The 2013 reform of the European Common Agricultural Policy tries to support farmers willing to follow environment- friendly rural practices, by the so called “green payment”. Within this framework, it is suggested that governments and regions should maintain a certain ratio of the area of permanent grasslands to the total Utilized Agricultural Area according to the greening rules of the reform. However, the weak economic performance of permanent grasslands does not encourage farmers to invest into their conservation. This fact persuaded us to revisit our old unpublished data, obtained by experiments on the use of chemical fertilizers in permanent grasslands. By this reanalysis we hope to further support the new European policy with the perspective to find a trade-off between the conservation of the biodiversity and the economic productivity of permanent grasslands. Of the many possibilities we have chosen to present the results of two experiments, one in Italy and the other in Slovakia. The main reason for this choice was that these two studies followed complementary strategies of fertilization that appeared useful to detect both the single and the synergistic effects of N, P, and K on the relationships between yield and species diversity. The results of cluster and diversity analysis suggest that chemical fertilization should be carefully planned according to soil conditions, since different treatments may have the same effect on the floristic and vegetation patterns of grasslands. These results, according to similarity theory, allow to choose the least expensive and polluting combination of N, P and K from those that, according to the species combinations, are assigned to the same cluster.