In greenhouse experiment, straw alone or with different phosphates, produced a negative effect on the growth of vetch crop in the first year of its application possibly due to immobilization of nitrogen and production of phytotoxic substances. Phosphate immobilization was not the cause of lower yields as noted in treatments with straw. A positive residual effect of straw on yield and P uptake was noted only in the second year. The residual effect of straw favoured the accumulation of humus and fulvic phosphates. The role of fulvic acid in the mobilization of mineral phosphates is emphasized. Precomposting of straw for a certain period with soil before the sowing of crop seems desirable to overcome the effects of immobilization of nitrogen and phytotoxic substances produced in the initial phase of its decomposition.