The potassium Q/l relationships of soils given different K manuring

SUMMARY The potassium quantity/intensity (Q/I) relationships, which relate change in exchangeable K content (Q) to change in activity ratio were measured in soil samples from manuring experiments at Rothamsted and Woburn. Within each experiment, Q/I curves for different K-manuring treatments were super-imposable on each other and on the curve relating exchangeable K to Io, the activity ratio at which the soil neither gains nor loses K. The distances on the Q axis between the curves were equal to the differences in exchangeable K. The buffer capacity, dQ/dI, was related to the K saturation of the cation exchange capacity (CEC) by the equations (Q and CEC in m-equiv/100 g) Broadbalk and Hoosfield soil, and for Barnfield soils (b= 3·08; m= 1·0) and for Woburn market garden soils (b =2·41; m= 0·6) but for soils from other Woburn experiments, dQ/dl did not vary significantly with Q/CEC.