Differences in soil physical properties caused by applying three organic amendments to loamy clay soil under field conditions

PURPOSE: Organic amendment applications have been proposed as important agricultural management practices for the maintenance of soil health. Weathered coal (WC), biochar (BC), and grass peat (GP) have been used widely and globally for a long time. However, the differences in soil physical properties following the application of these amendments have rarely been evaluated under the same field conditions. METHODS: In this study, the changes in the physical properties of loamy clay soil after applying WC, BC, and GP (3%, w:w) were investigated under field conditions after 375 days. RESULTS: Relative to unamended soil, the WC, BC, and GP applications increased the total porosity and decreased the bulk density of amended soils (P < 0.05). The soil water content increased by 23.8% following the BC application, whereas it was decreased by 10.5% following the GP application (P < 0.05). The application of all the amendments increased the soil average temperature by 0.71 °C (GP), 0.41 °C (WC), and 0.18 °C (BC) (P < 0.05). Additionally, the WC application increased the fraction of aggregates of 1–2 mm in size (by 47.6%) and of 2–5 mm in size (by 65.8%), and the stability of soil aggregates (P < 0.05). All the amendments increased the soil pores (> 300 and 30–300 µm) of amended soils, but the saturated hydraulic conductivity of these soils was not significantly improved. CONCLUSION: The application of WC can improve the formation and stability of soil aggregates to reduce the risk of soil erosion. BC is suitable for use in drought-prone areas with low rainfall and strong evaporation because it can increase the retention capacity of soil water. GP should be applied with caution, considering that its decomposition after extraction leads to the severe loss of organic carbon to the atmosphere. Overall, the selection of organic amendments in agricultural management practices should take into account the local environmental conditions.