Particulate and mineral-associated organic carbon fractions as influenced by corn residue incorporation and simulated tillage

Vegetable production systems rely on frequent tillage to prepare beds and manage weeds. These cultivations disrupt soil aggregates leading to a loss of soil organic carbon (SOC) and decline productivity. Crop residue incorporation could be a way to counteract such negative impacts. This hypothesis was examined using two contrasting soils, a Vertosol and a Chromosol, sweet corn ('Zea mays' var. 'rugosa' L.) residue either incorporated or not and soils sieved/disturbed or not to simulate tillage in an incubation experiment. The treated soils were dispersed and fractionated to determine concentrations of particulate organic carbon (POC) and mineral-associated organic carbon (MOC). POC and MOC were affected by soil type and residue incorporation but not by simulated tillage. Vertosol and '+' residue had significantly higher POC and MOC. On average, the POC and MOC accounted for 23% and 77% of total organic carbon (TOC) for Chromosol and 17% and 83% of TOC for Vertosol, respectively. The limited effect of simulated tillage is possibly due to low intensity and frequency of sieving. The residue amended soils had 15% and 10% higher TOC for Chromosol and Vertosol, respectively. Residue incorporation could help improve SOC in the intensively cultivated vegetable soils. The mineral-associated fraction has a greater SOC stabilising capacity in clayey Vertosols than in sandy Chromosols due to the sorption mechanism of carbon particles on organo-mineral surfaces. Sorption of carbon particles on organo-mineral surfaces may be responsible for the increased MOC in residue amended treatments.