Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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Effects of biochar addition on evaporation in the five typical Loess Plateau soils
No full textSoil evaporation is the main route of soil moisture loss and often exceeds precipitation in the arid and semi-arid regions of the Loess Plateau. This study was conducted to determine whether biochar addition could reduce soil evaporation in drylands. We measured the evaporative loss in five typical topsoils (0-20 cm) from the Loess Plateau, Shaanxi, China, that differed in texture (Eum-Orthic Anthrosol, Isohumisol, Loess, Sandy loess, and Aeolian sand) with five different biochar addition amounts (0, 10, 50, 100, and 150 g-biochar/kg soil) and three biochar particle sizes (2-1 nun, 1-0.25 mm, and < 0.25 mm). The results showed that biochar addition generally increased the soil average water content (by 35.6% in biochar treatments and 33.5% in control treatments) and effectively reduced soil cumulative evaporation (by 322.64 gin biochar treatments and 326.68 gin control treatments). In addition, the inhibition of evaporation was enhanced with increases in biochar particle size and addition amount. Biochar addition had contrasting effects in the two evaporation stages: Biochar decreased evaporation through capillary flow during the first stage of evaporation but increased evaporation during the second, diffusion-limited vapour transport stage, particularly in the Aeolian sandy soil. When expressed on a mass basis, the effect of biochar addition amount on the cumulative evaporation (CE) was dependent on biochar particle size. In the larger sized (2-1 mm and 1-0.25 mm) biochar treatments, the final CE decreased as the addition amount increased, but for < 0.25 mm particles, increasing the biochar addition amount increased the final CE due to the creation of micropores. However, biochar addition decreased the ratio of evaporative loss in all soils proportional to the biochar addition amount. Soil texture and biochar particle size were the main factors affecting soil evaporation. Biochar application has the potential to improve soil water availability in semi-arid lands, but the results will depend on the biochar particle size and addition amount
Accumulation of N and P in the Legume Lespedeza davurica in Controlled Mixtures with the Grass Bothriochloa ischaemum under Varying Water and Fertilization Conditions
No full textWater and fertilizers affect the nitrogen (N) and phosphorus (P) acquisition and allocation among organs in dominant species in natural vegetation on the semiarid Loess Plateau. This study aimed to clarify the N and P accumulation and N: P ratio at organ and plant level of a local legume species mixed with a grass species under varying water and fertilizer supplies, and thus to fully understand the requirements and balance of nutrient elements in response to growth conditions change of native species. The N and P concentration in the organ (leaf, stem, and root) and plant level of Lespedeza davurica (C-3 legume), were examined when intercropped with Bothriochloa ischaemum (C-4 grass). The two species were grown outdoors in pots under 80, 60, and 40% of soil water field capacity (FC), NP, C N, C P, and C NP supply and the grass: legume mixture