Changes in soil profile organic carbon and hydro-physical properties as impacted by long-term manure and inorganic fertilizer rates under a corn–soybean rotation system

Using manure appropriately may enhance organic carbon and hydro-physical properties while avoiding the negative impact on the environment. However, how manure impacts soils, especially at lower depths, is still not well studied. Therefore, the objective of this study was to assess the impact of different manure and inorganic fertilizer application rates on soil profile organic carbon and hydro-physical properties under corn (Zea mays L.)–soybean (Glycine max L.)–spring wheat (Triticum aestivum L.) rotation at Beresford (established in 2003) and Brookings (established in 2008) sites in South Dakota. The treatments included low manure (LM), medium manure (MM), high manure (HM), medium fertilizer (MF), high fertilizer (HF), and control (CK). Four replicated intact soil cores were collected from all the treatments at 0- to 10-cm, 10- to 20-cm, 20- to 30-cm, and 30- to 40-cm depths. Considering treatments by depth interactions, the LM and MM decreased bulk density (ρ_b) by 6.9%–22.1%, as compared to the CK at 0–30 cm for either site. The HM decreased ρ_b by 16.4%–24.7%, as compared to the HF at 30–40 cm for either site. On observing treatment as the main effect, the MM and HM increased the soil water retention (SWR) at 0 and −5 kPa compared to MF, HF, and CK in Brookings, and the MM increased the SWR at −30 kPa as compared to the MF in Beresford at 0- to 40-cm depths. The data suggest that continuous manure application may enhance organic carbon and hydro-physical properties at lower depths. Therefore, this study concluded that long-term manure application showed greater improvements when compared to long-term application of inorganic fertilizer alone. It can improve hydro-physical properties, thereby stabilizing the soil structure and improving water retention at lower depths.