Cattle Manure Application for 12-17 Years Enhanced Depth Distribution of X-Ray Computed Tomography-Derived Soil Pore Characteristics

Long-term manure and inorganic fertilizer application in row crops may significantly influence soil pore characteristics, thereby impacting soil aggregation and structure. Understanding the influence of such soil amendments on soil pore characteristics is useful to develop proper conservation practices. However, there is limited information on the impact of cattle manure and inorganic fertilizer application on soil pore characteristics at a microscale level in the soil profile. Therefore, in this study, the X-ray computed tomography (XCT) technique was utilized to quantify the impact of manure and fertilizer amendments under a corn ( Zea mays L.)-soybean ( Glycine ma x L.)-spring wheat ( Triticum aestivum) rotation system on soil pore characteristics to 40 cm soil depth. The study was conducted at Brookings (initiated in 2008) and Beresford (2003) in South Dakota. The study treatments included: low manure (LM), medium manure (MM), high manure (HM), medium fertilizer (MF), high fertilizer (HF), and control (CK). Four replicated intact cores were collected from all the treatments at 0–10, 10–20, 20–30, and 30–40 cm depths. Image visualization and processing were performed using ImageJ software at a pixel resolution of (0.26 × 0.26 × 0.28) mm 3 . Data showed that treatments by depth interactions were mainly significant for soil organic carbon (SOC) content at 0–20 cm. The HM treatment increased the SOC by 8 to 68% compared to the CK and MF at 0–20 cm for either site. However, treatments did not always impact these parameters beyond 20 cm depth. Considering treatment as the main effect, the MM, HM, and HF increased the total number of pores (TP) compared to the CK at Beresford site. Soil depth impacted the TP and total number of macropores (Tmacro), where more Tmacro was observed at 0–10 cm compared to the 30–40 cm depth at Beresford site. In general, manure application improved SOC and TN contents and soil pore characteristics at 0–20 cm for both sites. This study illustrates the importance of the XCT technique in quantifying soil pore characteristics and highlighted the improvement in the XCT-derived pore characteristic with the long-term application of manure to a greater depth in the soil.