In Situ Transformations of Nitrogen-15 Labeled Materials in Sonoran Desert Soils1
- R. L. Westerman and
- T. C. Tucker2
Influences of ammonium, nitrate, organic N sources and organic C amendments on microbial respiration, N transformations and gaseous losses were measured under natural environmental conditions in two field experiments. Microbial respiration was increased by addition of wheat straw and barley grain. Addition of N as (15NH4)2SO4 and K15NO3 alone did not increase CO2 evolution significantly.
Significant immobilization of added inorganic-15N occurred with few exceptions in all treatments except nitrate alone. Organic-15N in soils amended with wheat straw increased with increasing N rates with both inorganic N sources. Inorganic-15N was practically void in both soils at the end of 12 months. Mineralization of 15N-labeled barley grain occurred but at a very low rate and no significant accumulations of inorganic-15N were observed.
Gaseous losses of N at the end of 12 months varied from 73 to 94% of the inorganic-N added alone, with the greatest loss occurring from K15NO3. The incorporation of wheat straw stimulated immobilization of added N and reduced gaseous losses to 30 to 86% of the total N applied and the smallest loss occurred with (15NH4)2SO4. The average loss of mineralized organic-15N derived from barley grain for the two soils was 19% of the total N added. Most of the gaseous losses occurred within the first 3 months, the period of the measurable rainfall.
Analyses of subdivided soil sections (0–5 and 5–10 cm) showed that 95 to 100% of 15N remaining in the soil was in the upper 5-cm layer indicating that leaching was not appreciable in any treatment.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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