Residue incorporation and organic fertilisation improve carbon and nitrogen turnover and stabilisation in maize monocropping

Residue incorporation and organic fertilisation are recommended to increase soil organic matter (SOM) content, thus promoting the provision of multiple ecosystem services. However, the positive effect of crop residue on SOM is often considered rather low, thus requiring a deeper knowledge of their management. In addition, organic fertilisation is thought to be less efficient than mineral. In this context, it is important to understand the response of SOM pools to long-term crop residue incorporation and organic fertilisation and their effect on nutrient cycling and on feed production, in order to judge the sustainability of these practices. We carried out an in-depth multidisciplinary survey to investigate the effect of 28 years of residue incorporation combined with three different nitrogen (N) fertilisation strategies (manure, slurry and mineral) on density fractionated SOM pools differing for their turnover time, and on soil enzymatic activity in a monocropping maize system in NW Italy. Results showed that in the long-term crop production was not altered by organic fertilisation. Organic fertilisation in combination with residue incorporation led to the highest total organic C and total N content down to 90 cm, which was reflected in each SOM pool. In addition, regular applications of crop residue and manures markedly increased C- and N-degrading enzymes, thus enhancing the turnover rates of C and N. We conclude that combining crop residue with organic fertilisation enhanced the provision of regulating services and soil activity, and is a valid approach for maintaining sustainable production in agroecosystems. • Mineral fertiliser N and removal of maize residues deplete SOM and enzyme activities down to 90 cm depth. • Crop residues incorporation and organic fertilisation significantly affect soil TOC and TN contents down to 90 cm depth. • Both practices increase in particular the mineral-associated fraction of TOC and TN. • Organic fertilisation increases stable SOM to a greater depth than crop residues. • Organic fertilisation fosters C- and N- degrading enzyme activities more than crop residues.