| Summary: | Abstract Ammonia (NH3) volatilization loss adversely affects N availability in soil‐plant systems, reduces crop yield, and negatively impacts environment. Char (coal combustion residue), which contains up to 293 g kg−1 total C by weight, has been shown to reduce NH3 volatilization due to its considerably high surface area and cation exchange capacity. The NH3 loss can be greatly affected by a shift in soil pH or urea hydrolysis. A 21‐d laboratory study was conducted to evaluate the effects of char on soil pH, N transformations, and subsequent NH3 volatilization in sandy loam soil. Two char rates (0 and 13.4 Mg C ha−1) and two urea rates (0 and 200 kg N ha−1) were mixed in soil in four 2‐way combinations with four replications of each. There were 11 sets of all treatment combinations and each set was analyzed for soil moisture, pH, NH3 volatilization, and residual N (urea, NH4, and NO3) every other day for 3 wk. Char application reduced cumulative NH3 loss in the fertilized treatment. Reduction in NH3 loss due to char addition was evidenced by greater residual NH4–N on certain days in treatments with char compared to treatments without char. Char did not affect urea hydrolysis process but it lowered soil pH in the fertilized treatments in the first week. This study supported our hypothesis that char altered soil pH and thereby reduced NH3 volatilization loss from the fertilized soil.
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