Effective carbon sequestration in Italian agricultural soils by in situ polymerization of soil organic matter under biomimetic photocatalysis

Facing an exploding population growth with consequent increase of agriculture intensification, new chemical technologies are being sought to limit organic matter losses and reduce land degradation. Here, we report that an effective organic carbon sequestration in different cropped soils of Italy is obtained by an in situ photo-oxidative coupling among soil humic molecules, when catalyzed under solar irradiation by a water-soluble biomimetic iron-porphyrin catalyst amended to field soils. A 3-year long field study showed that the catalyst-assisted in situ photochemical polymerization of humic matter enabled a yearly sequestration of soil organic carbon that ranged from 2.2 to 3.9 t ha-1y-1, despite the periodical soil disturbance due to a conventional tillage management. This significant stabilization of organic matter was observed not only in bulk soils but also in water-stable aggregates, whose loss of organic carbon during separation was limited in catalyst-treated soils. Although crop yields were the same in treated and control soils, measurements of phospholipids fatty acids and soil enzyme activities indicated that the catalyzed in situ photo-oxidative coupling of humic molecules did not alter the structure and activity of microbial communities and the biological functions of soils. This innovative and ecologically safe catalytic technology may be developed as a useful soil management practice to stabilize organic matter in situ in arable soils, while concomitantly ensuring soil functions and sustainability of crop production.