Crop-weed competition changes the decomposition of soil organic matter fractions in the rhizosphere

Certain plant combinations can stimulate the mineralization of soil organic matter (SOM), thereby changing the storage of soil organic carbon and affecting the physical and chemical soil properties. The aim of this study was to evaluate whether competition between weeds and maize can stimulate SOM decomposition. Eight treatments were performed: monoculture of maize and weeds (<i>Amaranthus viridis, Bidens pilosa</i>, and <i>Ipomoea grandifolia</i>), maize in competition with weeds, and non-cultivated soil. During cultivation, the rhizosphere priming effect (RPE) on SOM was estimated. Additionally, at 60 days after planting, soil samples were collected to measure the C contents of particulate (POM) and mineral-associated (MAOM) organic matter. From the 43^rd day of cultivation onwards, the coexistence between maize and <i>B. pilosa</i> led to the highest RPE values, while maize vs. <i>A. viridis</i> showed negative RPE. Maize vs. <i>A. viridis</i> and maize vs. <i>I. grandifolia</i> caused increase in MAOM-C and decreases in POM-C. <i>Ipomoea grandifolia</i> monoculture and maize vs. <i>B. pilosa</i> led to the highest MAOM-C losses and reduced POM-C compared to the non-cultivated soils. Here it is demonstrated that competition between maize and <i>B. pilosa</i> increases SOM mineralization, while competition between maize and <i>A. viridis</i> or <i>I. grandifolia</i> retards this process.