Role of silt and clay fractions in organic carbon and nitrogen stabilization in soils of some old fruit orchards in the Nile floodplain, Sohag Governorate, Egypt

Abstract

Abstract Purpose Study the effect of both silt and clay fractions on stabilizing organic carbon and total nitrogen in soils of some old cultivated fruit orchards in Sohag, Egypt. Methods Eleven surface soil samples (0–15 cm) were collected. Silt (63–2 μm) and clay (< 2 μm) fractions were separated from soils and analyzed for cation exchange capacity (CEC), organic carbon (OC), total nitrogen (TN), specific surface area (SSA), X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopic analysis were determined using the standard analysis methods. Results The silt and clay were responsible for 77.49 to 93.34% of soil CEC. The SSA of clay was twice the silt, and the phyllosilicates (%) average was 29.83% and 62.70% in silt and clay. Other minerals, such as quartz, feldspar, and carbonate minerals, were detected in these fractions. The phyllosilicate species of clay were smectite-illite mixed layers (44.4–88.9%), Smectite (1.0–6.4% except one sample recorded 45.7%), Kaolinite (3.7–10.5%) and kaolinite/smectite mixed layers (2.0–8.2%). The average OC-silt and clay were 6.79 and 8.96 g OC kg−1 soil (38.01 and 50.28% of soil OC). On average, the total nitrogen (TN) in silt and clay particles was 0.817 and 1.156 g N kg−1 soil (35.88 and 50.66% of soil TN). The OC and N content significantly and positively correlated with CEC, SSA, and phyllosilicates in the fine fractions. Conclusion Results showed that the soil's capacity to sequester OC and N is affected significantly by its fine particles' content, characteristics, and mineralogy.