Evidence is accumulating that belowground crop residues contribute more efficiently to the build‐up and maintenance of native soil organic carbon (SOC) than aboveground plant parts. We corroborated previous testing of the hypothesis that root‐C would preferentially accumulate in soil microaggregates, where it is physically protected against microbially mediated decomposition. In three European field trials with C3 to C4 crop transitions, we compared the content of maize‐C (Zea mays L.) in soil from rotations with grain maize (MG) or silage maize (MS) (i.e. with incorporation of roots and shoots or roots only). After decades of maize cultivation, SOC content did not differ within three out of four MG–MS pairs, although obviously larger amounts of shoot biomass were added to soil in the case of MG. We found that relative contribution of roots was on average 3.5 times more than shoots to the build‐up of SOC per equivalent mass of residue C added to soils. Preferential occlusion of root‐C as silt‐sized intra‐microaggregate particulate organic matter (iPOM) was not observed. There were much larger effects from shoot incorporation on maize‐C in the >53‐μm fraction and free silt and clay. Storage of root‐C as sand‐sized iPOM was not quantified here, but first estimates suggested that physical entrapment at this level could only partly explain the longevity of root‐C in soil. We reconfirm the relative stability of root‐C in soil, but do not conclude that this stems from preferential physical entrapment over shoot‐C. Future work should investigate the cause of preferential root‐C association with the clay‐sized fraction and if this occurs before or after microbial processing.
Highlights
The hypothesized preferential physical stabilization of root‐C was assessed.
Aboveground biomass had a minor effect on SOC storage in European long‐term trials.
Contribution of maize root‐C to maintenance of SOC was three‐fold that of shoot‐C inputs.
There was no preferential occlusion of root‐C in silt‐sized microaggregates.
Living Labs, which are urban sites that include households and workplaces and are used to study the real-time use of technological innovations and devices, have become increasingly popular among environmental scientists to gain insights into energy consumption in peoples’ everyday life. However, recruiting a viable number of participants for such studies can pose a challenge to researchers: Factors like month-long study durations and the requirements to handle smart technology proficiently or frequently exchange information with researchers and other users do not necessarily make participation attractive for everyone. To identify relevant factors for participation, we conducted three large preregistered surveys (total N = 1479) in Austria: two conjoint studies and one experimental study. We found that advertising a Living Lab with a shorter duration (less than a month), providing the option to participate from home, and—a crucial point—offering financial incentives should be considered when considering promotion strategies and conducting thorough study planning. However, we discuss the fact that there might be a risk of selection bias for technic-savvy and future-oriented people.
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