Switchgrass (Panicum virgatum L.) is a bunchgrass native to North America recently successively cultivated as an energy crop. The use of compost as soil amendment is a universal practice well known for its benefits to soil properties and plant growth. This study aimed to assess the possible benefits of compost addition on the growth parameters of four switchgrass populations, the octaploids Shelter, Shawnee and Dacotah, and the tetraploid Alamo, in pot experiments. Three growing media were

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... red by mixing peat (P) with each of three different composts, a green compost (GC), a mixed compost (MC) and a coffee compost (CC), at the percentages of 5%, 10% and 20% (v/v). Results obtained showed that, with respect to the use of P only, all compost mixtures exerted positive effects on root, shoot and primary leaf lengths and on the fresh weight of the different switchgrass populations. In particular, GC/P and MC/P mixtures appeared more efficient at 5% and 10% of compost, whereas CC/P mixtures produced the best results at 10% and 20% of compost. The effects of composts were more evident for the Shawnee population and less for the Shelter one, thus indicating an involvement of the genotype in the plant response.