Soil Science Society of America Journal · 2008 · 374 citations · 32 references
AgricultureEarth SciencesSoil SciencesSoil BiogeochemistrySoil Organic MatterSoil ScienceCarbon SequestrationManure Nutrient ManagementSoil Carbon ChemistrySoil Carbon FractionationSoil Organic Matter FractionsVariable Rate Manure ApplicationLabile Carbon PoolsManure Application RatesOrganic Nutrient PoolsSoil Carbon PoolsSoil Carbon SaturationSoil Labile CarbonSoil Organic Carbon PoolsStable Carbon Pools
Soil organic carbon does not always increase linearly with added carbon, limiting the rate and efficiency of its stabilization. The study tests whether a long‑term manure application regime induces carbon saturation and whether different soil carbon pools saturate at distinct rates. SOC pools were isolated by physical fractionation from a Lethbridge, Canada experiment where manure has been applied since 1973 at 0, 60, 120, and 180 Mg ha⁻¹ yr⁻¹. SOC in mineral soil, small macroaggregates, microaggregates, and silt‑plus‑clay increased up to 120 Mg ha⁻¹ yr⁻¹ but plateaued at 180 Mg ha⁻¹ yr⁻¹, indicating saturation, while only large macroaggregates continued to accumulate carbon—primarily coarse particulate organic matter—yet their turnover rose, so additional carbon input ultimately accumulates only in rapidly turning‑over labile pools.
Recently, it has been suggested that soil organic C (SOC) does not always respond linearly to increasing C input, thereby limiting the rate and efficiency of C stabilization in soils. Therefore, we postulated that when a soil is exposed to a broad range of C inputs through a range of manure treatments, it will show C saturation behavior and different SOC pools will saturate at different rates. To test this, different SOC pools were isolated by physical fractionation techniques from a long‐term agricultural experiment in Lethbridge, Canada. In this experiment, manure has been applied since 1973 at rates of 0, 60, 120, and 180 Mg ha −1 yr −1 (wet weight). In the total mineral soil as well as the small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and the silt plus clay fraction (<53 μm), an increase was observed in SOC contents with an increase in manure application rate to 120 Mg ha −1 yr −1 However, no additional C was sequestered when the manure application rate was augmented to 180 Mg ha −1 yr −1 , indicating C saturation in these SOC pools. Large macroaggregates (>2000 μm) were the only water‐stable aggregate fraction that increased in C content across all manure input levels. Further physical separation of macroaggregates into subpools by microaggregate isolation showed that coarse (>250 μm) particulate organic matter (POM) was the fraction that accounted most for the increase in C content of the large macroaggregates. Furthermore, the turnover of large macroaggregates increased with increasing manure applications, as indicated by decreased formation and stabilization of intramicroaggregate POM within the large macroaggregates. We conclude that as C input increases, the mineral fraction of a soil saturates and consequently additional C input will only accumulate in labile soil C pools that have a relatively faster turnover.
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Organic matter and water‐stable aggregates in soils
J. M. Tisdall, JM Oades · Journal of Soil Science · 1982 · 6.2K citations
Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils
Johan Six, Richard T. Conant, E. A. Paul et al. · Plant and Soil · 2002 · 4.4K citations