nitrogen transformations in cropland

We considered of N transformation processes among the three soil N pools (organic N, NH₄⁺, and NO₃⁻), namely gross N mineralization (oxidation of organic N to NH₄⁺), gross heterotrophic nitrification (oxidation of organic N to NO₃⁻), gross autotrophic nitrification (oxidation of NH₄⁺ to NO₃⁻), gross dissimilatory NO₃⁻ reduction to NH₄⁺ (DNRA), gross NH₄⁺ immobilization (the conversion of NH₄⁺ to organic N), and gross NO₃⁻ immobilization (the conversion of NO₃⁻ to organic N). Additionally, we took into account plant NH₄⁺ uptake<i> </i>(<i>U</i>_NH4) and plant NO₃⁻ uptake (<i>U</i>_NO3). Observations (upland/paddy) include N mineralization (334/114), autotrophic nitrification (199/109), heterotrophic nitrification (161/98), NH₄⁺ immobilization (210/113), NO₃⁻ immobilization (194/23), DNRA (150/111), <i>U</i>_NH4 (76/38), <i>U</i>_NO3 (76/38). The <i>U</i>_N (76/38) was also calculated as the sum of <i>U</i>_NH4 and <i>U</i>_NO3.