High surface area inorganic minerals show promise in protecting carbon from soil organic amendments

Protecting soil organic compounds could assist with global efforts to mitigate climate change, as well as improve soil health. Recent research has indicated that high surface area inorganic minerals (HSAIMs) can protect soil organic matter (OM). We evaluated if adding HSAIMs to soils can protect carbon from common organic inputs added to fallow soils prior to planting. Four added HSAIMs were investigated - two manufactured zeolites, one natural zeolite and bentonite clay - along with a carbon-rich (peat moss) and carbon-poor (composted cow manure) OM source. The added HSAIMs and organic sources were incorporated into a microbially active (clayey Vertisol) and inactive (sandy Arenosol) soil at application rates of 20 tonnes.ha-1 for the minerals and 60 tonnes. ha-1 for the organics. The treatments were incubated for three months under laboratory conditions and were subjected to continuous wetting-drying cycles. Peat moss resulted in higher organic carbon (Corg) and OM losses than cow manure. Moreover, the addition of HSAIMs to the Peat Moss+Arenosol treatments appeared to slightly enhance these losses, albeit not significantly (p>0.05). Carbon/nitrogen (C/N) ratios revealed that the Arenosol treatments were depleting soil N to access the carbon provided by the peat moss. For all other treatment combinations, the addition of HSAIMs promoted greater retention of Corg (p<0.05 in one treatment combination) and OM (p<0.05 in four treatment combinations), relative to the controls. Modelling carbon balances using OM data was more effective than using direct Corg values, due to strong Corg measurement variance. Modelled Corg data revealed the added HSAIMs achieved up to 25 % carbon protection, with the manufactured zeolites particularly effective. The study shows promise for added HSAIMs to protect carbon released from decomposing organic amendments added to fallow soils. However, addition of these minerals to N-limited soils receiving carbon-rich amendments might accelerate carbon losses.