HUMUS STATE OF TYPICAL CHERNOZEMS UNDER CONTINUOUS FERTILIZATION AND IRRIGATION

The content of total humus in chernozems significantly increased under organic or mineral fertilization on a background of manuring. Manurin g provided a rise in the content of humic acids, an increase in the Ch a/Cfa ratio, and a decrease in their optical density. Both in dry farm ing and in irrigated conditions under mineral fertilization, the conte nt of the first and the third fractions of humic acids increased, wher eas the content of the second fraction decreased together with a simul taneous decrease in the Cha/Cfa ratio. Fertilization provided an incre ased content of mobile organic matter and its enrichment in nitrogen a nd phosphorus.