(NoTE: TCMP is the preferred nitrification inhibitor but requires handling and transfer in a solid form. Allylthiourea is not always effective in inhibiting nitrification within the 5-d incubation period and con centrations above 2 mg/L may cause increases in carbonaceous BOD measurements. ATU concentrations above 2 mg/L also can adversely affect the azide modification of the iodometric method). Seed all samples to which nitrification inhibitor has been added. The amount of seed should be consistent with that re- quired to achieve GGA test results in the range of 198 t 30.5 g/L (16b)