Herbaceous biomass like Cynara is commonly high in potassium, chlorine and ash, which has been reported as a source of problems for combustion applications. An appropriate management of the potassium fertilisation is suggested as a way of improving the quality of the Cynara biomass for solid fuel applications. In this work a factorial experiment was designed involving two types of fertilisers, KCl and K2SO4, and two K rates, in order to study the effect of potassium fertilisation on the composition and thermal behaviour of Cynara biomass. The results proved that the potassium content of Cynara biomass increases with the potassium fertilisation. The thermogravimetric study showed that sintering phenomena can be expected at temperatures higher than 900 degrees C when the crop has been highly K-fertilised, irrespective of the type of fertiliser used, KCl or K2SO4. However, the SEM images taken of samples of the four K treatments of this experiment did not reveal signs of ash melting, although some particles with crystalline appearance appeared in the samples from highly K-fertilised treatments. (C) 2010 Elsevier Ltd. All rights reserved.