Potassium supplying capacity of northeastern Portuguese soils

Abstract

In Portugal, the response to K application is often inconsistent with the Egner-Riehm values for available K. This is partly related to high K reserves of some soils. Twenty surface soils representative of different parent materials from NE Portugal were studied to determine their K supplying capacity. Continuous cropping with perennial ryegrass permitted the assessment of the relative ability of soils to release non-exchangeable K. Soils were classified in the range of available K from medium to very high. However, their ability to supply K in the short and long term are very different. In some soils K status measured by plant growth does not fall appreciably, whilst others are rapidly exhausted, and 30% of them are very deficient in K. The supplying capacity varied both with the nature of the parent material and the degree of weathering. The soils deficient in K are those derived from basic rocks and those with more weathered clay minerals. This is the case of the soils with the largest content of organic matter where the dominant clay minerals were kaolinite and vermiculite. Soils that have the highest capacity for supplying K are highly micaceous, like those developed from mica schists, phyllites or river alluvium. In fact the amount of K released from non-exchangeable form is well correlated with the amount of illite in the clay fraction. Soil types and K buffer power coupled with available K must be taken into account when planning any application of K.

Potassium supplying capacity in Argentine soils and plant uptake rate

“…The difference in nonexchangeable K uptake between both soils is exclusively related to their different initial concentration of exchangeable K given that both possess the same texture and mineralogy. This fact is in agreement with the findings of Badroui et al (1992) and Portela(1993).…”

“…For all soils, except for the Acuic Argiudol, plant K concentration in the first harvest is above the concentration considered sufficient for optimum ryegrass growth [1.6%, according to Portela (1993)], and is below this recommended concentration in the last harvest. The greatest values obtained are for the first harvests (0 to 30 days) while there is a gradual decrease in subsequent ones, until, by the fifth, the value is 10% of the first (Figure 1).…”

Potassium Fixation and Release Characteristics of Several Normal and K-Exhausted Soils in the Middle and Lower Reaches of the Yangtse River, China

“…However, it has been recognized that only measuring exchangeable K is not a true reflection of K availability for many soils (Portela 1993;Markewitz and Richter 2000), because the release of nonexchangeable K can replenish soil exchangeable K so as to supply crop uptake. Potassium release is a procedure in which available K in the soil can be supplemented.…”

Solutes in overland flow following fire in eucalyptus and pine forests, northern Portugal

“…At the burnt sites, N, P and K are concentrated in the ash and upper mineral soil layers (Table II). The lower subsoil nutrient concentrations re¯ect the low ion exchange capacity of the soils in the region and their susceptibility to leaching (Portella, 1993).…”