Soil Organic Carbon Accumulation under Different Forms of Organo-Mineral Fertilizers and Methods of Their Application on Ukrainian Black Soil

Soil organic carbon management is a key element in solving such urgent global-scale challenges as overcoming degradation of soils and mitigating climate change. Organic fertilizers application has a significant potential for sequestering C in soils, but their efficiency depends on decomposition characteristics. Firstly, it noted the dependence of resynthesis of humic compounds in a soil on a quality of organic inputs, secondly - a need for zonal approach to fertilizers production based on amphiphile properties of macromolecules.

The present study was conducted in long-term field experiment on black soil in Forrest-Steppe zone of Ukraine. The technology of production of organo-mineral fertilizers (OMFs) was based on the regulated processing of livestock waste with mineral components to stabilize it with hydrophobic bonds. OMFs in amorphous and granular form were compared in case of broadcast and band method of incorporation. The dose of OMF input was equivalent 350 C kg ha^-1 and 80 N, 80 P, 80 K kg ha^-1. Organic carbon content in soil was determined by Turin method. Different organic matter fractions were isolated: humic acids (HA), fulvic acids (FA), and humin.

The soil C accumulation rates in OMF treatment was by 15 % higher than in manure treatment and up to 70 % higher than in chemical fertilizer treatment, respectively. The soil C accumulation was strongly influenced by the form of OMF and method of their application. The highest TOC level was found over band application of amorphous OMF, accumulating 6.2 t C ha^–1 yr^–1 in 0-20 cm soil layer. Lower efficiency of broadcast incorporation OMFs could be explained by more intensive mineralization due to higher aeration. Taking into account the effect of OMFs on C stock an advantage of amorphous form versus granulated OMF with similar composition was proven. Black soil on control plot (without fertilization) had almost equal ratio between HA, FA and humin in humus composition. The content of humic compound increased in all treatments. Applying OMF significantly increased HA content in black soil compared to applying mineral fertilizer. OMFs application promoted the increase of the degree of condensation of organic matter. The highest HA/FA was found under the effect of broadcast incorporation OMF. That means that low molecular weight compounds were rapidly degraded while more resistant to mineralization HA were formed in soil. There was no significant difference in humus composition between amorphous and granulated OMF.