Effect of potassium on yield and processing quality attributes of potato

The productivity of potato in India is very poor at about 18 t/ha as compared to more than 45 t/ha in Europe. Low use of fertilizers and severely imbalanced use of N, P and K fertilizers are some of the reasons considered responsible for low production of potato. Potato crop is a heavy remover of soil potassium and removes 1.5 times the amount of nitrogen and 4-5 times the amount of phosphate. In India, a review of many field experiments conducted by PRII and CPRI on response of potato to potassium application revealed a yield increase between 1.0 t ha-1 and 5.2 t ha-1 at different sites. There was less weight loss and rottage of tubers with potassium application. Results of many experiments indicate that potassium nutrition influences tuber size, dry matter content, susceptibility to black spot bruise, after-cooking darkening, reducing sugar content, fry colour and storage quality. Considering the fact that tuber quality parameter are related to variety, to tuber maturity, growth and site conditions, water uptake and others, making of general recommendations on the optimal K fertilizer use is a complicated issue. Potassium application is reported to increase the size of tubers, especially, if K supply of the soil is low to medium. High K concentrations of above 2 % in tuber dry matter due to an over supply with potassium may lower the contents of dry matter. Potassium chloride seems more detrimental in reducing dry matter content of tubers and thus tuber quality for processing into chips and French fries. In most experiments, starch content in tubers was positively correlated to potassium application. About 1.8 % K in tuber dry matter is reported to be necessary for high starch concentration. Plants treated with K2SO4 translocated more photosynthates from the leaves and stems to the tubers compared with plants treated with KCl. Generally, K application decreased reducing sugars and lighten chip colour under low K nutrition levels. Though superiority of sulphate form of potassium has been established over the chloride form for processing tubers, it needs more detailed evaluation of the published data and also more specific and systematic studies under different climatic and varietal conditions to formulate the general potassium fertilizer recommendations.