Impact of Selected Pesticides on Some Soil Enzymes Activity in Soil Cultivated with Wheat Crop

Wide areas of agricultural soil are grown with wheat crop in Egypt using different groups of pesticides especially; herbicides and fungicides, it is important to evaluate the potential risks of pesticides residue to non-target organisms in agro-ecosystems such as soil microorganisms which could be indicated by determining certain soil enzyme activities. Therefore, a field experiment was conducted at Research and Experimental Farm, Faculty of Agriculture, Abees region - Alexandria- Egypt to investigate the effects of some pesticides on some soil enzymes activity in soil cultivated with wheat crop. Three herbicides namely; Granstar® 75% (at rates of 0, 4 and 8 g/fed), Panther® 55% SC (at rates of 0, 300 and 600 ml/fed), Topik® 15% WP (at rates of 0, 70 and 140 g/fed) and one fungicide; Sumi-eight®12.5% WP (at rates of 0, 17.5 and 35 ml/100 l). The pesticides were applied during the growing season of wheat on Jan 19 and March 10, 2013. The soil samples were collected at the end of growing season of wheat crop May 2013 for three soil depths, i.e. 0-5, 5-10 and 10-20 cm. Enzymes activity were assayed in triplicate air-dried samples. Three soil enzymes were tested, i.e. catalase, urease, and phosphatase. Enzyme activities were assayed in triplicate air-dried samples. The results indicated that Panther has highest activity soil and Granstar has less activity. Also, the concentration of pesticides significantly (p<= 0.05) decreased the activity of soil enzymes in which increasing the application rate decreased the enzyme activity. The activity of soil enzymes was significantly (p<= 0.05) increased as soil depth increased. The surface layer (0–5 cm) has the least value of enzyme activity. These findings match the fact that the pesticide transport in soil is low and the pesticide did not reach more than 10 cm. In general, the pesticides decreased the activity of soil enzymes and this decreasing increased with increasing the pesticides application rate. Also, the decreasing of soil enzyme activity was less with increasing soil depth.