Mechanism of the Formation of Exchangeable Ammonium Nitrogen Immediately after Waterlogging of Rice Soils

When several rice soils (West Bengal) were waterlogged for 10 days, a marked increase of exchangeable ammonium nitrogen in many soils was observed, while in some of the soils it remained more or less same Simultaneously the fixed ammonium nitrogen of the soil decreased in the previous case but it remained stationary in the latter case. The aforesaid observations strongly suggest that in waterlogging of rice soils there was an expansion of crystal lattices of clay minerals (depending on the nature of mineralogical composition) when a part of the fixed NH₄-N came out and were held as an exchangeable complex outside the crystal lattice. That the increase of exchangeable NH₄-N during this short period of waterlogging was not due to microbial activities was proved by another experiment in which the temperature was raised to 60°C for three days.