Ammonia Emission from Soybean-Amended Calcareous Soil with Various Soil Temperature and Moisture Levels
1992
O'Deen, W. A. | Follett, R. F.
High soil temperature, moisture, and crop residue levels were found to combine for maximum volatilization of ammonia from calcareous soil amended with soybean [Glycine max (L.) Men.] tissue in this study. An unusually large amount of ammonia was liberated to the atmosphere and provided the opportunity to measure accurately isotope separation of ¹⁵N and ¹⁴N atoms resulting from the diffusion process. Soybean tissue (early reproductive stage) was mixed with a calcareous soil (Aridic Paleustoll) at two different levels (25 and 50 g kg⁻¹). The two soil soybean-tissue mixtures were wetted to the desired moisture content (20, 60, and 100% field capacity) and incubated 7 d at either 10,20, or 30 °C. After incubation, ammonia evolution and moisture loss were determined during either a 4- or 7-d dry-down period in which dry NH₃-free air was passed across the soil surface. We found more NH₃ volatilized at 1Wo FC than at 20 or WO FC, at 30 than at 10 or 20 °C, and at 50 than at 25 g kg⁻¹ residue rate. Maximum loss of NH³ was about 5% of soybean-tissue N measured in an experiment in which four wet-dry cycles were used. Maximum loss was directly related to water evaporation rate. These results indicate that soil temperature, moisture, and crop-residue rates all influence NH₃ losses from soybean-tissue amended soil. Isotopic ratios of the NH³−N evolved were measured and ammonia content of the first fraction of ammonia volatilized was lower in atom YO ¹⁵N than the last fraction. These results indicate that, for the conditions of this study, diffusion is an important process since the ¹⁴N atoms volatilized more quickly as NH³ than did the ¹⁵N atoms. Contributions from the USDA.
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