Effect of weathered coal on soil respiration of reconstructed soils on mining area's earth disposal sites in Shanxi-Shaanxi-Inner Monglia adjacent area

Abstract: Jin-Shan-Meng adjacent region is an important coal energy base in China, and also the most fragile ecological region. In recent years, the ecological system and landform have been destructed severely and widely because of opencast coal mining. So, how to improve the reconstructed soil rapidly and effectively on the earth disposal sites formed during coal mining becomes an important scientific problem for land reclamation and ecosystem restoration. Weathered coal, as a common organic material with an abundance of humus acid and oxygen-containing functional group, is probably an effective soil amendment material. However, adding weathered coal into soil in large scale might change the regional soil carbon cycling. To clarify the feasibility of weathered coal as an improvement material of soil quality and investigate the effect of weathered coal on soil respiration of the reconstructed soils on the earth disposal sites in this region, the soil respiration characteristics and the influence of soil temperature and soil moisture were studied. Two types of the reconstructed soils i.e. the local sandy loess (sandy loam) and the sandy loess mixed with soft rock were adopted, and the 2 components of latter soil were mixed at a ratio of 7:3 in weight; the thickness of soil layer covered was 50 cm. The 4 treatments with 3 replicates were set up as follows: sandy loess, sandy loess mixed with weathered coal, sandy loess mixed with soft rock, sandy loess mixed with soft rock and weathered coal. In July 2013, 12 trial plots of 4 m×5 m were constructed according to the treatments, weathered coal was added uniformly at the dose of 27 t/hm. During August and September in 2014, the soil respiration, temperature and moisture at 5 cm depth were monitored using Li-8100 system. The results showed that: 1) The response of soil respiration to soil temperature could be well simulated by vant' Huff model; the diurnal variation of sandy loess was a curve with single peak, however, the reconstruction soil with weathered coal addition showed a double-peak curve; weathered coal changed the diurnal variation pattern of soil respiration, and significantly increased soil respiration rate of the soft rock mixed sandy loess and the sandy loess by 35.2% (P<0.05) and 17.1%, respectively. 2) The sensitivity coefficients of soil respiration to the temperature of different reconstruction soils were relatively higher than the regular soils. Multiple linear regression analysis showed that the changes of soil respiration were consistent with soil temperature. And the soil respiration and soil temperature had extremely significant correlation, but soil moisture was not significantly correlated with soil respiration, which meant the soil temperature was the main controlling factor of the change of soil respiration. The results of the experiment can reveal the respiration characteristics of reconstruction soils in a certain degree, and provide a reference for the feasibility assessment of the weathered coal as amendment material to the reconstructed soil in the opencast coal mining region. In conclusion, soil temperature is the decisive factor of soil respiration in arid and semi-arid climatic regions. Objectively speaking, this experiment did not observe the soil respiration under the lower soil water content condition, since soil moisture in this experiment was relatively appropriate in arid regions. Under the condition of soil temperature and water condition in this experiment weathered coal can improve the soil respiration rate, in other words, it will promote the release of soil carbon. So in the practical work, the feasibility of the weathered coal as a new material for soil improvement needs to be further studied from the aspect of the carbon stability.