不同含盐土壤圆盘入渗特征试验

不同含盐土壤水分入渗特征是获得准确的土壤水力参数的基础。该文通过圆盘入渗试验,分析了4种土壤在5个（-1、-3、-6、-9和-12 cm）负水头下的入渗特征。结果表明,随着水头的减小,4种土壤的吸湿率线性减小,稳定入渗率和非饱和导水率呈不同程度减小。随土壤含盐量增加稳定入渗率和导水率呈增大规律。根据实测资料确定了不同负水头下非饱和导水率的Gardner指数模型参数,为盐渍化土壤水力参数的确定提供理论参考。     

Differences in ecological and allelopathic traits among Alternanthera philoxeroides populations

Based on a field investigation and laboratory trials, this study compared the invasive ecology of aquatic and terrestrial alligator weed (Alternanthera philoxeroides G.) ecotypes. The aquatic ecotype showed a stronger eco‐adaptation than the terrestrial ecotype. Alligator weed performed well in wetland and riparian habitats, where it was so competitive that only one‐to‐three other plant types grew successfully in its company. In contrast, it exhibited poor growth in upland fields and parks, where the terrestrial ecotype was dominated by 6–11 other alien plant species. The aquatic ecotype exhibited significantly greater growth inhibition of Microcystis aeruginosa. The ecotypes differed in their pattern of allelopathic inhibition of water blooms. The allelopathic effect of the aquatic ecotype persisted for a period exceeding 20 days, whereas the terrestrial ecotype's allelopathic effect subsided in <5 days. The aquatic ecotype had higher levels of antioxidant compounds, including soluble protein and flavones, and the activity of protective enzymes was also higher, which included superoxidase dismutase, peroxidase and catalase. Alligator weed's unique characteristics derive mainly from its strong allelopathic potential and tolerance of eutrophication in aquatic habitats.     

Hydrology in a patterned landscape is co-engineered by soil-disturbing animals and biological crusts

Water redistribution has a profound influence on dryland ecosystem function. This hydrological function is largely regulated by ecosystem engineers including biological soil crusts (biocrusts) which produce run-off, and burrowing animals, such as the greater bilby, whose pits capture water. We estimated the relative importance of these two ecosystem engineers in determining infiltration rates in a system where dune slopes shed water to adjacent interdune swales to maximize overall productivity. Also, we determined which biocrust property was most hydrologically important: total cover, composition, patch aggregation or spatial heterogeneity. While both biocrusts and burrowing animals equally affected the overall infiltration through macro- and micropores (under ponding), only biocrusts were important for the infiltration specifically via micropores (under tension). Of the studied biocrust properties, community composition was the strongest influence such that the greater the prevalence of early successional biocrust patches, the greater the infiltration rate. Greater total cover of biocrusts reduced infiltration, and the spatial properties were relatively unimportant. Although bilbies and biocrusts comparably influenced infiltration under ponding at the microscale, realistic cover of bilby pits at the landscape scale is unlikely to strongly impair the hydrological function of dunes. Reintroduction of the endangered bilby may enhance nutrient cycling and plant recruitment via its seed and resource capturing pits, without a concomitant disruption of hydrological function. In contrast, removal of biocrusts caused by, e.g., livestock trampling, is expected to strongly enhance infiltration in the run-off areas, strongly reducing ecosystem productivity at the landscape scale.     

Empirical reformulation of the universal soil loss equation for erosion risk assessment in a tropical watershed

Efficient intervention to control soil erosion in rural tropical landscapes requires accurate models for predicting the spatial location and intensity of degradation. The Universal Soil Loss Equation (USLE) has commonly been applied for spatial erosion risk assessment in the tropics, but has rarely been validated using ground observations of soil degradation. As with any empirical model, application in new regions requires calibration before results are used for decision support. We evaluated USLE effectiveness for predicting erosion in a small watershed in western Kenya based on 420 georeferenced ground observations of ordinal erosion class (three categories) systematically collected from throughout the basin. Relativized model factors were parameterized using standard remote assessment methods based on interpolated spatial data layers. Inference of degradation status at cultivated sites was estimated by calibration to near infrared diffuse reflectance spectra obtained from sampled soils; diagnostic models based on spectra produced validation accuracies of 78% for three categories. Association between USLE predicted risk and observed erosion, estimated using mixed effects logistic regression to control for within-site variability, correctly classified only 38% of sites into three degradation classes and model sensitivity for delineating regions of severe degradation was only 28%. Graphical modeling was used to identify those USLE risk factors that were conditionally associated with observed degradation, and an ordinal logistic regression model, employing only these factors was developed. This alternative model, which allowed statistical flexibility in estimating effect direction and strength, correctly predicted ordinal degradation class at 54% of field sites, with 55% sensitivity for the severe degradation class. This result suggests a critical need for efficient ground-based sampling schemes to be used in conjunction with flexible statistical models based on USLE factors for future investments in erosion risk assessment in the tropics.     

