Effect of Nature of Fertilizer on Humic Substances in Vertisol

The stable reserves of humus in soils owe their origin primarily to humic acids and humins. The general principle follows that for accumulation of humus in soils it does not suffice to add additional quantities of organic matter in the form of plant residue, manure or other organic material. Simultaneous with such application, conditions must be created that ensure complete humification of organic compounds that is their conversion mostly in to humic acids or humin. Evidences are available that soil organic matter levels increased markedly in plots receiving farm yard manure and long term continued use of inorganic fertilizers containing N, P, K and Mg has increased organic matter levels. Hence this investigation was taken up to evaluate the effect of long term organic and inorganic additions on content of humic substances on Vertisols to study the effect of applied fertilizer nutrients on organic carbon content and content of humic acid, fulvic acid and humin + nonhumic matter. The results revealed that balanced NPK through inorganic sources significantly increased the organic carbon, humic acid, fulvic acid, humin + nonhumic matter and mineralizable nitrogen status in soil.