Effect of CO2 on nitrification and immobilization of NH4+-N

A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO2 may be an important factor limiting nitrification. Soil samples amended with wheat straw (0%, 0.1% and 0.2%) and ((NH4)-N-15)(2)SO4 (200 mg N kg(-1) soil, 2.213 atom% N-15 excess) were incubated at 30 +/- 2 degreesC for 20 days with or without the arrangement for trapping CO2 resulting from the decomposition of organic matter. Nitrification ( as determined by the disappearance of NH4+ and accumulation of NO3-) was found to be highly sensitive to available CO2 decreasing significantly when CO2 was trapped in alkali solution and increasing substantially when the amount of CO2 in the soil atmosphere increased due to the decomposition of added wheat straw. The co-efficient of correlation between NH4+-N and NO3--N content of soil was highly significant (r = 0.99). During incubation, 0.1 - 78% of the applied NH4+ was recovered as NO3- at different incubation intervals. Amendment of soil with wheat straw significantly increased NH4+ immobilization. From 1.6% to 4.5% of the applied N was unaccounted for and was due to N losses. The results of the study suggest that decreased availability of CO2 will limit the process of nitrification during soil incubations involving trapping of CO2 (in closed vessels) or its removal from the stream of air passing over the incubated soil ( in open-ended systems).