Influence of Potassium Fertilizer Source and Application Rate On Potato Tuber Yield and Quality.

The potassium (K) fertilizer program used by a potato grower can influence the crop in several ways. Insufficient K can result in reduced tuber yield and smaller sized tubers. Potassium source differences have also been expressed through delays in tuber development and reduced tuber specific gravity. Information on source and application rate of potassium fertilizer is need for all potato growing regions. The objective of this study was to evaluate the effect of potassium fertilizer source and application rate on potato tuber yield, tuber size distribution and quality in the San Luis Valley of Colorado. The study was designed to evaluate the response of potato to four rates of K₂O (0, 40, 80, or 120 lb K₂O/acre) when applied as either muriate of potash (MOP) – KCl with or without the addition of sulfur (S) fertilizer, or as sulfate of potash (SOP) – K₂SO₄. Potassium source and rate of application significantly influenced tuber yield and tuber size distribution when SOP was compared to MOP with no S fertilizer (MOP-S) or MOP with S fertilizer added (MOP+S). At the low application rate of 40 lb K₂O/acre, SOP increased marketable (> 4 oz) tuber yield by 14% when compared to MOP+S.  For large marketable size (> 6 oz) tubers, SOP increased yields by 18% and 20%, when compared to MOP-S and MOP+S, respectively. At 40 lb K₂O/acre, SOP increased the yield of premium size (> 10 oz) tubers by 91% and 110% when compared to MOP-S and MOP+S, respectively. The use of SOP as source of K fertilizer reduced tuber external defects and increased tuber specific gravity. Data from this study indicate that the use of SOP as source of K fertilizer at a relatively low rate of 40 lb K₂O/acre increased marketable and premium size tuber yield, and improved tuber quality.