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To research soil organic carbon (SOC) in a typical small karst basin of western Guizhou in southwest China, data from the second national soil resource survey (1980) and data analysed in the laboratory in 2015 were used. This paper examines the changes in soil organic carbon density (SOCD) and soil organic carbon stock (SOCS) in the topsoil (0-20 cm) over the past 35 years based on soil types, and the primary influencing factors are also discussed. The SOCD and SOCS slightly increased over this period. The SOCD increased from 4.91 kg m−2 to 5.13 kg m−2, and the SOCS increased from 368.27 × 103 t to 385.09 × 103 t. The basin sequestered a low level of carbon during this time. Paddy fields were the key contributor to the increases, and the SOCD and SOCS of paddy fields increased by 1.61 kg m−2 and 32.39 × 103 t, respectively. Generally, the SOCD and SOCS in the soils from the southern part of Houzhai Basin increased considerably, and those from the northern part of the basin decreased significantly. The spatial variation of SOCD in the Houzhai Basin was mainly due to natural factors. However, the temporal change of SOC was primary caused by human activities. [ABSTRACT FROM AUTHOR]

[Objective] The objective of the paper is to discuss soil carbon, nitrogen, phosphorous content and their ecological stoichiometric characteristics, to explore ecological stoichiometric characteristics of soil nutrient elements and to provide the scientific basis for improvement of soil nutrient content in Guizhou province. [Method] The ecological stoichiometric characteristics of topsoil in Guizhou province are analyzed by using literature collection and ANO VA methods. [Result] The average value of SOC, TN and TP in soil of the research area was 27. 34, 2. 11 and 0. 7 4 g ·kg-1, respectively. C N, C: P and N: P was 14. 27, SO. 92 and 3. 75, respectively. The variance coefficient of SOC, TN, TP, C N, C P and N: P was 71. 22 %, 61. 61 %, 79. 73 %, 7S. S4 %, 90. 67 % and 78. 93 %,respectively. The spatial variability in TP and C P was the maximum. Soil SOC, TN, TP and their ecological stoichiometric characteristics were correlated significantly. [Conclusion] SOC, TP and C N in soil of Guizhou province is higher than SOC (17. 12 g ·kg-1), TP (0. S6 g ·kg-1) and C N (12. 30) of national land soil. The variance coefficient of soil SOC, IN, TP and their stoichiometric ratio ranges from 0. 1 to 1l. SOC is the main factor affecting TN, C N and C: P. [ABSTRACT FROM AUTHOR]

【Objective】The objective of the paper is to provide a reference for soil nutrient management and sustainable operation in Karst areas.【Method】The soil samples were collected from woodland and dry land in Baiduo Village(dolomite areas) and Shiqiao Village(limestone areas) in Shibing County,Guizhou Province,and then the soil nutrient was analyzed.【Result】The soil developed from dolomite was featured with higher organic matters,total N,available P,available K and hydrolysable N.The soil developed from limestone was featured with higher total P and total K.Total N was positively and very significantly related to hydrolysable N and organic carbon in soil developed from limestone and dolomite.Hydrolysable N was positively and significantly related to organic carbon in limestone areas.Hydrolysable N was positively and very significantly related to organic carbon in dolomite areas.Land use patterns had obvious effects on nutrient content in soil developed from limestone and dolomite.Soil total K,total N,hydrolysable N and organic carbon content in limestone woodland was higher than dry land,and available K,total P,available P and pH was lower than dry land.Soil total P and available P in dolomite woodland are lower than dry land,and other indexes are higher than dry land.The organic matter,total N,total P and total K content in dolomite-developed soil was Grade II,Grade I,Grade VI and Grade III respectively.The organic matter,total N,total P and total K content in limestone-developed soil was Grade II,Grade I,Grade V and Grade I separately.【Conclusion】Soil nutrient was not only affected by soil forming rock,but also affected by land use pattern. [ABSTRACT FROM AUTHOR]

The Carbon (C), nitrogen (N) and phosphorus (P) fractions, mineral element concentrations, microbial density, and biomass in 0–10 and 10–20 cm soil fractions under Zanthoxylum planispinum 'dintanensis' plantations, were measured at altitudes of 531, 640, 780, 871, and 1097 m in the mountainous karst areas of Guizhou Province, Southwest China, and the correlations between altitude and the soil variables were analyzed. The results showed that: (1) with the increase in altitude, there was no significant linear change in C fractions, total N, effective N, microorganism density, or mineral element concentration in each soil layer; however, ammonium-N and nitrate-N concentrations gradually decreased, and the P fraction was higher at the highest altitude; (2) soil C, N, and P fractions, concentrations of microorganisms and mineral elements at the same altitude showed a surface aggregation effect; (3) principal component analysis identified the main indicators affecting C, N and P fractions as total calcium, effective calcium, effective iron, total zinc, and bacteria; (4) correlation analysis showed that both total N and C fractions were positively correlated with effective N and P fractions and that mineral element concentrations were more closely correlated with C, N, and (especially) P fractions than with microorganism abundance. Overall, the effect of altitude on C, N, and P fractions showed that the correlation with soluble organic carbon was stronger than particulate organic carbon and easily oxidized carbon, inorganic N was closer correlated than organic N, and organic P was closer correlated than inorganic P. In conclusion, it shows that research focusing on soil N conservation, nutrient stoichiometry balance, and application of mineral-rich element fertilizers is important for Zanthoxylum planispinum 'dintanensis' plantation maintenance. [ABSTRACT FROM AUTHOR]

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The policy‐driven "Grain for Green Programme" (GGP) has resulted in large‐scale land conversion from agricultural land to natural land in the karst area. One research surrounding the GGP is focused on evaluating its ecological implications for total mercury (THg) enrichment in Yinjiang County, Guizhou Province, Southwest China. Results show that 1) THg content in agricultural land (201.85 ± 57.23 µg kg−1) is lower compared to the forest (1048.62 ± 306.19 µg kg−1) and shrub (2582.60 ± 614.76 µg kg−1). 2) The THg content shows a good correlation with Fe (agricultural land: R = 0.75, p < 0.01; shrub: R = 0.88, p < 0.01), pH (shrub: R = 0.87, p < 0.01), and sand proportion (forest: R = −0.65, p < 0.01), rather than soil organic carbon (SOC). In the shrub, the increased pH and iron (Fe) content correspond to THg content between 1804 and 3743 µg kg−1; below the depth of 80 cm of the forest soil, the increased sand proportion correlates to THg content between 1223 and 748 µg kg−1. 3) The risk index of the THg exceeds 320 in the soil and imposes a very high ecological risk to this area. [ABSTRACT FROM AUTHOR]