Abstract
The development of reclaimed mine soils is normally spatially heterogeneous, making the fine management and utilization of reclaimed mined lands difficult. Soil nutrient grading can provide a scientific basis for the precise regulation of soil nutrients, but few related studies are available in reclaimed mined areas. This study aimed to quantify the spatiotemporal variations in soil nutrient grades under different land-use types in a reclaimed mined area on the Loess Plateau, China. The study area was graded by four soil nutrients (soil available potassium (SAK), soil available phosphorus (SAP), soil total nitrogen (STN), and soil organic matter (SOM)), and the variation features of soil nutrient grades in the initial stage of reclamation under four land-use types (i.e., cultivated land, grassland, forestland, and barren land) were systematically characterized by geostatistical analysis, pedodiversity analysis, and correspondence analysis. The results show that during the initial five years after reclamation, the soil nutrient grades of most reclaimed areas increased from Grade V and VI to Grade I–IV, while the improvements were significantly heterogeneous. Notably, the four land-use types had distinct variation characteristics. The barren land had the lowest SAP level, whereas it had the highest proportion, and medium–high grades of SAK, STN, and SOM (88.3, 100.0, and 100.0%, respectively). In terms of quantitative structure, it had the lowest richness index (S′, 2.5) and Shannon’s entropy index (H′, 0.7) and the highest evenness index (E′, 0.8). These results suggest that the barren land had relatively high and balanced nutrients, with the highest homogeneity among the four land-use types. The grassland had considerable improvement in all nutrients (especially SAP; 95.6% of the area had high SAP grades); however, its improvement was the most heterogeneous (S′ = 4.5, E′ = 0.7). As the second-most heterogeneous land-use type (S′ = 4.0, E′ = 0.8), the forestland had relatively low STN, SAP, and SAK levels due to high nutrient uptake and storage by tree species, but it had the highest proportion of area that reached high SOM grades (36.4%) and medium to high SOM grades (100.0%) due to its high community productivity. The cultivated land, which received fertilization for an additional three years, was the most imbalanced in terms of nutrients. It had the highest proportion of area that reached high SAP grades (98.0%); in contrast, its area proportions of low-grade SAK and SOM (69.0 and 32.9%, respectively) were the highest among the four land-use types. Based on the above comprehensive characterization of soil nutrient grade variation, guidance was given for fine management of reclaimed mined land and the optimization of reclamation measures.
Highlights
Coal resources are known as “black gold” and “industrial food” and are one of the main energy sources supporting China’s social and economic development
The high-grade SAP was mainly distributed in cultivated land and grassland, while the low-grade SAP was mainly distributed in forestland and barren land
Taking a representative opencast coal mine on the Loess Plateau as an example, this study applied the theories of geostatistics, pedodiversity, and correspondence analysis to grade the reclaimed mined land according to nutrient levels and to quantitatively characterize the spatiotemporal variation in nutrient grades under different land-use types
Summary
Coal resources are known as “black gold” and “industrial food” and are one of the main energy sources supporting China’s social and economic development. According to the National Bureau of Statistics, China’s raw coal production reached 3.75 billion tons in 2019, an annual increase of 4.2% [1]. While promoting the rapid development of China’s economy, coal mining has inevitably destroyed the ecological environment of the mining area and damaged the mine’s land resources. This is especially pronounced in opencast coal mining areas, where the original vegetation is devastated, the natural soil structure is disordered and the terrain is completely reformed [2,3,4]. As an effective measure for remediating the postmining environment, guiding ecosystem recovery into a desirable trajectory and recovering the utility value of postmining lands, has become an important means of coordinating coal resource extraction and land resource protection [5,6]
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