Long-term raw crop residue but not burned residue incorporation improved soil multifunctionality in semi-arid agroecosystems

Globally, topsoil in most agroecosystems is being increasingly eroded by intensive land use practices. In semi-arid regions, restoring topsoil is particularly an important cue to optimize soil multifunctionality, as the loss of soil organic carbon (SOC) is often accompanied by the loss of soil fertility. Here, we test the additive effects of different crop residue incorporation regimes on topsoil multifunctionality in a decade long field experiment on a maize-maize-potato cropping system. In each year, crop residues of a double maize rotation (Spring-Summer) were exposed to three contrasting managements, i.e., no residue incorporation (NRI), burnt residue incorporation (BRI) and raw residue incorporation (RRI), before planting a potato crop in the Fall. Our results showed a proportional increase in SOC stocks of up to 49–69% for RRI compared to BRI and NRI, respectively. Similarly, RRI also contributed to greater qualitative C stocks, such as particulate (PAOC) by 74–86% and mineral (MAOC) associated organic carbon by 63–107% than BRI and RRI. In contrast, BRI showed no discernible change in organic C stocks, but a significant destabilizing effect on soil pH, electrical conductivity (EC), and bulk density (BD). The water extractable organic carbon (WEOC) and the C-lability index were significantly reduced in BRI plots and consequently curtailed soil microbial activity and microbial biomass synthesis. Interestingly, BRI showed a decrease in P-acquiring enzymes compared to C- and N-cycling enzymes, possibly reflecting the different demand of soil microbes for different nutrients. In contrast, an ensured availability of C substrate by RRI significantly increased the population of cultivable microflora (e.g., bacteria, fungi, actinomycetes). Above all, RRI was very effective in improving soil ecosystem multifunctionality, as evidenced by improved soil structural stability due to greater C accumulation and stabilization, resulting in enhanced NPK availability, although the low soil structural stability index (SSI ≤ 3%) still highlights the pervasive risk of land degradation.