Effect of Some Pesticides on Soil Microorganism Grown in Soil with Organic Matter

Use of large quantities of pesticides in Saudi Arabia could entail harm effects on the soil environment as well as on the non-target organisms, especially the essential microbial groups related to soil fertility. Soil content of organic matter affected pesticides role in soil, for that, an experiment, was designed to study the effect of different organic amendments such as glucose and clover at 1 % on the behaviors of soil microorganisms in the present of pesticides (lannate or Diazinon). The mixed soils were incubated at    28 ± 2 ºC with 70 % WHC. Samples were taken periodically after 0, 1,2, 3, 4, 5 weeks to estimate the microorganisms groups (Total bacterial colony counts, fungi, actinomycetes, aerobic cellulose decomposers, phosphate dissolving bacteria,Azotobacter and  Azospirillum), organic carbon and total nitrogen contents in soils (clay loam and sandy) were also determined. Data Showed that, the addition of organic matter substance of glucose or clover at the rates of 1 % to both soils types examined in this study weakened the inhibitory effect of lannate and diazinon, especially when using the doubled dose. The use of clover was better than the use of glucose as an organic substance in both soil types. Most frequently the inhibitory effect of diazinon on the soil microorganisms was decreased in the presence of organic matter substance. While it was increased in case of lannate with the doubled dose in particular. Carbon consuming was decreased due to pesticides application , also nitrogen quantity in soil was affected at the end of experiment