Comparison of Different Approaches on Determining Nitrogen Balance in a Lowland Paddy Soil

Nitrogen (N) balance is a key indicator assessing a degree of soil fertility and N loading by accounting input minus output N in agro-ecosystem. However, a recent approach on determining N balance has been evaluated regarding a change in soil N stock for continuing crop cultivation. To describe an assessment method on N balance, this study was conducted with three different methods, Method A (Input N−Output N (crop N removal+Loss N) = N surplus or deficit), Method B (Input N − Output N (crop N removal+Loss N + Δ soil total N) = N surplus or deficit), and Method C (Input N − Output N (crop N removal+Loss N) + Δ soil total N = N surplus or deficit). Four levels (0, 60, 120, and 180 kg N ha-1) of N from urea and two levels (120 and 180 kg ha-1) of N from combination of urea and CM (Urea:Cattle Manure = 60:60 and 60:120) were applied in a lowland paddy soil. Results showed that Method B indicated all negative N values regardless the sources and rates of N application, while Method A and C described different N balance values in the given N applications. Using Method A, a response of N balance to urea applications (0, 60, 120, and 180 kg N ha-1) was linearly increased. The values of N balance were negative at 0 and 60 kg N ha-1, while it was close to zero at 120 kg N ha-1 and showed the higher value at 180 kg N ha-1, respectively. Similarly, the combined N applications at 120 and 180 kg N ha-1 showed similar N balance values. Meanwhile, Method C indicated different N balance values at the combined N applications, showing significantly higher N balance values at 120 kg N ha-1 and the more value at 180 kg N ha-1, as compared with Method A. The difference was attributed to the soil N stock considering as count factor in determination of N balance. Thus, the study recommended Method C when evaluating both of soil fertility and N loading in crop cultivation field. KCI Citation Count: 1