Principal Component Analysis for the Quantification of Soil Horizon Carbon Stocks in Relation to Soil Bulk Density

Abstract

Accurate quantification of the changes in carbon stocks of different horizons of the soil profile pit in relation to soil bulk density is a prerequisite to understand the role of soil in the global carbon cycling and climate change mitigation. This paper seeks to draw attention to the carbon storage capacity of the individual soil horizon with particular emphasis on soil bulk density. Three (3) profile pits were dug at equal distance of 100 meters. These profile pits were carefully sampled and analysed in the laboratory using standard methods. Soil data were subjected to principal component analysis (PCA), regression and coefficient of variation analyses using SPSS. Results showed that A, Ap, AB and Bt were the soil horizons identified in the three different soil profiles at the time of sampling. Bulk density values ranged from 1.43 -1.66 g cm -3 (mean = 1.49 g cm -3 ) in profile pit 1, 1.43 -1.62 g cm -3 (mean = 1.53 g cm -3 ) in profile pit 2 and 1.15 -1.64 g cm -3 (mean = 1.40 g cm -3 ) in profile pit 3 respectively. In profile 1, 2 and 3, the average carbon stock ranged from 4500.6, 3791.67 and 3689.2 g C m -2 respectively. From the PCA results, four variables were observed, they include organic carbon, inorganic carbon, water stable aggregate and carbon stock. The first PC (PC1 = organic carbon) had a value of 0.968, PC2 (inorganic carbon) = 0.968, PC3 (water stable aggregate) = 0.874 and PC4 (carbon stock) = 0.844, indicating positive effects. From the PC plot, the eigenvalues are 3.57, 3.08, 1.78 and 1.10. However, the first PC explains 32.47 % of total variation whiles the second, third and fourth PCs explain 60.47, 76.67 and 86.72 % respectively.Contribution/Originality: This study contributed substantially to the effective understanding of carbon accumulation in soil in relation to soil compaction; hence, for the comprehension of the exact quantity of carbon accumulated in the soil, accurate measurement of the amount of carbon sequestered by individual natural horizon of the soil profile is imperative. INTRODUCTIONAccurate and effective determination of bulk density is indispensable in monitoring soil carbon stocks and soil carbon stock variations in the soil profile pit. The result of soil carbon stock is conventionally expressed in units such as percentage (%), milligram of carbon per kilogram of soil (mg C kg -1 ) or microgram of carbon per kilogram of soil (g C kg -1 ) (Powlson, Whitmore, & Goulding, 2011). These are units of concentration, though they are often