ratios of 2: 10, 4: 8, 6: 6, 8: 4, 10: 2, and 12: 0. The three set of treatments were under a randomized complete block design. Intercropping with B. ischaemum did not affect N concentrations in leaf, stem and root of L. davurica, but reduced P concentration in each organ under P fertilization. Only leaf N concentration in L. davurica showed decreasing trend as soil water content decreased under all fertilization and mixture proportion treatments. Stems had the lowest, while roots had the highest N and P concentration. As the mixture proportion of L. davurica decreased under P fertilization, P concentration in leaf and root also decreased. The N concentration in L. davurica at the whole plant level was 11.1-17.2%. P fertilization improved P concentration, while decreased N: P ratio in L. davurica. The N: P ratios were less than 14.0 under C P and C NP treatments. Our results implied that exogenous N and P fertilizer application may change the N: P stoichiometry and influence the balance between nutrients and organs of native dominant species in natural grassland, and P element should be paid more attention when considering rehabilitating degraded grassland via fertilization application in semiarid Loess Plateau region
Efficacy of Natural Polymer Derivatives on Soil Physical Properties and Erosion on an Experimental Loess Hillslope
No full textRaindrops disperse large soil aggregates into smaller particles, which can clog soil pores, cause soil crusting, reduce rainfall infiltration and increase soil loss. It was found that natural polymer derivatives were effective in improving soil physical properties and decreasing soil erosion on an experimental loess hillslope. This study investigated the effect of new natural polymer derivatives (Jag S and Jag C162) on soil properties, rainfall infiltration and sediment yield at four rates of sprayed polymers (0, 1, 3 and 5 g/m(2)), three rainfall intensities (1, 1.5 and 2 mm/min) and a slope gradient of 15 degrees with a silt loam soil through simulated rain. The results showed that both Jag S and Jag C162 significantly increased the shear strength and improved the aggregates composition of the soil surface. The water-stable soil aggregates >0.25 mm increased from 9% to 50% with increasing rates of Jag S and Jag C162. Jag S and Jag C162 also effectively increased rainfall infiltration and final infiltration rate, and reduced erosion compared to controls without natural polymer derivatives added. However, higher rates of Jag S produced lower infiltration rates. Although both Jag S and Jag C162 effectively influenced soil physical properties and erosion, the effect of Jag C162 was more significant than that of Jag S
淳化黄土-古土壤序列黏土矿物分布特征及古环境意义
No full text【Objective】The loess-paleosol sequence on the Loess Plateau of China has been considered as an important information carrier recording changes in the global environment and climate of the Quaternary peroid. As weathering products of land surface, clay minerals are widely found in Quaternary sediments, and their paleoenviromental significance has also attracted more and more attention. It has been documented that the formation and transformation of clay minerals is closely related to climatic conditions. However, so far, few studies have been reported on characteristics of the clay mineral in loess-paleosol profiles in the southern part of the Loess Plateau. Besides, previous researches about paleoclimate evolution in the south Loess Plateau focused mainly on Holocene, with little attention to climate changes in the Pleistocene. 