This Test Guideline describes a laboratory test method designed to investigate the long-term effects of chemicals, after a single exposure, on nitrogen transformation activity of soil microorganisms.

Sieved soil is amended with powdered plant meal and either treated with the test substance or left untreated. For agrochemicals, a minimum of two test concentrations are recommended (five for non agrochemicals) and these should be chosen in relation to the highest concentration anticipated in the field. The soil is divided into three portions of equal weight (six for non agrochemicals). Two portions are mixed with the carrier containing the product (five for non agrochemicals), and the other is mixed with the carrier without the product (control). A minimum of three replicates for both treated and untreated soils is recommended. After 0, 7, 14 days and 28 days of incubation, samples of treated and control soils are extracted with an appropriate solvent, and the quantities of nitrate in the extracts are determined. All tests run for at least 28 days. If, on the 28th day, differences between treated and untreated soils are equal to or greater than 25%, measurements are continued to a maximum of 100 days. Results from tests with multiple concentrations are analysed using a regression model, and the ECx values are calculated.