Korean Journal of Soil Science and Fertilizer ISSN:0367-6315(Print) 2288-2162(Online) 한국토양비료학회 학회지

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.

A response of N balance to urea applications (0, 60, 120, and 180 kg N ha^-1) was linearly increased using Method A and C. However, the difference values of N balance between the method A and C in the combined N applications (Urea+CM 120 and 180 kg N ha^-1) were attributed to the change of soil N as considering independent factor for method C.