Considerable evidence exists that both N and K influence potato (Solan
um tuberosum L.) yields and quality. The impact of nutrients on tuber
quality parameters under field conditions should be identified so opti
mum management practices can be utilized. We evaluated the N and K fer
tilization by K-sources effects on concentrations of nutrients, reduci
ng sugars, sucrose and starch in the stem and apical tuber ends from t
wo irrigated field experiments with the Russet Burbank cultivar. Nitro
gen rates of 0, 112, 224 or 336 kg ha-1 were combined with selected K
rates of 0, 112, 224 or 448 kg ha-1 as either KCl or K2SO4 arranged as
an incomplete factorial. A multiple linear regression model was fit t
o the data and used to predict the response surface for a complete fac
torial for each K-source. Nitrogen applications increased or decreased
reducing sugars in the apical and stem ends, respectively. Potassium
decreased reducing sugars in both tuber ends. Sucrose was higher in th
e apical end than in the stem end but was not appreciably affected by
fertilizer treatment. Nitrogen and potassium applications reduced dry
matter and starch concentrations in both tuber ends. Potassium had a s
maller effect on the apical end when starch was expressed on a dry wei
ght basis, indicating that increased water content was a factor in the
K effect. Both N and K concentrations in the tuber ends were negative
ly related to starch concentrations, but the relationship was differen
t for the apical and stem ends. Tuber Cl concentration indirectly affe
cted starch concentrations in the stem end when KCL was applied. The K
fertilization effect on specific gravity depended upon the K concentr
ation in the harvested tuber and was independent of K fertilizer sourc
e. These data illustrate the effects of preplant N and K fertilization
rates on final tuber quality parameters. Additional studies are neede
d to further define the effects of nutrient concentrations at differen
t plant growth stages.