as a means of reducing N inputs.