The decomposition, nutrient release characteristics and driving factors of straw under different C/N ratio were studied based on coal mining area, so as to provide as theoretical basis for the full utilization of straw resources and reclaimed soil fertility improvement.

Air-dried maize straw and wheat straw were cut into 2 mm pieces and were selected for decomposition experiment of a coal mining reclamation area in Shanxi Province. Two C/N ratio levels of 25 and 10 were designed in maize straw and wheat straw by supplementing urea, taking no nitrogen application that C/N ratio levels was 52 and 74 as the control. All the straws (8 g in organic carbon) were put into a nylon mesh bag (0.38 µm aperture), and horizontally buried into 15 cm deep of soil. On the 12, 23, 55, 218, 281 and 365 days after buried, samples were collected from the bags to analyze the dynamic of the dry matter residue and nutrient (carbon, nitrogen, phosphorus and potassium).

During the first 55 days, the adjusting the C/N on 25 with the application N was the best way to accelerate the decomposition of maize straw. Meanwhile, the adjusting the C/N on 10 was the best way to accelerate the decomposition of wheat straw. Application N could significantly promote the release of carbon and phosphorus from maize straw during the first 55 days. Application N could significantly accelerate the release of carbon, nitrogen and phosphorus from wheat straw, but had no significant effect on the release of potassium. The thermal equation of straw decomposition and nitrogen and potassium release was better than the temporal equation, and phosphorus release from straw was not suitable for the exponential decay equation. When the accumulated temperature was 4 600 ℃, the average release rates of carbon, nitrogen, phosphorus and potassium from straw were 49.2%, 39.5%, 40.8% and 90.3%, respectively; When the accumulated temperature reached 1 125 ℃, more than 85% the potassium of straw was released. The decomposition of straw was mainly influenced by the temperature, organic carbon, lignin and hemicellulose.

Application N could accelerate the decomposition of maize straw and the release of carbon and phosphorus in the early stage, which could significantly accelerate the wheat straw decomposition and the release of carbon, nitrogen and phosphorus too. Temperature could better reflect the process of straw decomposition and nitrogen, potassium release than time, the decomposition of straw was mainly regulated by the temperature, organic carbon, lignin and hemicellulose. Therefore, combined with the hydrothermal conditions in the coal mining area, the straw with an appropriate amount of urea should be returned to the field in the right time to improve the content of nitrogen, phosphorus and potassium of the reclaimed soil.