Effects of temperature on soil nitrogen mineralization in solar greenhouses with different cultivation years

【Objectives】 Vegetables cultivated in solar greenhouse are under a very intensive and unique production system in China. However, over-application of fertilizers is very common. As the development of this system in north China, it results in a series of problems, including the degradation of soil properties,groundwater pollution. Many studies found that the content of soil organic matter was increased as the age of solar greenhouse. Unlike open fields, soil temperature in solar greenhouse is higher, and could affect nitrogenmineralization from the greenhouse soils. However, there is few research to study this topic. 【Methods】 Soil samples (0-20 cm and 20-40 cm layers) were collected from greenhouses with different ages (0, 2, and 3 years) in Yangling, Shaanxi which locates at the south edge of Loess Plateau. The contents of soil organic matter and total nitrogen were analyzed. An incubation method (84 d) was used to study effects of different temperatures (20℃ and 30℃) on soil nitrogen mineralization in the solar greenhouses. The first order reaction model was used to fit curve of soil N mineralization, and nitrogen mineralization potential (N0) was used to evaluate the soil N mineralization. 【Results】1) The contents of soil organic matter, total N, and the accumulative mineralized N in different greenhouses are increased with the increase of greenhouse ages. 2) The soil mineralized N amount at 30 ℃ is higher than that at 20 ℃. The response of the mineralized N to temperature in soil with long cultivating history is higher than that in soil with short cultivating history. 3) As the increases of soil temperature and the cultivating history, the soil mineralized N amount is increased, and the soil N0 is also increased. There is a positive interaction between soil temperature and the cultivating history, however, the difference is not significant. 4) Compared to the soil before planting crops, the N0 values of soils with 2 and 3 years history are increased by 5.59 and 11.48 times, respectively. 5) The regression analysis indicates that the N0 values of soils at 20 ℃ and 30 ℃ are increased by 2.70 and 3.18 mg/kg when soil organic matter is increased by 1 g/kg, and when soil total N content is increased by 1 g/kg, the N0 values of soils at 20 ℃ and 30 ℃ are increased by 37.28 and 43.12 mg/kg, respectively. 【Conclusions】With the increase of cultivation year, the N mineralization from the greenhouses is increased significantly. When soil temperature increases from 20 ℃ to 30 ℃, the soil N mineralization is also increased. The accumulation of mineralized N of longer cultivated soil responses remarkably to the temperature changes. We conclude that when making sound N fertilizer recommendation for vegetable crops in solar greenhouses, the effects of temperature and cultivating history on the N mineralization from soil needs to be considered.