【Method】 In this paper, a typical loess-paleosol profile of the Loess Plateau was selected in Chunhua County, Shaanxi Province, south of the Loess Plateau as research object. With the aid of the X-ray diffraction method, qualitative and semi-quantitative analyses of the soil samples from different layers of the Chunhua loess-paleosol profile were carried out for analyzing relative contents of clay minerals, illite/chlorite ratio (I/C value) and illite crystallinity (IC value), as well as regularities of their evolutions, and further for relationships of the characteristics of the clay minerals in the profile with changes in paleoclimate and eventually, for regularities of the evolution of the paleoclimate and paleo-environment in the Pleistocene in the south Loess Plateau. 【Result】Results show: (1) The three indices, i.e. relative content of clay minerals, ratio of illite to chlorite (I/C values) and illite crystallinity (IC value) of the Chunhua loess-paleosol profile are good indicators to be used in reversion of paleoclimate changes in the Pleistocene. (2) All the soil layers of the profile had the same clay minerals, but relative contents of the clay minerals varied significantly from layer to layer. During the period from the early Pleistocene to the mid-middle Pleistocene (WL-3～S5), the clay minerals were composed mainly of illite－montmorillonite－chlorite－kaolinite－vermiculite, and this period could be divided into two stages according to the changes in relative contents of the clay minerals. From the early Pleistocene to the early middle Pleistocene (WL-3～L11), the relative content of illite was comparatively low while the relative content of chlorite was quite high, which indicates that a cool temperate climate prevailed in this period. However, in the mid-middle Pleistocene ( S10～S5), the relative content of illite increased, while the relative content of montmorillonite and chlorite decreased, which indicates that the climate was relatively warmer and more humid in this period. In the late middle Pleistocene (L5～S1), the composition of clay minerals turned to be of illite － chlorite － vermiculite － kaolinite －montmorillonite, and the relative contents of illite and chlorite increased, implying a dry-cold climate dominated this period. Therefore, the changes in relative contents of the clay minerals in the Chunhua loess-paleosol profile indicate that from the early Pleistocene to the late middle Pleistocene, the climate generally became dry and cold, and experienced changes from cool temperate to warm wet and to cold dry. (3) The ratio of illite to chlorite (I/C value) and illite crystallinity (IC value) also exhibited phased variations from the bottom to the top of the Chunhua profile, that is increasing first and then decreasing. The distribution of I/C ratio and illite crystallinity indicates that the climate in the Pleistocene underwent an evolution process similar to that of the clay minerals in relative content. 