Curve-fitting techniques improve the mid-infrared analysis of soil organic carbon: a case study for Brookston clay loam particle-size fractions
Citation
Fan, R., Yang, X., Drury, C.F., Zhang, Z. (2018). Curve-fitting techniques improve the mid-infrared analysis of soil organic carbon: a case study for Brookston clay loam particle-size fractions. Scientific Reports, [online] 8(1), http://dx.doi.org/10.1038/s41598-018-30704-2
Plain language summary
Few studies have evaluated structural features of soil organic carbon in different soil particle size
fractions, especially the changes of soil organic carbon caused by tillage, using Fourier transformed mid-infrared (MIR) spectroscopy. To make a contribution in this context, authors collected soil samples from a Brookston clay loam which had been under short-term (13 yr) and long-term (27 yr) of mouldboard plow and no-tillage managed corn-soybean rotation, and the samples were separated into sand, silt, and clay fractions based on the size of particles. Structural features of SOC in these soil fractions were investigated using curve-fitting analysis of mid-infrared (MIR) spectra. Stable carbon content was found to be greater in clay- than in sand-sized fractions, while labile carbon content was higher in sand- than in silt- and clay-sized particles. With decrease in tillage intensity, the labile carbon gradually increased in sand- and clay-sized fractions but not in the silt-sized fraction. The labile carbon in sand fraction was significantly greater in long-term no-tillage than long-term mouldboard plow soil. The labile carbon in silt- and clay-sized fractions was greater in long-term no-tillage than in both long-term and short-term mouldboard plow soils, whereas stable carbon contents were higher in both mouldboard plowed soils than in long-term no-tillage soil. These findings were well demonstrated with the curve-fitting technique, and the results indicate that the curve-fitting of mid-infrared spectra advances the analysis of organic matter in soil samples.
Abstract
Few studies have evaluated structural features of soil organic carbon (SOC) in different soil particle fractions, especially SOC changes induced by tillage, using Fourier transformed mid-infrared (MIR) spectroscopy. To make a contribution in this context, soil samples of a Brookston clay loam (mesic Typic Argiaquoll) with averaged pH and organic matter concentration at 7.28 and 43.9 g kg−1, respectively, were collected from short-term no-tillage (NT97) and mouldboard plow (CT97) treatments initiated in 1997 and long-term no-tillage (NT83) and mouldboard plow (CT83) treatments initiated in 1983 under a corn-soybean rotation, and were separated into sand, silt, and clay fractions using sonication. Structural features of SOC in these soil fractions were investigated using curve-fitting analysis of mid-infrared (MIR) spectra. Aromatic C content was found to be greater in clay- than in sand-sized fractions, while aliphatic C content was higher in sand- than in silt- and clay-sized particles. With decrease in tillage intensity, the aliphatic C gradually increased in sand- and clay-sized fractions but not in the silt-sized fraction. The aliphatic C content in sand fraction was significantly greater in NT83 than CT83 (P < 0.05). The aromatic C in silt- and clay-sized fractions was greater in NT83 than in both CT soils, whereas aromatic C contents were higher in both CT soils than in NT83 soil. Significantly higher aromatic/aliphatic C ratio in CT83 than NT83 was found in sand-sized fractions, while the opposite trend was found in the silt-sized fraction. These findings were not apparent until the curve-fitting technique was employed, which has the capacity to quantify many overlapped bands in the spectra. This study demonstrates that the curve-fitting of MIR spectra advances the analysis of organic matter in soil samples.