An important pathway of atrazine degradation in perfusion systems of three soils was chemical hydrolysis to hydroxyatrazine. Ultraviolet spectrophotometric analyses of the perfusates showed the presence and accumulation of hydroxyatrazine. Atrazine degradation followed first‐order kinetics in soil‐free, sterilized soil and perfusion systems. An increased rate of atrazine hydrolysis in an acid soil was consistent with the effect of pH on hydrolysis. No microbial degradation of atrazine was detected following inoculation of a soil‐free atrazine medium with perfusates. An increased rate of hydrolysis in the presence of sterilized soil was postulated to result from soil adsorption of atrazine. Soil pH and organic matter content largely controlled the rate of atrazine hydrolysis; for soils of similar pH, atrazine degradation rates increased with increased atrazine adsorption.

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The effect of pH of the buffered saturating solution on the cation‐exchange capacity (CEC) of 60 Wisconsin soils was determined within the pH range 2.5 to 8.0. The relative contributions of clay and organic matter to total CEC were measured using multiple regression analyses; the independent variables were clay and organic matter contents and the dependent variables, CEC at pH 2.5, 3.5, 5.0, 6.0, 7.0, and 8.0. The average CEC of the organic matter at each pH value was 36, 73, 127, 131, 163, and 213 me. per 100 g., respectively; while that of the clay was 38, 46, 54, 56, 60, and 64 me. per 100 g. Within the limits of the standard errors of the regression coefficients, CEC of both clay and organic matter increased linearly with pH. The regression equations indicated that the mean relative contribution of organic matter to total soil CEC in this group of soils varied from 19% at pH 2.5 to 45% at pH 8.0; the mean organic matter and clay contents of the soils studied were 3.28% and 13.3% respectively. Coefficients of multiple correlation varied from 0.927 at pH 3.5 to 0.959 at pH 8.0.

The effect of soil pH on rates of ammonification and nitrification was studied. Soil samples which ranged in pH from 4.7 to 6.6 from an established lime and N fertility experiment were used. Soil pH values in the lime plots have been relatively constant for several years. Soil pH did not affect rates of ammonification appreciably; however it had a significant effect on nitrification rates. Length of the delay period (t′) was increased and rate of NO3‐ accumulation (Km) decreased with a decrease in soil pH. Previous field N treatments increased the length of t′ at low pH and decreased t′ and Km at high pH. Nitrification rates and production of NO3‐ were similar for soil pH values of 5.3, 6.0, 6.3, and 6.6 with a different pattern at pH 4.7.