||In 1999 a one factor field experiment with spring barley, oat and potato was carried out at Sicienko (Kujawy and Pomerania Province), on the land of the Testing Station of Agriculture Department of Technical and Agricultural Academy. For the experiment a fertilizer named SONATA M - Mg obtained from the sludge according to the patent application no. P.326127 was used. The fertilizer subjected to the investigation is mineral-organic with the addition of the micronutrients in form of chelate (derivative of ethylenediamineteraacetic acid, EDTA) of the following contents: Mg - 10%, organic parts 5-10%, Cu - 0.16%, Mo - 0.03%, Mn - 0.7%, Zn - 0.2%. In the experiment, five fertilized objects were determined with different doses and fonns of nitrogenous fertilizers, and the tested fertilizer Sonata M - Mg was used in two doses: 3 and 5 kg-ha"1. The results of the conducted tests of the exact field experiments showed, in the year of the experiment, a very clear effect of the used doses of ammonium nitrate under the particular plants, as well as they indicated a clearly positive influence of the addition of Sonata M - Mg to the saltpetre. The efficiency of the applied doses is high and also the sole effect of Sonata in relation to the saltpetre is significant. A strong effect of the tested fertilizer on the qualitative features of the crop was also observed.