Extracted samples and in situ soil investigations to assess the effects of different land use and tillage management practices on soil organic matter composition

The effects of land use change on soil organic carbon (SOC) content have been investigated extensively. However, little research has been conducted on how soil organic matter (SOM) chemistry changes under different land use management practices, particularly with different soil cultivation methods. Thus, in this study, we compared the effects of various land use management practices, including six medium‐term tillage practices, namely no‐tillage (zero‐tillage), disking, shallow cultivation, deep cultivation, ploughing, and loosening, and a natural ecosystem, namely tree line, on SOM composition. The present study examined Chernozem soils during spring and autumn under varying land uses in randomised complete block designs, with four replicates at depth increments of 0–10 cm. The SOM composition was characterised using diffuse reflectance infrared Fourier transformat spectroscopy (DRIFTS) and ultraviolet–visible spectroscopy (UV‐VIS). More intensive tillage operations resulted in larger SOM composition changes. Overall, conservation tillage, namely no‐tillage, disking, shallow cultivation, and deep cultivation, SOM was more like the tree line soil than the soil under conventional tillage. Both DRIFTS and UV‐VIS revealed that tree line soil had the lowest aromaticity (15%) and, therefore, a lower decomposition rate and higher SOM recalcitrance compared with the cropland soil (27%). After observing the relationship between tillage operation and aromaticity, aromaticity increased with increasing tillage intensity. This study demonstrates that land use can alter the structure and stability of SOM compounds. We observed that afforestation is similar to conservation tillage, and results are obtained quickly (<40 years). Hence, regeneration agriculture and conservation tillage may be the superior solutions for increasing SOM, sustainable agriculture, and food security in current soil and climate conditions. In addition, DRIFTS measurements of bulk soil provided more detailed information on the quality and stability of SOM than UV‐VIS measurements.