Soo-Myung Choi

Nitrogen transformations and ammonia volatilization losses from 15N-urea as affected by the co-application of composted pig manure

Co-application of composted manure (compost) and urea is considered an environment-friendly fertilization practice; however, the high urease activity in compost may stimulate NH3 volatilization and cause N loss from co-applied urea. To test the above hypothesis, we investigated the fate of urea co-applied with compost in a loam-textured soil through two laboratory incubation experiments. Urea (150 mg N kg-1) was co-applied with 0, 4.9, 9.8, and 14.6 g of compost (oven-dry basis) kg-1 of soil, designated as treatments UC0, UC1, UC2, and UC3, respectively. Co-application of compost and urea enhanced urea hydrolysis and increased the 1st order rate constant of urea hydrolysis from 0.047 h-1 in the UC0 to 0.139 h-1 in the UC3 treatments. Soil pH increased from 7.0 for UC0 to 7.6 for UC3, leading to greater NH3 volatilization (up to two times more) in the soils receiving 9.8 g kg-1 or more of compost. Compost co-application also increased the immobilization of urea-derived N, probably because the organic matte...

Nitrogen Inputs with Different Substrate Quality Modified pH, Eh, and N Dynamics of a Paddy Soil Incubated under Waterlogged Conditions

Synthetic fertilizer, livestock manure, and green manure are the typical nitrogen (N) sources in agriculture. This study was conducted to investigate the effects of different N sources on soil chemical environment and N dynamics. Changes in pH, redox potential (Eh), and concentration and δ15N of dissolved N [ammonium (NH4+), nitrate (NO3−), organic N, and total N] of soils treated with urea (U), pig manure compost (PMC), and hairy vetch (HV) were investigated in an incubation experiment under waterlogged conditions. The patterns of pH, Eh, and N concentration reflected both a greater mineralization potential of N derived from U than that from HV and PMC and easier decomposability of HV than PMC. The δ15N further suggested that nitrification was more active for U than for HV- and PMC-treated soils and that N loss via NH3 volatilization and denitrification would be greater for HV than U and PMC treatments.