Effetti su alcuni microrganismi ed attività biologiche del suolo provocati dagli erbicidi sulfonilureici usati in post-emergenza nella coltivazione del Mais

{rrff""tt on some microrganisnts and bíologìcal E t activities of the soil caused by sulfonilurea herbicides used ín post-emergence ín maíze crops. The effects of sulfonylurea herbicides, Thifensulfuron- methyl, Rimsulfuron and Primisulfuron, used in post-emergence maize crops, have been evaluated on some microorganisms and biological activities of the soil. The herbicides did not have any significant effect on îotal microflora. Basal respiration was stimulated by the tested herbicides, and CO2 emis-sion, determined by adding sulfonylureas (1 mg ml-l S, was 2-3 times greater than the control. Comparison of respiratory activity between Thiftnsulfuron- meîhyl and other nutrients showed that the herbicide caused increases in CO2 emissions lower than those due to glucose and urea, but greater than cellulose. The increased respiratory activifit ceased in 8-12 days, indicating that the microflora quickly degraded the sulfonylurea. The effects of pesticides on the tesîed microorganisms showed that Primisulfuron (1 mg mt-I ) partially inhibited the growth of Ag ro bacte rium radiobac te r, Enterobacter sp., Pseudomonas sp. and Azotobacter chroococcum. Rimsulfuron and Thifensulfuron-methyl, at I mg ml- ', inhibited the parent strain of A. chroococcum Azwt, while the mutant strain AzcapL was inhibited even at concentrations of tOO pg mf I. Sulfunylureas partially inhibited the growth of the algae Scenedesmus acutus and Anabaena azollae, but did not affect the development of the cyanobacterium Spirulina platensis. The greater sensitivity of A-chroococcum mutant Azcapl should lead to the evaluation of the consequences that new pesticides might cause to the balances achieved with previous management.