Assessing soil nitrous oxide emission as affected by phosphorus and nitrogen addition under two moisture levels

Agricultural soils are deficient of phosphorus (P) worldwide. Phosphatic fertilizers are therefore applied to agricultural soils to improve the fertility and to increase the crop yield. However, the effect of phosphorus application on soil N2O emissions has rarely been studied. Therefore, we conducted a laboratory study to investigate the effects P addition on soil N2O emissions from P deficient alluvial soil under two levels of nitrogen (N) fertilizer and soil moisture. Treatments were arranged as follows: P (0 and 20 mg P kg(-1)) was applied to soil under two moisture levels of 60 and 90% water filled pore space (WFPS). Each P and moisture treatment was further treated with two levels of N fertilizer (0 and 200 mg N kg(-1) as urea). Soil variables including mineral nitrogen (NH4+-N and NO3--N), available P, dissolved organic carbon (DOC), and soil N2O emissions were measured throughout the study period of 50 days. Results showed that addition of P increased N2O emissions either under 60% WFPS or 90% WFPS conditions. Higher N2O emissions were observed under 90% WFPS when compared to 60% WFPS. Application of N fertilizer also enhanced N2O emissions and the highest emissions were 141 mu g N2O kg(-1) h(-1) in P+N treatment under 90% WFPS. The results of the present study suggest that P application markedly increases soil N2O emissions under both low and high soil moisture levels, and either with or without N fertilizer application.