Long-term grass mulching waste recycling and evaluation activation of dissolved organic carbon

This study aimed to clarify that long-term leguminous grass mulching (crown vetch (CV) and white clover (WC)) and gramineous grass (orchardgrass (OG)) drive the distribution of soil aggregates and are associated with dissolved organic matter (DOM) components. Excitation emission spectroscopy and parallel factor analysis (EEM-PARAFAC) were used to evaluate the influence of different grass mulches among aggregates. The results indicated that legumes had a more significant impact on the distribution of aggregates and DOM content than gramineae grass mulching. Leguminous grass mulching significantly increased the proportion of macroaggregates >250 μm (74.65%–83.50%) and aggregates associated with dissolved organic carbon (DOC), especially in microaggregates <250 μm (172.27 mg kg−1 to 391.55 mg kg−1). In addition, leguminous grass mulching (CV and WC) contributed more to the increase in soil total nitrogen (TN) and three identified fluorescent components (UVC humic-like, UVA humic-like and protein-like). The component of UVC humic-like relative abundance decreased (48.66%–36.57%), and the protein-like component increased (21.88%–36.50%) as the aggregate size decreased, but the DOM three compositions did not change. The DOM of macroaggregates had higher aromaticity and lower molecular weight than microaggregates, and the highest abundance of UVC humic-like component (54.52%) was found in the gramineous (OG) large macroaggregates, while the higher abundance of protein-like components (31.07%–36.50%) occurs in leguminous mulching (CV and WC) microaggregates. The results contribute to a further understanding of the dynamic process by which grass mulching mediates aggregate formation and DOM component transformation in semiarid apple orchards under grass waste management.