Soils which have been saturated with water for a prolonged period of time may show an increased soil test pH value. The main reason for the change is the denitrification of soil nitrate to nitrogen gas which occurs under anaerobic conditons. For each atom of nitrate nitrogen which is converted to nitrogen gas, 6 atoms of acidic hydrogen are neutralized by forming water molecules as part of the bio-chemical reaction. The amount of pH change is dependent on the amount of residual nitrates in the soil and may increase as much as several tenths of a pH unit. Since this change in soil pH is due to a non-reversible bio-chemical reaction, we suggest that farmers follow the soil test lime recommendations from samples collected from these flooded soils and make no adjustments to the recommended lime application rate.
