On the clayey-loam low-eroded common chernozem from the Republic of Moldova, village Ursoaia, Cahul district, at the IPAPS Dimo Experimental Station, the fresh straw spread during threshing was investigated as a fertilizer for seven years. During this research, the phenomenon of annual humus content loss by mineralization in the arable layer of cultivated chernozems without fertilizers, with 640 kg/ha, was confirmed. Unfermented straws incorporated separately without other fertilizers have helped to protect soil against humus loss and even has contributed to partial straw humification. Soil humus mineralization in the soil treated with 4 t/ha of straw was seven times lower than at untreated soil. One tonne of straw save 484 kg of humus from mineralization. Up to 10 percent of the organic matter from separately applied straw was humidified. The phenomenon of straw humification intensification when it is combined with chemical or organic fertilizers has been demonstrated. The humus content increase was in direct proportion to the applied straw dose and the chemical fertilizer dose used with the straws application. Humus specific growth In the case of straw application combined with chemical fertilizers is ranged between 150 and 360 kg of humus per tonne of straw, so 17-40 percent of straw organic matter was humidified.