Study was conducted in long-term field experiment (47 years) in irrigated vegetables cropping system on chernozem heavy loamy in Forest-Steppe zone of Ukraine. Different types of fertilization regimes were compared: mineral (NPK); organic (manure) and organo-mineral (manure + NPK). Humus content decreased by 10-12% after two 9-crops rotations compared to initial data (before irrigation) on all variants of experiment. Since the end of third 9 years cropping system humus has been increased up to 4.35% at the end of fifth crop rotation in organo-mineral fertilization regime. Mineral fertilization systems did not increase humus content compared to the control (without any fertilization). The highest humic compounds content in chernozem was observed on organic fertilization system. Long-term regular manure application led to significant increase of the content of humic complexes with calcium in comparison with mineral and organo-mineral fertilization regimes. Fulvic acids content was higher on variant with NPK application.
KUTOVA et al. (Tue,) studied this question.