Effects of Source and Rates of Potassium Fertilizer on Yield Traits and Potassium Use Efficiency of Potato in a Kenyan Ferralsol

Aims: Potassium (K) is one of the nutrient elements taken up in large amounts by potatoes, yet there is little research output on K fertilization of the crop in Kenya, due to the assumption that its natural soil reserves are sufficient for the production of most crops. The study objective was to determine the influence of two K sources (muriate of potash – KCL and sulphate of potash – K2SO4) on K use efficiency and tuber yield components of potatoes in one agro-ecological zone of Kenya.

Place and Duration of Study: The experimental site was the University of Eldoret farm in Kenya, located at latitude 0o574942’ N and longitude 35o300772’ E, during the middle - second rains season (S1) and middle rains season (S2) of 2020 and 2021 respectively.

Methodology: Treatments were: 0 kg K ha-1 (control), 60,120,180 and 240 kg K ha-1 in S1 and 0, 30, 60, 90, 120 and 180 kg K ha-1 in S2, supplied in the form of KCL and K2SO4. Treatments were laid in a Randomized Complete Block Design in 2x5 and 2x6 factorial arrangements in S1 and S2 respectively. The potato variety planted was Destiny. Data collected included: Agronomic efficiency of K (AEK,), total tuber yield, two categories of seed yield (Size 1 tubers with diameters of 28- 45 mm; Size 2 tubers with 46 - 60mm diameter), total seed yield and ware yield (tubers with diameters over 60mm).

Results: During the drier S1, the application of 120 kg K ha-1 in the form of K2SO4 significantly (P < .001) increased the yield of size 1 tubers, total seed yield and total tuber yield. The total tuber yield increment from this K rate was only 12.6 % of the varietal potential yield, and its AEK was 0.042 tonnes of tubers kg-1 K. Therefore its application may not be economically viable. During the moisture-sufficient S2, all K fertilizer treatments in the form of KCl and 90 kg K ha-1 in the form of K2SO4, contributed a yield increase of 58.1 - 68.6% and slightly exceeded varietal yield potential. Additionally, 30 kg K ha-1 of KCL gave the highest AEK of 0.5 tonnes of tubers kg-1 K and consistently enhanced the yield of all potato sizes, except size 1.

Conclusion: Under similar ecological conditions as S2, potato farmers can achieve the highest AEK and potential tuber yield with the application of 30 kg K ha-1 of KCL. However, more trials on K nutrition in potatoes need to be done in diverse environments.