Lachover, D., Division de Chimie Agricole, Département d'Agronomie, Institut National Universitaire d'Agriculture, Rehovoth, Israel
Feldhay, H., Division de Chimie Agricole, Département d'Agronomie, Institut National Universitaire d'Agriculture, Rehovoth, Israel

A study of the relative effectiveness of three different sources of potassium was made on light clay textured soil from the Esdraelon Valley and on silt-loam from the Coastal Plain. Experiments were carried out in large containers. The data obtained showed a correlation between exchangeable potassium reserves and the yield response to potassium fertilization in general. On the basis of potato yield only, there was no response in the light clay soil (with a high level of exchangeable potassium) and a significantly good response in the silt-loam soil (which is lower in exchangeable potassium). No differences in potato yield were found on either soil from the three potassium sources. In the silt-loam soil it was found that potassium metaphosphate slightly lowered the dry matter content in comparison with potassium chloride and the starch in comparison with potassium chloride and potassium sulfate. Differences between fertilized and control plots were not significant. A discussion is presented on the chloride content in potato leaves and the comparative levels of exchangeable potassium in the control and fertilized soils. © 1964 Uitgeverij Dr. W. Junk.