Abstract
This research documents the characteristic change of nitrogen in soil profile of a paddy field. Two soil columns (boxes) each comprising of four soil layers were constructed. Free air was introduced in one box and the effect of aerobic and anaerobic conditions was investigated. Soil profiles' performance was evaluated from a chemical (mass balance) perspective (T-N, NO2-N, NO3-N, NH4-N) coupled with a consideration of PO4-P and ORP when the columns were subjected to certain concentrations of KNO3 and KH2PO4 in the influent. The concentration of NO3-N decreased abruptly in upper layers and then exhibited a gradual recovery from 20 cm depth to the end of aeration zone under aerobic environment due to continued nitrification process, while its concentration was almost zero in anoxic condition beyond the same depth. NH4-N had appreciable concentration in the upper layers, and after that it became zero in aerated area. Contrary, it showed certain concentration in anaerobic condition. Such kind of tendency connotes the biochemical reactions of soil layers under the respective environments. T-N concentration demonstrated some diversity and it was considered that some nitrogen converted to gaseous products and emitted out as bubbles. ORP data explained well both the conditions, and water pressure distribution was also investigated. Consequently, the experiments showed comparable characteristic change of nitrogen, and displayed a greater ability for concrete recommendations.
