Abstract

The main target of this research work is to evaluate the possibility of substituting partly or totally the expensive potassium fertilizers by natural deposits of feldspars bearing rocks. A field experiment was conducted to grow potatoes on poorly sandy soils. Four treatments were followed: control using K-sulfate only; ½ K-sulfate +½ K-feldspar; ¼ K-sulfate +¾ K-feldspars and K-feldspars only (according to the crop requirements of this element). Management and fertilization requirement of NPK were followed for potato crop. The total yield weight of vegetative plants as well as tubers could be arranged in the following order: 2^nd treatment> 1^st > 3^rd > 4^th. The K- content of the plants was significantly higher in the second treatment while the minor elements (Fe, Mn, Zn, and Cu) had no significant differences among the four treatments. High quality of potato tubers (morphological parameters) were observed in the fourth treatment in spite of the lower yield. The addition of equal rates of K-feldspar and K-sulfate resulted in the highest content of starch, monosucrose, protein and both vitamin C and A of potatoes. The advantages of applying K- bearing rock on poor fertility sandy soil can be related to their improvement of physical and chemical conditions particularly when combined with organic amendment. Also, the excessive application of relatively soluble chemical fertilizers has hazardous impact on environmental conditions since considerable proportions are usually lost through drainage which results in the pollution of water channels. From the economic point of view, the price of potassium sulfate fertilizer is about 7000 LE/ton while K- feldspar rock is about 600 to 800 LE/ton.

Key words: Potassium bearing rock - K-feldspar - potato crop - sandy soil.