N-2 fixation and growth of legumes as affected by sulphur fertilization

The influence of three sulphur application rates in combination with two nitrogen application rates on N-2 fixation and growth of different legumes was investigated. N was applied as N-labelled (NH4NO3)-N-15-N-15. The N-15 isotope dilution technique was used to estimate N-2 fixation. At both N increments dry matter yield was highest with high S supply. Independently of the N supply, the high S application rate resulted in a significantly higher N accumulation, which was mainly caused by a higher N-2 fixation rate. With the grain legumes the weight of nodules was increased by the high S application rate. The higher number of nodules per pot with optimum S supply was the result of a better root growth. Rates of acetylene reduction correlated significantly with S supply.