Search

White clay soils (Alfisols) are distributed widely in Heilongjiang Province, China, and are important agricultural soils in the province. However, only limited research has been done on the characteristics of these soils. Three representative profiles of these soils were selected to determine the uniformity of parent geological materials by evaluating the elemental ratios [zirconium/strontium (Zr/Sr) and titanium/zirconium (Ti/Zr)] in resistant minerals, mass ratios of different silt fractions, the mineralogy of clay and silt, and chondrite-normalized curves of rare earth elements (REE). The concentrations of Sr, Ti, and Zr were determined by x-ray fluorescence and REE were determined by instrumental neutron activation analysis. Minerals of clay and silt particles were identified by x-ray diffraction methods. The results showed low coefficients of variability associated with ratios of medium/coarse silt (8.3–13), Zr/Sr (5–10), and Ti/Zr (7.5–8.3) in the silt fractions between horizons. The types of minerals present in the clay and silt were the same among horizons. Chondrite-normalized REE curve patterns were very similar between horizons. Taken together, all these results indicate that the parent materials of each horizon of the white clay soils in this study were from the same source of geological material. The uniformity of parent geological materials between soil horizons is important for evaluating any change of soil properties during pedogenesis or caused by soil management. [ABSTRACT FROM AUTHOR]

• Total methane emissions from paddy fields in China are 8.20 Tg. • CH 4 emissions from early, late and single cropping rice are 1.12, 2.86 and 4.23 Tg. • Southern rice fields contribute 92% towards total CH 4 emissions. • CH 4 emissions hotspots were in Sichuan Basin, Heilongjiang, South and central China. • Water management, temperature and soil clay significantly affect CH 4 emissions. Methane (CH 4) emissions from rice fields across China were estimated using the DNDC (DeNitrification-DeComposition) model. The results showed that the CH 4 emissions from Chinese rice fields in 2012 were estimated to be 8.20 Tg CH 4 yr−1 (ranging from 4.80 to 11.40 Tg CH 4 yr−1); the values from early, late, and single cropping rice were 1.12, 2.86, and 4.23 Tg CH 4 yr−1. Rice fields in AEZ (agricultural ecosystem zoning) 7 (southeastern China) and AEZ 6 (central and southwestern China) were the two major sources, accounting for 92% of the total CH 4 emissions in China. The CH 4 emissions in AEZ 7 mainly originated from double cropping rice fields, while single cropping rice fields dominated the CH 4 emissions in AEZ 6. The CH 4 emission hotspots were in the Sichuan Basin of AEZ 6B (southwestern China), AEZ 6A (central China, except for Henan Province), AEZ 7 (except parts of Fujian and Zhejiang Provinces), and Heilongjiang Province. At the national scale, water management (positive correlation), air temperature (positive correlation), and the soil clay content (negative correlation) were the three dominant factors controlling the CH 4 fluxes in paddy fields. These results provide an understanding of the spatial distribution of CH 4 emissions from paddy fields and will help the government formulate policies to control CH 4 emissions at a regional scale. [ABSTRACT FROM AUTHOR]