Historical land management alters new soil carbon inputs by annual and perennial bioenergy crops

Bioenergy and bioproduct markets are expanding to meet demand for climate
friendly goods and services. Perennial biomass crops are particularly well
suited for this goal because of their high yields, low input requirements,
and potential to increase soil carbon (C). However, it is unclear how much
C is allocated into belowground pools by perennial bioenergy crops and
whether the belowground benefits vary with nitrogen (N) fertilizer inputs.
Using in situ 13C pulse-chase labeling, we tested whether the
sterile perennial grass Miscanthus × giganteus (miscanthus) or annual
maize transfers more photosynthetic C to belowground pools. The experiment
took place at two sites in Central and Northwest (NW) Iowa with different
management histories and two nitrogen (N) fertilizer rates (0 and 224 kg N
ha-1 yr-1) to determine if the fate of plant-derived soil C depends on
soil fertility and crop type (perennial or annual). Maize allocated a
greater percentage of total new 13C to roots than miscanthus, but
miscanthus had greater new 13C in total and belowground plant biomass. We
found strong interactions between site and most soil measurements –
including new 13C in mineral and particulate soil organic matter (SOM)
pools –which appear to be driven by differences in historical fertilizer
management. The NW Iowa site, with a history of manure inputs, had greater
plant-available nutrients (phosphorus, potassium, and ammonium) in soils,
and resulted in less 13C from miscanthus in SOM pools compared to maize
(approximately 64% less in POM and 70% less in MAOM). In more
nutrient-limited soils (Central site), miscanthus transferred 4.5 times
more 13C than maize to the more stable mineral-associated SOM pool. Our
results suggest that past management, including historical manure inputs
that affect a site’s soil fertility, can influence the net C benefits of
bioenergy crops.