Studies on Soil Potassium Ii. The ‘Immediate’ Q/I Relations of Labile Potassium in the Soil

Abstract

The Q/I relations of labile soil K relate its availability or intensity (I) to the amount (Q) present. The activity ratio aK/,/(aca+Me) has already been proposed as a measure of the intensity factor (Part I). The ability of a soil to maintain the activity ratio against depletion by plant roots is governed partly by the character of the pool of labile K and also by the rate of release of fixed K, and by the difTusion and transport of K ions in the soil solution. We may isolate the Potential Buffering Capacity of the pool of labile K by determining the Q/I relation over short periods. Such immediate QlI relations have been determined for a number of soils. They are all linear over the range of activity ratios commonly encountered in agricultural soils and approximate to familiar ion-exchange equations. At low values of the activity ratio the Q/I relations are all curved and asymptotic to the Q-axis.The effects of drying, pH, the addition of lime or K fertilizers, and changes in temperature on the form of the Q/I relations are reported.Oven-drying a soil, particularly if repeated, appears to cause proportionately more K than Ca to be fixed in the fine clay fraction.

The effective relative affinity for magnesium and potassium of some soils from the North Island, New Zealand

“…In the Marton soil the pattern was similar, but the general level of the Gapon coefficient was very much higher than on the two previous soils. In contrast, in the Taupo soil the level of exchangeable K was insensitive to variations in the K/Ca activity ratio ( Table 2), suggesting that under the conditions of this experiment K was held almost entirely by specific adsorption (Beckett 1964a), and that this soil was almost incapable of holding K on sites other than specific ones.…”

Potassium adsorption characteristics of five different textured soils under enset (Ensete ventricosom cheesman) farming systems of Sidama zone, South Ethiopia

“…Soils were analyzed by the quantity/intensity procedure based on the method outlined in Beckett (1964). A stock solution of potassium chloride, 10 mmole/L KCl and calcium chloride, 10 mmole/L CaCl2 were prepared separately.…”

Potassium dynamics under enset (Ensete ventricosom cheesman) farming systems of Sidama zone, Southern Ethiopia

“…Soil samples selected were analyzed by the Quantity/Intensity procedure based on the method outlined in Beckett (1964). A stock solution of potassium chloride, 10 mmole/L KCl and Calcium chloride, 10 mmole/L CaCl2 were prepared separately.…”

“…However, to assess the conditions of potassium uptake by plants, the extensive parameters such as potassium, calcium and magnesium contents of soils are also required (Yong-Hong, 2010). In this case, the activity ratio (AReK) described by Beckett (1964) is one of the satisfactory measures of the K dynamics and its availability, because it measures the chemical potential of labile K present to the chemical potential of labile calcium plus magnesium in the same soil.…”