A 100 g sample of a soil has been determined to contain the exchangeable cations in these amounts: Ca 2+ = 90 mg, Mg 2+ = 35 mg, K + = 28 mg, and Al 3+ = 60 mg. (a) What is the CEC of this soil? (b)...

A 100 g sample of a soil has been determined to contain the exchangeable cations in these amounts: Ca²⁺
= 90 mg, Mg²⁺
= 35 mg, K⁺
= 28 mg, and Al³⁺
= 60 mg. (a) What is the CEC of this soil? (b) What is the aluminum saturation of this soil?

Explain why there is environmental concern about the adsorption by soil colloids of such normally beneficial substances as antibiotic drugs and natural insecticides.