Abstract
It has been shown the role of carbon of dissolved organic matter (C DOM) in humus composition of irrigated chernozems as well as participation of humus substances proper in the formation of DOM. It has been found out that in chernozem long-term irrigated with weakly alkaline water the yield of C DOM is reliably higher than in nonirrigated soil when used even ordinary water extraction. It accounts for 53 and 40 mg l–1 respectively. It is attributed to the fact that because of influence of irrigative water the pH range became wider to some extent and alkalinity of soil medium became stronger and consequently the solubility of DOM increased. It has been noted that that the same tendency that is decrease is observed in depthwise distribution of humus and C DOM. As it should be expected, in irrigated soil processed with irrigative water the content of C DOM is somewhat higher (by 7–10 mg l–1) in the studied part of the profile as a whole. At the same time the relative role of C DOM in humus composition increases with increasing pH, up to 3 % of total organic soil carbon. It has been examined the interaction of irrigative water free of DOM with preparations of humus acids extracted from soil. Drown coloration of irrigative water is evidence of separation of DOM from humus acids. Moreover, the yield of C DOM proved to be three times higher in case of irrigative water than distilled one and accounted 120 and 350 mg l–1 respectively. This comparative experiment is an evidence of the fact that humus acids
 can be served as a source of DOM, especially in the event if more accessible organic matter is not available. Thus, long-term irrigation of chernozems in case of unsatisfactory application of organic fertilizers leads not only to biological and irrigational humus losses but also humus losses by way of transformation of humus acids into DOM
Published Version
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