Optimum of interlayers in reconstructed soil with Yellow River sediment for restoring subsided coal mined land to farmland

Underground coal mining causes land subsidence, a large area of cultivated land is destroyed. The Yellow River interlayer filling reclamation technology is the powerful way to restore cultivated land. Understanding the mechanism of action of interlayers in reconstructed soil filled with Yellow River sediments is essential to achieving sustainable land management in the Yellow River regions. Column experiments and Field experiments were conducted to optimum of interlayers in reconstructed soil with Yellow River sediment for restoring subsided coal mined land. Our findings show that the inclusion of interlayers in the sediment reduced water leakage and moisture evaporation, and improved the water-holding capacity of the material in comparison to conventional reconstructed soil profile (Ck2). When the 30 cm thickness of interlayer, putting 2 interlayers in sediment (T6) was the optimal profile with the highest water-holding capacity. In comparison to CK2, the migration rate of wet front decreases by 32.16%, the cumulative evaporation decreases by 16.29%, the volumetric water content of filling layer (θ_fl) increases by 121.56%, and the water-holding coefficient (CWR) increases by 59.47%. It is also proved by field experiments. The wheat and maize yields of T6 improved 51.84% and 54.80%, respectively, as compared with CK2, that closer to undisturbed farmland (CK1). This study provides a valuable framework for subsided land reclamation regarding the method of placing interlayers into Yellow River sediment for enhancing water retention and productivity.

Heavy Mineral Variability in the Yellow River Sediments as Determined by the Multiple-Window Strategy

In this study, heavy mineral analysis was carried out in different size fractions of the Yellow River sediment to extract its end-members. It shows that heavy mineral contents, species, and compositions vary in different grain sizes. Distribution curve of heavy mineral concentration (HMC) and particle size frequency curve are in normal distribution. In most samples, the size fraction of 4.5–5.0 Φ contains the maximum HMC (18% on average). Heavy mineral assemblages of the Yellow River are featured by amphibole + epidote + limonite + garnet. Amphibole content is high in coarse fraction of >3.0 Φ and reaches its peak value in 3.5–4.5 Φ. Epidote is rich in a size fraction of >3.5 Φ, and increase as the particle size becomes fine. Micas content is high in coarse subsamples of <3.0 Φ, but almost absent in fine grains of >4.0 Φ. Metallic minerals (magnetite, ilmenite, hematite, and limonite) increase as the sediment particle size become fine, and reach the peak in silt (>4.0 Φ). Other minerals such as zircon, rutile, tourmaline, garnet, and apatite account for about 15%, and mainly concentrate in fine sediment. Further analysis reveals that similarity value between the most abundant grain size group and wide window grain size group is high (0.978 on average). The grain size of 4.0–5.0 Φ ± 0.5 Φ is suitable to carry out detrital mineral analysis in the Yellow River sediments. Our study helps to eliminate cognitive bias due to narrow grain size strategy, and to provide heavy mineral end-members of the Yellow River sediment for provenance discrimination in the marginal seas of East China.

Optimal Thickness of Soil Cover for Reclaiming Subsided Land with Yellow River Sediments

The cultivated land area per capita in China is relatively small compared to the world average. However, most of the coal output is coming from underground mining, resulting in land subsidence and the destruction of existing cultivated land. The Yellow River is known as a ground-suspended river due to its large sediment concentration. Using unpolluted Yellow River sediment to reclaim the coal mine subsidence not only solves the problem of sediment deposition, but also solves the problem of shortage of filling material. Some experimental studies revealed low soil productivity as a result of thin soil cover. To ensure crop growth and production in land reconstructed with Yellow River sediments, determining the optimal thickness of soil cover over the sediment is extremely important. There were four experimental treatments and one control treatment. Each treatment was repeated three times. The control treatment was an original soil profile with 30 cm topsoil plus 110 cm subsoil. The four experimental treatments with different thickness of soil covers had the same thickness of topsoil (30 cm) and Yellow River sediments (60 cm), and different thickness of subsoil, which were 10, 30, 40, and 50 cm, respectively. Thus, the total thicknesses of soil cover (topsoil plus subsoil) were 40 cm, 60 cm, 70 cm, and 80 cm, respectively. The topsoil, subsoil, and Yellow River sediments were collected from Liangshan County. The soil type is fluvo-aquic. Maize (Zea mays L.) is the main crop in Liangshan County. A greenhouse experiment was conducted to investigate the growth of maize. The results showed that (1) the peroxidase (POD) activity, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content of maize leaf decreased with an increasing thickness of soil, while soluble protein (SP) and leaf relative water content (RWC) increased. (2) The dry biomasses of the shoot and root system in T70 and T80 were not significantly different from those in the control (3) Increased soil thickness is conducive to the storage of more water and available nutrients. Considering the time and cost of reconstruction, 70 cm is the optimal thickness of soil cover on Yellow River sediment to ensure maize growth.