Grassland soil organic carbon and the effects of irrigated cropping in Alberta,Canada

High heterogeneity in the spatial distribution of soil organic carbon (SOC) in grasslands causes uncertainty in estimating its content and storage. In this study, we investigated the spatial distribution of SOC content and storage in the prairies of southern Alberta, Canada, and how it is affected by land use such as irrigated cropping and other environmental conditions such as cattle grazing, slope landscape position and dominant plant species. The mean SOC content was determined to be 11.5 g kg^–1 (range: 8.9 to 22.4 g kg^–1) in the 0–10 cm layer and 6.8 g kg^–1 (range: 4.0 to 13.3 g kg^–1) in the 10–30 cm layer; mean SOC storage was 1.59 kg C m^–2 (range: 1.23 to 2.78 kg C m^–2) in the 0–10 cm layer and 2.07 kg C m^–2 (range: 1.21 to 3.62 kg C m^–2) in the 10–30 cm layer. The SOC content was significantly affected by slope position in both the 0–10 and 10–30 cm layers, in the following order: bottom >middle > top position. Moreover, SOC storage was higher in sites dominated by shrubs than graminoid/forb communities. Thus, SOC content and storage had distinctly clustered spatial patterns throughout the study area and were significant differences between the 0–10 and 10–30 cm soil layers. Prior land-use change from arid grassland to irrigated cropland increased SOC content and storage in bulk soils.     

长期施肥下旱地红壤不同保护态有机碳库变化特征

为研究长期施肥对旱地红壤不同保护态有机碳组分（库）的影响,在不施肥（CK）、单施氮肥（N）、施常量氮磷钾肥（NPK）、施2倍量氮磷钾肥（HNPK）、氮磷钾肥配施有机肥（NPKM）、单施有机肥（M）6个处理下,分析物理-化学联合分组方法分离的土壤未保护、物理保护、物理-化学保护、物理-生物化学保护、化学保护、生物化学保护的有机碳组分的含量特征及其与总有机碳含量的关系,并探究土壤各保护态有机碳库储量与累积碳投入量间的关系。结果表明,CK与N处理间的土壤各保护态有机碳组分的含量均无显著差异（P>0.05）。与CK相比,施氮磷钾肥（NPK、HNPK）与有机肥（M、NPKM）处理的土壤总有机碳含量、未保护有机碳组分含量、物理保护有机碳组分含量分别提高13.3%～48.0%、39.2%～221.5%、41.9%～132.3%,土壤未保护有机碳、物理保护有机碳占土壤总有机碳的比例提高1.9～10.0、2.5～5.5个百分点,增幅均达显著水平（P<0.05）,该效应在施有机肥条件下表现更为明显。土壤各保护态有机碳组分含量与总有机碳含量均呈正相关关系,线性回归方程拟合结果显示,单位总有机碳含...     

土壤施硒对黑豆和黄豆硒质量分数及产量的影响

采用大田小区试验方法对黑豆和黄豆进行富硒栽培试验,研究硒对黑豆和黄豆产量、品质等的影响。结果表明,土壤施硒可以明显地提高黑豆和黄豆中总硒的质量分数,土壤施硒质量分数为0~250mg·kg-1时,黑豆和黄豆中总硒质量分数可达129~1 118和125~1 092μg·kg-1。土壤中施加硒质量分数为10~100mg·kg-1时,黑豆和黄豆的出芽率和产量与对照组相比均有所增加;在硒质量分数为60mg·kg-1时,黑豆和黄豆的出芽率和产量均达到最大值,分别为78.33%和54.79%,最高增产率为21.61%和28.19%;而后随着土壤中施加硒质量分数的增加,黑豆和黄豆的出芽率和产量与对照组相比均有所下降。硒质量分数较低时(10~40mg·kg-1),不利于黑豆和黄豆中蛋白质的积累,且在硒质量分数为40mg·kg-1时,黑豆和黄豆中蛋白质质量分数均达到最低值,较对照组分别减少20.67%和10.92%;随着硒质量分数的增加(60~250mg·kg-1),黑豆和黄豆中蛋白质质量分数开始逐渐增多,当硒质量分数为250mg·kg-1时,黑豆和黄豆中蛋白质质量分数积累最多,较对照分别提高1.38倍和1.22倍。由富硒黑豆和黄豆中可溶态硒的提取结果可知,在富硒黑豆和黄豆中,碱溶态酸溶态Tris-HCl态盐溶态水溶态。可见,黑豆和黄豆都具有一定的富硒能力,硒能在一定条件下使黑豆和黄豆增产,促进大豆蛋白质的积累,且在酸或碱性介质中更有利于硒的迁移转化,可溶性的有机硒质量分数较高。黑豆和黄豆富硒可大幅提高其营养价值,为进一步开发利用富硒大豆提供科学的理论依据。     

典型黑土的黑度与土壤有机质组分关系研究

土壤颜色作为土壤的一项重要物理指标，被广泛应用于土壤诊断、分类以及土壤性质判断。在矿物成分大致相同条件下，土壤有机质(SOM)是控制土壤变黑的重要因素。采用基于CIEL^*a^*b^*颜色分析系统的分光测色仪，并结合土壤物理分组方法，对30个典型黑土及其物理组分(轻组、粗颗粒、细颗粒和矿质结合态有机质)的黑度进行了分析，旨在明确黑土SOM含量与其黑度间的定量关系，揭示不同物理组分对土壤黑度的贡献。结果表明：黑土的黑度与SOM、以及各物理组分的黑度与相应组分的有机碳含量之间，均呈显著正相关关系。而且随着组分稳定程度的增加，这种相关性逐渐增强。从不同组分看，轻组和粗颗粒组分的黑度值大于细颗粒和矿质结合态组分，但相关分析表明，轻组和粗颗粒组分的黑度与原土黑度无显著相关关系，二者对土壤黑度的贡献率仅为2.6%。而矿质结合态组分作为土壤腐殖质的主要储存位置，其对土壤的黑度贡献率达81%以上，是黑土呈现黑色的决定性因素。     

Variations of soil organic carbon fractions in response to conservative vegetation successions on the Loess Plateau of China

Land use changes profoundly affect the equilibrium of soil organic carbon (SOC) sequestration and greenhouse gas emissions. With the current global climatic changes, it is vital to understand the influence of ecological restoration and conservation management on the dynamics of SOC under different land uses, especially in erosion-endangered Loess soils. Therefore, we investigated changes in SOC through a suit of labile fractions, namely: light fraction organic C (LFOC), heavy fraction organic C (HFOC), coarse particulate organic C (CPOC), fine particulate organic C (FPOC), and dissolved organic C (DOC), from two forests i.e., Robinia pseudoacacia (RP) and Platycladus orientalis (PO), with different ages, in comparison with farmland (FL). The SOC and STN contents significantly increased over 42 years in the RP forest where the contents of CPOC and FPOC were significantly higher than in the FL. Moreover, total SOC and its labile fractions, in the studied land use types, significantly correlated with soil CaCO₃, pH, and STN contents, indicating their key roles in SOC sequestration. The results reported here from different vegetation with different ages provide a better understanding of SOC and STN alterations at different stages of vegetation restoration. Our findings suggest that long-term natural vegetation restoration could be an effective approach for SOC sequestration and soil conservation on the Loess soil.