Indicator-based assessment of mineralization–synthesis of organic matter in soil under contrasting crop fertilization regimes

The study examines the directionality of mineralization–synthesis processes of soil organic matter under contrasting crop fertilization regimes. Given the close interdependence of the carbon and nitrogen cycles, the dynamics of N 2 O and CO 2 emissions were assessed in a long-term field experiment on leached chernozem soil within a short-rotation system of potatoes, spring barley, peas, and winter wheat. Application of 40 t/ha of farmyard manure markedly distinctly mineralization during the first year, followed by a gradual decline in subsequent years. Continuous use of mineral fertilizers alone intensified mineralization, with further increases at higher nitrogen rates. In contrast, low mineral fertilizer rates (≤ N 40 P 40 K 40 ), combined with the direct and residual effects of straw and lupine green manure, promoted synthetic processes. Medium doses (N 60 P 60 K 60 – N 80 P 80 K 80 ) applied on an organic background resulted in a balanced dynamic between mineralization and synthesis. At high doses (N 90 P 90 K 90 – N 120 P 120 K 120 ), the addition of straw and green manure reduced N–N 2 O and C–CO 2 losses compared with mineral-only treatments; nevertheless, mineralization remained the prevailing process. • Directionality of mineralization–synthesis of OM in soil was assessed using the N–N 2 O:C–CO 2 emission ratio. • Incorporation of winter wheat straw and lupine green manure enhanced synthetic processes in leached chernozem. • Use of mineral fertilizer intensified mineralization in proportion to application rates. • Combining mineral fertilizers with straw and green manure improved the mineralization–synthesis balance of OM in soil. • Evaluating biological process directionality enables rapid identification of effective integrated fertilization strategies.