POTATO (Solanum tuberosum L.) TUBER YIELD AND QUALITY AS INFLUENCED BY POTASSIUM FERTILIZER IN UASIN GISHU COUNTY, KENYA

Abstract

Irish potato is the second most important food crop after maize in Kenya. However, the national average tuber yield is 9.8 tonnes ha-1 which is low compared to optimum production of 41 tonnes ha-1 . There is unmet production demand for potato tubers with high processing quality in Kenya, which can meet international standards for products such as chips and crisps. Potassium (K) is one of the macronutrients taken up in larger amounts by potato and is known to enhance both its yield and quality traits. However, researchers have not reached a consensus on whether K should be applied in Kenyan farms. To determine the effectiveness of potassium fertilizer on tuber yield and quality enhancement as well as profitability due to the fertilizer application, a field experiment was conducted at University of Eldoret farm in Uasin-Gishu County during the short and long rains seasons of 2020 and 2021 respectively. Two sources of potassium, muriate of potash (MOP) and sulphate of potash (SOP) were used at rates of 0, 60, 120, 180 and 240 kg ha-1 of K during the short rains and 0, 30, 60, 90, 120 and 180 kg ha-1 of K during the long rains. Treatments were laid out in a Randomized Complete Block Design replicated three times in a 2x5 factorial during the short rain and 2x6 factorial during the long rain season. Destiny variety of potato was planted. The rate of 120 kg ha-1 of K as sulphate of potash increased marketable tuber yield by 51% relative to the control in the short rains. In the long rains, 30kg ha-1 of K as muriate of potash gave tuber yield of 40.54 tonnes ha1 and profit of 111.86%. SOP significantly enhanced tuber dry matter compared to MOP by 5.6% in both seasons. Further, 180 kg ha-1 of K in form of SOP gave the highest tuber concentration of vitamin C (19.56 mg g -1 ) but similar MOP rate reduced vitamin C content by 5.89 mg g-1 compared to control during long rains. In the short rains, 120kg K/ha gave the highest tuber starch content while similar rate of SOP recorded 4.77% lower tuber starch content. The highest rate of MOP (240kg K/ha) significantly lowered the tuber starch content compared to control. It was concluded that in areas with similar ecological conditions as the study area, tuber dry matter content can be increased by application of sulphate of potash and potato farmers can optimize on their profits and tuber content of vitamin C by application of 30kg/ha of K as MOP and 180kg/ha K as SOP respectively during the long rain season. It is recommended that a similar study be done in different soils where potato is grown and with different varieties.