The effect of plastic mulch on the fate of urea-N in rain-fed maize production in a semiarid environment as assessed by 15N-labeling

A better understanding of the fate of fertilizer nitrogen (N) is critical to design appropriate N management strategies in plastic-mulched croplands. We evaluated the effects of plastic mulch on urea-N recovery by crops and loss from soil in furrow-ridge plots, with and without maize (Zea mays L.) cropping, in a semi-arid rain-fed site in China. We applied the same rate of urea-N (281 kg ha⁻¹) to all treatments during the preparation of the furrow-ridges in 2011 and 2012 but ¹⁵N-labeled the urea in 2011 only. We used transparent film to cover all soil surfaces in the mulched treatments and seeded maize in furrows in treatments with crop. In 2011, plastic mulch increased the total N uptake in the aboveground biomass of maize by 53%, whereas it decreased the in-season labeled-N uptake by 19%, compared to non-mulched treatment. At harvest in 2011, in mulched treatments the total labeled-N remaining in the 0−170 cm soil layer was 25% greater whereas unaccounted labeled-N was 69% less, than in non-mulched treatments, regardless of whether maize was cropped. In 2012 the effect of mulch on total maize N uptake was comparable to that in 2011, but the residual soil labeled-N uptake by maize was 63% higher in mulched compared to non-mulched treatment. At harvest in 2012, plastic mulch increased total labeled-N remaining in the 0−170 cm depth in cropped soils and unaccounted labeled-N in non-cropped soils, compared with no mulch. Our results indicate that plastic mulch profoundly changes the fate of urea-N in maize production in cold and dry croplands.     

第四纪黄土剖面多元古土壤形成发育信息的揭示

以时间尺度 2 0万年以来的洛川黄土剖面为研究对象。采用间隔 30～ 5 0cm的密集采样 ,通过土样的物理、化学、矿物组成和孢粉分析及土壤微形态镜鉴的综合研究 ,对第四纪生物气候环境演变提出了新的见解。对原以代表干冷环境沉积为主的黄土地层 (L) ,揭示了内伏半干旱环境的演化及相应的土壤发育过程 ;对原以代表暖湿环境的红褐色古土壤层 ,揭示了内伏干旱、半干旱环境的演化及干旱与湿润型孢粉共存的矛盾实质。研究证示 :深厚的黄土剖面是在第四纪生物—气候环境演变过程中 ,通过黄土沉积、成壤强弱交替演化 ,形成发育的由不同土壤类型组成的特殊的多元古土壤剖面体系。     

产流积水法测量坡地降雨入渗动态过程及其精度估计

坡地土壤的降雨入渗性能对于水文过程、土壤侵蚀、水资源相关方面的研究和实践非常重要。产流积水法采用由实验得到的数据，分析了不同坡位土壤入渗率及累积入渗量随降雨时间的变化过程。结果表明不同坡位入渗过程曲线反映了坡面径流到达前后，实际入渗率从降雨强度控制阶段跃升到入渗性能控制阶段，并最终趋于稳定入渗率的全过程。入渗区不同坡位的累积入渗量从坡顶至坡底逐渐减少，而且径流在坡面上推进速度越快不同坡位上的累积入渗量差值越小。通过理论分析，确定了观测径流推进距离误差所引起的测量结果的误差。用水量平衡原理对产流积水法实验结果进行精度估计，并提出了由实测入渗率求入渗水量的解析方法，并将此与实际降雨量进行比较，间接地估计了测量结果的精度。结果表明，产流积水法测量坡地降雨/径流入渗性能具有很高的精度。     

不同碎石含量及直径对土壤水分入渗过程的影响

由于成土原因或人类活动,一些土壤中含有不同含量及大小的碎石。碎石的存在改变了土壤的某些物理特性,入渗过程也因此受到影响。本研究采用定水头入渗试验装置,对7种不同碎石含量(0%,10%,20%,30%,40%,50%,60%)及4种不同碎石直径(0.2~0.5cm,0.5~1.0 cm,1.0~3.0 cm,3.0~4.0 cm)的土壤水分入渗过程进行室内研究,旨在分析碎石含量及直径对土壤入渗过程的影响及其原因,为土石混合介质的研究提供一些理论基础。