EFFECT OF SOIL FERTILIZATION AND FOLIAR SPRAY OF POTASSIUM ON VEGETATIVE GROWTH AND YIELD AND ITS COMPONENTS OF SWEET POTATO

Abstract

Two field experiments were carried out at a farm in Dakaelte village neighbor the experimental farm of Faculty of Agriculture, KafrelsheikhUniversity during two successive summer seasons of both years 2008 and 2009. The main objective of this research was to study the effect of soil K levels fertilization (25, 50, 75 and 100 kg K2O/fed and foliar spraying (twice) with K (zero and 0.5% K2O equal 6 kg K2O/fed.) on vegetative growth and root yield and its components of sweet potato cv. Abees. The experiment’s design was a split-plot with four replications. K-sulphate fertilizer was used as soil and foliar fertilization. The results indicated that, raising K levels from 25 up to 75kg K2O/fed. significantly increased vegetative growth and roots yield. Application of either soil K level of 75kg K2O/fed. (alone) or foliar spraying with K (twice) at concentration of 0.5% K2O (alone) significantly increased vegetative growth characters (stem length, numbers of leaves and branches, leaf area/plant, vine fresh weight, dry matter(% ) of vine and total chlorophyll of the 5th leaf), total roots yield (as number, weight and increase %), marketable roots yield (as number, weight, increase % and percentage of marketable yield from the total yield) and average root weight for total yield, but application of either K levels of 75 and 100 kg K2O/fed. or foliar spray of K significantly decreased non-marketable roots yield (as weight and decrease % and its percentage from the total yield). The increases (%) in weight of total and marketable yields resulted from using 75 kg K2O/fed. over low K level were 22.7 and 33.1% (as average of two seasons), respectively. Likewise, the increases % in total and marketable yields from using foliar spraying with K (at 0.5% K2O) over the unsprayed were 18.9% and 25.1% (as average of two seasons), respectively. The combined interaction between soil K levels fertilization and foliar K application caused non-significant effects on vegetative growth characters and root yield and its components on both seasons. Although interaction treatment of 75 kg K2O/fed (as soil application) plus foliar spraying with K at 0.5% K2O (equal 6 kg K2O/fed) tended to increase most of the previous vegetative growth characters, total yield (42.7%), marketable yield (68.0%) and average root weight of total yield, but decreased non-marketable yield in both seasons. Such treatment of the interaction saved K fertilization by 19-25 kg K2O/fed. compared with the high soil k level (100kg K2O/fed.) alone or foliar K application .