EFFECT OF SOME PESTICIDES ON ASYMBIOTIC N-2-FIXATION IN EGYPTIAN SOIL

The effect of the application of a group of pesticides (Temik®, Stomp®, Dinoseb, Nata®, Dursban®, and Simazine 1 on N2-ase activity in Giza clay-loam soil under maize cultivation was investigated in the presence of 1 to 2% glucose or malate amendments. Field concentrations of all pesticides showed different inhibitory effects, and the effects increased with increased doses (10-and 100-fold) and incubation period (11 days). Temik and Stomp more seriously inhibited N2-ase activity than Dinoseb and Nata; Simazine and Dursban had the lowest effect. The effect of the field dose of Stomp on the patterns of N2-ase activity and development of N2-fixing spirilla and azotobacters in soil amended with glucose or malate was followed for a period of one month. Inhibitory effects on N2-ase activity as well as numbers of asymbiotic N2-fixers were marked during the first week of incubation, followed by a step wise recovery to normal levels by the end of the experiment. The deleterious effect of the tested pesticides was repeated in pure cultures of certain isolates of N2-fixing spirilla and azotobacters. © 1979 Springer-Verlag New York Inc.