VARIABILITY OF BIOASSAYS WITH METSULFURON-METHYL IN SOIL

A total of 74 independently run bioassays with soil incorporated metsu lfuron-methyl from 12 different laboratories was analysed by a logisti c dose-response curve to assess the precision of regression parameters and relate ED(50) to soil properties. The potency in terms of ED(50) of metsulfuron-methyl in Brassica rapa L., which was used by all labor atories, varied between 0.05 and 3.9 g a.i. ha(-1). ED(5)0 was negativ ely correlated with pH and positively correlated with organic matter. The majority of laboratories had EDso within the interval 0.1-1.0 g a. i. ha(-1). At one laboratory using three test species, the most sensit ive species was Beta vulgar's L. followed by Brassica rapa L, and Lepi dium sativum L. The coefficients of variation were smallest for the ED (50) and ED(90) response levels and largest for the ED(10). The slope of the response curves had considerably lower coefficients of variatio n than the EDs. The results are discussed in relation to a previous co llaborative bioassay study. Finally it is suggested that standardizati on of bioassays with herbicides could be achieved in the same way as s tandardization of chemical analyses.