Transformation of forms of potassium in soil during long-term potassium fertilization

Abstract

Studies on the different forms of potassium in a light loamy sod-podzol acid soil after a 43-year period of fallow or cultivation of winter rye or potatoes, with the application of various fertilizer combinations showed the following: — 1. Under continuous fallow, there is a considerable migration of potassium (from that applied with the fertilizers) to the sub-plough horizon up to approximately 20 per cent. About 15 per cent of the potassium applied can apparently move even below the 40-cm layer. The loss of potassium was particularly large on the non-phosphate-fertilized plot (NK), amounting to 42 per cent. Because of the physiological and biological acidity of ammonium nitrate, the soil in this plot acquires unfavourable properties and partially loses its colloids, these migrating along with adsorbed potassium to deeper horizons of the profile. 2. Fixation of potassium (transformation into unreplaceable form) occurs in the plough layer and constitutes 11 to 14 per cent of the applied potassium; on the PK and NPK plots, fixation increases to 35 per cent. 3. Winter rye intensively utilizes the potassium applied, and, with exception of K plot, a further absorption of potassium from the soil takes place, the magnitude depending on the accompanying fertilizers — on the NPK and NK plots, 19–21 kg but on PK plot only 1,4 kg per hectare per annum of potassium alone results in a partial fixation by the soil in a non-exchangeable form (on the average 8 per cent annually). 4. Potatoes also fully utilize potassium applied with fertilizers; there is also a large absorbtion of potassium from the soil reserves — on the average on the NPK plot, 18,7, PK plot, 17.3, and NK plot, 4.6 kg per hectare per annum. A marked impoverishment in the potassium content of the sub-plough horizon of soil was observed. Fixation of potassium in an unreplaceable form takes place on the K plot and on the average reaches 8.9 per cent of the applied potassium per annum.