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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. |
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