Summary:Fenuron, monuron, diuron, siduron, linuron and neburon were tested for their inhibition of soil urease activity in order to investigate relationships between fertilizers and herbicides.The inhibition of urea hydrolysis in the selected soils was 10–33% for fenuron, 10–39% for monuron, 10–35% for diuron, 8–38% for siduron, 9–36% for linuron and 12–30% for neburon. In the field greater effects might be expected since the fertilizer/herbicide ratio would be lower than the one considered here.Some agronomic aspects of the relationship between fertilizers and herbicides ar