Reclaiming subsided land with Yellow River sediments: Evaluation of soil-sediment columns

A greenhouse experiment was conducted to investigate performance of columns containing varying layers of topsoil and subsoil (silt loam) and Yellow River sediment (sand) as proxies for designing reclamation strategies for subsided land in eastern China. Three control treatments (CK1, CK2, CK3) and 11 experimental treatments were established. CK1 consisted of 30 cm topsoil overlying subsoil and is a proxy for native (undisturbed) soil from the study sites. CK2 consisted of 30 cm of topsoil and 40 cm subsoil overlying sediment and is a proxy for conventional reclaimed soil. CK3 consisted solely of Yellow River sediment. All other treatments consisted of varying combinations of subsoil and sediment overlain by 30 cm of topsoil. These treatments were divided into four groups based on total subsoil thickness as follows: Group 1: 10 cm (T1); Group 2: 20 cm (T2, T3, T4); Group 3: 30 cm (T5, T6, T7) and Group 4: 40 cm (T8, T9, T10, T11). The treatments were used to evaluate morphological characteristics of maize, water and nutrient content of soil and sediment in columns during the experiment. The experimental results indicated a general trend of increase in magnitude of the selected maize characteristics (e.g., dry root biomass) with a corresponding increase in thickness of subsoil within sediment in the multilayered columns. Subsoil location and thickness influenced results as shown by comparison of Group 4 treatments with CK2, which each had the same total subsoil thickness. T8, T10 and T11 had greater dry root biomass at harvest than CK2 and T9. T9 had less % water content at 75 cm than the other treatments, which corresponds to 10 cm less subsoil in T9 in the 40-80 cm zone. Dry shoot biomass at tasseling was larger in T8 and T11 than in T9 and CK2; T10 had similar biomass to CK2 and larger than T9. T8, T10 and T11 had a subsoil layer at 80-90 cm, whereas T9 had a 70-90 cm sediment layer and a significantly smaller water content at 75 cm than T8, T9 and T11. Water content, available and total nitrogen, available and total phosphorous, available and total potassium, organic matter of topsoil and subsoil of all multilayered treatments were the same or larger than CK1 and CK2. This indicates that water and nutrient retention are not adversely impacted by inclusion of Yellow River sediment in the multilayered columns. The results show that strategically designed layered combinations of native subsoil and sediment can be used to construct soils that have favorable hydrological and chemical properties for maize growth. Sandwiching subsoil layers between sediment layers is a promising strategy for enhancing the hydrological capacity of the subsurface (30-120 cm) component of constructed soils. This study provides a guide for field experiments to evaluate optimal technological, agronomic and economic reclamation approaches in the study area and beyond where availability of native soil is insufficient to reclaim subsided land.