HUMUS CONTENT AND HUMUS FRACTIONS AFTER LONG-TERM SYSTEMIC MINERAL AND ORGANIC-MINERAL FERTILIZATION ON MOLLIC FLUVISOLS

The present work studies the effect of long-term systemic mineral and organic-mineral fertilization on the humus amount, humus type and humus fractions on Mollic fluvisols in Plovdiv region. Fertilizer norms are 1) N75P30K20; 2) N25P15K0 + organic; 3) N50P0K20 and 4) Standard. It was found that long-term systemic mineral and organic-mineral fertilization (forty-seven years) has a stabilized effect on humus content in studied soils. The systemic fertilization lead to a slight decrease of soil humus amount, although the fertilization was excluded since three years. The humus type – was not influenced from the long-term fertilization.