Impact of straw applied as fertilizer on phosphorus mobility in common chernozem. The mobilizing role of unfermented straw, incorporated as fertilizer, on the phosphorus in soil and on that contained in chemical fertilizers has been demonstrated in a field experience performed on common chernozem at the Experimental Station of the Institute of Pedology, Agro-chemistry and Soil Protection „NicolaeDimo”, the Republic of Moldova. The specific increase of phosphorus available from the straw used alone in a dosage of 4 t / ha was of0.25 kg P₂O₅/ t straw and of 0.38 kg P₂O₅/ straw when the dosage of 8 t / ha was applied. The specific capacity of the straw in maintaining the phosphorus in the fertilizers in the form accessible to plants was of 1.75 kg P₂O₅/ t straw. In the soils, where the straw and the fertilizers were incorporated together, a synergistic increase of available phosphorus in the arable layer was formed by about three times greater than the amount of phosphorus increases from each type of fertilizer tested separately. The increases of available phosphorus per unit of fertilizer and the synergistic effect of the fertilizing mixtures made of straw and chemical fertilizers were higher when the latter were applied in small dosages. And, on the contrary, where chemical fertilizers were applied in large dosages the increase of the available phosphorus per unit of fertilizer and the synergistic effect were reduced. In combination with straw, low dosages of fertilizers were both agronomic ally and economically more efficient.