The Relationship between Carbon Input, Aggregation, and Soil Organic Carbon Stabilization in Sustainable Cropping Systems

Abstract

One of our current challenges is to quantify the mechanisms, capacity, and longevity of C stabilization in agricultural lands. The objectives of this study were to evaluate the long‐term (10 yr) role of C input in soil organic carbon (SOC) sequestration and to identify underlying mechanisms of C stabilization in soils. Carbon input and SOC sequestration, as governed by crop management strategies, were assessed across 10 Mediterranean cropping systems. Empirically derived relationships between yield and aboveground plus belowground crop biomass as well as estimates of C contributions from crop residues and manure amendments were used to quantify cumulative C inputs into each cropping system. Soil samples were separated into four aggregate size classes (>2000, 250–2000, 53–250, and <53 μm) and into three soil organic matter (SOM) fractions within the large (>2000 μm) and small (250–2000 μm) macroaggregates. Aggregate stability increased linearly with both C input (r2 = 0.75, p = 0.001) and SOC (r2 = 0.63, p = 0.006). Across the 10 cropping systems, annual soil C sequestration rates ranged from −0.35 to 0.56 Mg C ha−1 yr−1 We found a strong linear relationship (r2 = 0.70, p = 0.003) between SOC sequestration and cumulative C input, with a residue‐C conversion to SOC rate of 7.6%. This linear relationship suggests that these soils have not reached an upper limit of C sequestration (i.e., not C saturated). In addition, C shifted from the <53‐μm fraction in low C input systems to the large and small macroaggregates in high C input systems. A majority of the accumulation of SOC due to additional C inputs was preferentially sequestered in the microaggregates‐within‐small‐macroaggregates (mM). Hence, the mM fraction is an ideal indicator for C sequestration potential in sustainable agroecosystems.

Effect of Long-Term Application of Inorganic and Organics on Soil Aggregate Fractions in Double Rice Cropping System

“…This indicated that smaller particles with greater surface area may be responsible for scavenging a sizable amount of C in micro aggregates. Kong et al, (2005) and Majumder et al, (2007) also reported similar results. However, there was a little influence of increasing C inputs was observed for C associated with aggregates of 250-1000 and < 53 µm size.…”

“…A higher surface area for smaller particles may be responsible for this. Christensen (1986) and Kong et al, (2005) also reported similar results. Gupta Choudhury (2011) and Datta (2016) also reported similar findings in Indian subcontinent.…”

“…The aggregation is a means to both protect and conserve soil organic carbon (SOC) and allow the stored organic matter to function as a reservoir of plant nutrients. Crop cultivation is known to adversely affect the distribution and stability of soil aggregates and reduces SOC stock in soils (Six et al, 2000;Kong et al, 2005). The impacts of cultivation on C stock have commonly been observed to be restricted mostly to surface soils and/or to root zone depth (Paustian et al, 1997b).…”

Greenhouse gas emissions from conventional and organic cropping systems in Spain. I. Herbaceous crops

“…Using the same source, the absence of some kind of N input in herbaceous systems was associated to a net emission of 0.48 Mg C per hectare. We considered that 8.5 % of straw C was incorporated into the soil at a 100-year time horizon using data from other studies under Mediterranean conditions (Alvaro-Fuentes and Paustian 2011; Kong et al 2005). Organic farms usually produce more weed biomass than conventional ones (Guzmán et al 2014).…”

Effect of Long-Term Double Rice Cultivation with Different Management Practices on C Sequestration and Economics under Hot Semi-Arid Climate in India

“…Crop cultivation is known to adversely affect the distribution and stability of soil aggregates and reduces SOC stock in soils (Kong et al, 2005). The impacts of cultivation on C stock have commonly been observed to be restricted mostly to surface soils and/or to root zone depth (Paustian et al, 1997b).…”