Abstract: A field experiment was carried out at the Experimental Farm of the Faculty of Agriculture, Moshtohor,
Benha University, Qalubiya Governorate, Egypt during the two successive seasons of 2010 and 2011 to
investigate K fertilization by using feldspar-K and sulphate-K and biofertiliztion with a mixture of N-free fixing
bacteria, P-dissolving bacteria and silicate dissolving bacteria on growth of potato (Solanum tuberosum L cv.
Sponta). The experimental design was a randomized complete block, factorial in 3 replicates. Factors of the
experiment and their treatments were as follows: (A)K-addition, five treatments :(A ) 100% dose sulphate- 1
K(SK), (A ) 75% dose as SK + 25% dose as feldspar-K(FK),(A ) 50% SK + 50% FK,(A ) 25% SK + 75% FK and 2 3 4
(A ) 100% dose of FK, the full dose of K was 300 kg K/ha ,(B)Biofertilization, two treatments:(B ) no addition 5 0
of biofertilizer and (B ) addition of biofertilizer. Nitrogen and phosphorus were added to all treatments at a rate 1
of 350 kg N/ha and 75 kg P/ha. Plants were sprayed 3 times with Fe, Zn, and Mn-EDTA at rate of 0.5 ,0.2 and
0.15 kg/ha, respectively, at 55, 65 and 75 days after planting in each season. Treatment A gave the highest yield 3
(tubers and shoots), macro nutrient uptake (N, P and K) in tubers and shoots, tuber size, starch content, leaf
area, and total chlorophyll. Increasing the dose of feldspar-K increased nitrate content in tuber. Biofertiliztion
increased yield (tubers and shoots), macro nutrient uptake (N, P and K) in tubers and shoots, tuber size, starch
content, leaf area, and total chlorophyll. It decreased slightly nitrate content in tubers.