The thesis can be divided into two parts. The first part is devoted to a comparison of the two methods, the steam distillation and Technicon automated methods, used for the determination of inorganic nitrogen. To test the precision and accuracy of the two methods, a 5 ppm standard of both ammonium and nitrate nitrogen was used for the steam distillation method and a 1 ppm standard of both ammonium and nitrate nitrogen was used for the Technicon method. By the steam distillation method the % recovery for the NH4-N standard was 95.2% and for NO3-N 94%. The major factor affecting the recovery of nitrogen was the loss of ammonia at the joint between the spray trap and the distillation flask. The joint on the apparatus was modified and tests achieved the recoveries for NH4-N of 99.6% and NO3-N of 99.6%. The inorganic-N was then determined by the Technicon AutoAnalyzer II. 1 ppm standards of both ammonium and nitrate-N prepared in water and 2M KCl were analysed. Standard deviations were 0.0275 and 0.0025 in water and KCl respectively for NH4-N and 0.0056 and 0.0051 in water and KCl for NO3-N. The standard deviation of NH4-N in water was very high. One source of variability was identified in that particular flasks consistently gave low results. A possible reason for the variability is due. to the adsorption of NH4+ ion by negative sites on the glass walls of the volumetric flasks. NO3- ion would not be affected by such negative adsorption sites and in KCl, K+ would be adsorbed in preference to NH4+ as K+ would be present at a much higher concentration. Both steam distillation and Technicon methods are found suitable in their own places. Though distillation procedures are time consuming they are simple, accurate and less expensive and not affected by the various organic and inorganic substances present in soil extracts. Using the Technicon AutoAnalyzer II a concentration as low as 0.001 mug/ml can be detected and large numbers of samples can be analysed quickly with a high degree of reproducibility. But these automated methods are very sophisticated and it is very difficult to run such complex systems which require a skilled operator and well furnished laboratories. So for developing countries steam distillation methods are more preferable. The second part of the thesis is devoted to testing the effects of three pesticides, captafol, carbaryl and malathion on three selected microbial processes, the phosphatase, dehydrogenase activities and nitrification in two soils of different properties. The two soils used were Darvel Series, a sandy clay loam of pH 6.4 and 8.82% organic matter content and Dreghorn Series, a sandy soil of pH 6.8 and 5.64% of organic matter content. Phosphatase activity involved the colorimetric estimation of p-nitrophenol released from p-nitrophenyl phosphate after incubation at 3
