Determining the hot spots and hot moments of soil N2O emissions and mineral N leaching in a mixed landscape under subtropical monsoon climatic conditions

Abstract

Identification of hot spots and hot moments (HSHMs) in regard to soil nitrogen (N) losses has received public attention. Soil nitrous oxide (N2O) emissions and mineral N leaching under varied annual precipitation were simulated with the DayCent model in a mixed landscape (tea garden, bamboo forest and coniferous and broad-leaved mixed forests). Their HSHMs were further quantified using the 3rd quartile value of all data as the baseline. Results showed that the hot moments of soil N2O emissions were the dry year, summer, and months with high air temperature (July to September) and months after fertilization (April or May) at inter-annual, seasonal and monthly time scales, respectively. The hot moments of mineral N leaching at these time scales were the normal year or the wet year, spring or rainy seasons after drought, and rainy months after fertilization or drought, respectively. The main factors controlling the formation of hot moments on N losses were temperature, precipitation and fertilization. In addition, the hot spots of N2O emissions and mineral N leaching in the mixed landscape were both distributed in the tea garden (TG). When the entire study area was assumed to be under the same land-use type (i.e., TG), the hot spots of these two kinds of N losses were mainly distributed in the areas with rock fragment content < 0.16 cm3 cm−3, field capacity > 0.24 cm3 cm−3, bulk density > 1.29 g cm−3, soil carbon (C)/N ratio < 13.26, and slope < 12°. These results indicated that fertilizer management, climate factors, soil properties and topography need to be comprehensively considered to alleviate the formation of HSHMs of N losses in mixed landscape mountainous areas.