At the Experimental Farm of the Thünen Institute of Organic Farming the effect of sulphur fertilisation in form of MgSO4 and CaSO4 of a red clover-grass mixture was tested in the years 2013 -2015. At the beginning of the vegetation period clover-grass plots were fertilised in the first and second year of usage with 30 and 60 kg S ha-1 and were compared to unfertilised plots. The fertilisation resulted in significantly higher fresh weight and - with one exception of thew second year usage in 2013 - higher dry matter yields. The forage quality was significantly increased by sulphur fertilisation. Due to higher sulphur contents in the fertilised plots in the N/S-ratios showed values below the threshold of 15 for an adequate sulphur supply. The N-withdrawals increased in the fertilised plots in the first year of usage by 14 -25%, in the second year by 12 -45%. S-withdrawals were also increased by fertilisation and reached 20 - 40 kg S ha-1 compared to 12 - 15 kg S ha-1 in the unfertilised plots. In the majority of cases neither the level nor the kind of fertilzer showed significant effects on the parameters. Therefore a sulphur fertilisation of 30 - 60 kg ha-1 can be considered sufficient.
