A RAPID TISSUE TESTING METHODOLOGY FOR OPTIMUM POTASSIUM FERTILIZATION OF POTATO GROWN UNDER SUBTROPICAL SHORT-DAY CONDITIONS

Field experiments were conducted at the Central Potato Research Statio n, Jalandhar (Punjab) during 1989-90 and 1990-91 on a sandy loam soil (Typic Ustochrept) to develop a tissue testing methodology for determi ning the optimum dose of K to be applied as a side dressing at the tim e of earthing up, based on leaf tissue analysis. The sixteen treatment s consisted of all combinations of four levels of K applied as basal a t planting and as side dressing at the time of earthing-up (30 days af ter planting (DAP) in two potato cultivars, Kufri Jyoti and Kufri Chan dramukhi. The combined application of basal and side dressed K was sup erior in increasing tuber yield of potato compared to their individual application. The concentration of K in leaf blade or petiole at the e arly stages (29-40 DAP) was more related to basal K than to basal+ sid e dressed K, while at the later stages (40-60 DAP) it was more related to basal+side dressed K than to basal K. This suggests the need to ap ply both basal as well as side-dressed K to maintain a high K concentr ation in the leaf tissues throughout the crop growth cycle. A methodol ogy to estimate the optimum dose of K to be side dressed from leaf tis sue analysis is described. Critical K concentrations in leaf tissues a t different growth stages are reported for both potato cultivars.