【Conclusion】All the findings in this research are found to be conductive to the exploration of changes in the climate and environment of the south loess-paleosol during the Pleistocene, and may serve a scientific basis for comprehensive exploration of changes in climate and environment of various regions of the Loess Plateau during the Quaternary period of the Pleistocene. ;黄土-古土壤序列是记录第四纪气候环境变化的良好信息载体之一。以黄土高原南缘陕西省淳化黄土-古土壤序列为研究对象，通过 X 射线衍射法对黄土-古土壤剖面上黏土矿物进行定性与半定量分析，调查不同土层黏土矿物相对含量及伊利石/绿泥石比值（I/C 值）的变化规律，并结合伊利石结晶度的变化特征，探讨不同土层黏土矿物特征所对应的气候变化规律，揭示黄土高原南部地区在更新世时期的气候环境演变规律。结果表明：（1）淳化剖面黏土矿物的相对含量、I/C 值以及伊利石结晶度 IC 值在反演古气候方面具有较好的指示性。（2）淳化剖面不同土层的黏土矿物类型基本相同，但其相对含量存在差异。在 WL-3～S5 阶段，即早更新世至中更新世中期，黏土矿物的组合类型为伊利石－蒙脱石－绿泥石－高岭石－蛭石，其中早更新世至中更新世早期（WL-3～L11 阶段），伊利石相对含量相对偏低，气候以温凉为主，而中更新世中期（S10～S5 阶段），伊利石相对含量上升，但蒙脱石、绿泥石含量均降低，气候相对温湿；在中更新世晚期（L5～S1 阶段），黏土矿物的组合类型改变为伊利石－绿泥石－蛭石－高岭石－蒙脱石，以伊利石和绿泥石为主，气候较为干冷。黏土矿物类型及含量表明淳化地区从早更新世早期到中更新世晚期气候环境总体干冷化，并经历了温凉－温湿－干冷的变化过程。（3）I/C 值以及伊利石结晶度 IC值从剖面底部到顶部均经历了由小到大再到小的过程，它们与黏土矿物的含量所反映的气候变化规律一致。本研究有助于探索黄土高原南部地区在更新世时期的气候环境变化，为全面了解更新世黄土高原不同地区第四纪气候环境演变提供依据。 </p
毛乌素沙地生物结皮的空间分布及多种生态功能研究
No full text生物结皮在维管植物生长受限的干旱、半干旱生态系统中广泛分布，在防止水土流失、调节土壤水文、促进土壤养分循环等生态系统功能方面发挥着重要作用。掌握生物结皮的空间分布及其生态功能，对合理评估生物结皮的贡献，对生物结皮资源的科学管理与保护具有重要意义。为从区域尺度上了解生物结皮的空间分布状况及其多种生态功能，本研究基于40个样地的样方调查和1个典型样地的定位监测，结合室内分析测定，获取了各样地的立地环境指标、生物结皮生长指标，以及监测小区的土壤水分和风蚀数据，系统探讨了毛乌素沙地生物结皮的空间分布状况及其对土壤养分、土壤水分和土壤风蚀的影响，并借助结构方程模型分析了环境因子对生物结皮的影响。主要结论如下：
1）藻结皮和藓结皮在毛乌素沙地分布广泛，平均盖度分别为14.1%和11.3%，平均厚度分别为4.5 mm和7.5 mm；苔藓植物的平均株高度2.0 mm，平均生物量为2.2 g/cm2。藓结皮盖度自西北向东南呈递增趋势，藻结皮在北部地区盖度较高并呈现出自北向南减小的趋势。苔藓植物生物量自西向东呈逐渐增加的趋势。
2)地块尺度上：生物结皮多呈斑块状分布于水分条件较好的灌木林地、沙丘间低洼地，并呈现出不同的发育阶段；移动沙丘、沙化草场、农田以及城市内部等区域几乎不存在生物结皮。区域尺度上：藓结皮在东南部和东北部的沙地边缘地区为主导的生物结皮类型，而藻结皮在中部和西北部地区占主导；西南部地区生物结皮比较稀少。中西部地区藻结皮多为发育中期，北部、东部和南部沙地边缘的藻结皮均能达到发育末期；除西部少数地区，整个区域的藓结皮大多发育至中期和末期。
3）毛乌素沙地的藻结皮和藓结皮均能提高结皮层及其下伏5 cm土壤层的有机碳、全氮和全磷含量。相较于植被下的裸地，藻结皮存在能够提高沙蒿下0-30 cm土层以及柠条和沙柳下30-80 cm土层的水分含量；藓结皮存在能够提高3种灌木下方0-80 cm土层的水分含量。藻结皮和藓结皮覆盖后能够减少沙蒿、沙柳和柠条这3种灌木下方土壤的风蚀量。
4）结构方程模型的分析显示，由坡度、坡向、海拔表征的地形因子以及放牧干扰因子与藻结皮生长状况、土壤因子、植被因子之间的相关性微弱；干燥度与植被盖度呈显著负相关，表明干旱对植物生长有抑制作用；干燥度与藻结皮生长状况之间呈不显著的负相关，干旱抑制植被生长可能对藻结皮生长产生间接影响。干燥度与藓结皮的生长状况之间呈显著的正相关，干旱抑制植物生长可能对藓结皮生长产生促进作用；植被盖度对藓结皮下伏5 cm土壤有一定的积极影响，藓结皮下伏5 cm的土壤状况与藓结皮生长状况之间呈不显著的正相关。<br /
The mechanisms of soil organic carbon (SOC) loss and its modeling
No full text水力侵蚀造成的土壤有机碳（SOC）流失不仅会导致土壤退化、土地生产力下降，还会在一定程度上加剧全球变暖。因此，侵蚀导致的SOC流失成为全世界关注的重要环境问题。在以往的研究中，虽然SOC流失特征及规律已经得到了广泛研究，但是较少涉及其与径流水力特性的内在联系。水力学模拟一直是土壤侵蚀建模的经典方法。因此，充分了解不同侵蚀环境下SOC流失的径流水动力学机制，建立基于径流水力因子的SOC流失模型具有重要意义。本研究按照土壤黏粒含量依次递减的规律，选取了黄土高原四种典型的坡耕地土壤：塿土（杨凌）、黑垆土（长武）、黄绵土（安塞）和黄绵土（绥德），结合人工模拟降雨技术，研究了雨强、坡度和土壤质地交互作用下SOC的流失特征及规律、SOC流失的水动力学机制，并建立了基于径流水力因子的SOC流失模型。主要研究结论如下：
（1）系统研究了雨强、坡度和土壤质地交互作用下SOC流失特征及其规律，阐明了产沙量与SOC流失量的关系。研究结果表明，在试验雨强和坡度范围内，塿土、黑垆土、黄绵土（安塞）和黄绵土（绥德）的侵蚀泥沙有机碳富集比（ERoc）依次在1.15-2.36（平均值1.74）、1.18-1.69（平均值1.27）、1.06-1.34（平均值为1.12）和0.97-2.22（平均值为1.60）的范围内变化，而侵蚀泥沙中各粒级泥沙颗粒含量的变化趋势与ERoc相似，均随降雨历时的变化较小。塿土、黑垆土、黄绵土（安塞）和黄绵土（绥德）的土壤侵蚀速率依次为66.59、67.33、22.79和152.15 g m−2 min−1；SOC流失速率为0.28、0.20、0.06和0.14 g m−2 min−1。SOC流失速率与土壤侵蚀速率随土壤质地的变化趋势基本一致，因而产沙量在一定程度上决定了SOC流失量。进一步对产沙量与SOC流失量的关系研究发现，产沙量与SOC流失量呈显著正相关（P < 0.05）。然而，当土壤SOC含量较高时，由于SOC更易于在侵蚀泥沙中富集，侵蚀泥沙ERoc值较大，从而导致产沙量与SOC流失量的相关性减弱。此外，雨强和坡度对产沙量和SOC流失量的相关性也有重要影响。由于侵蚀泥沙ERoc值随雨强或坡度的降低而增大，从而使产沙量与SOC流失量的相关性减弱。研究还发现，随着土壤黏粒含量的增大，坡度和雨强对产沙量和SOC流失量的相关性的影响变小。不同土壤类型的黄土随坡度的变化规律存在差异，塿土和黄绵土的产沙量和SOC侵蚀量随坡度呈先增大后降低的趋势，而黑垆土的产沙量和SOC流失量在实验坡度范围内始终随着坡度的增大而增大。
（2）通过深入分析侵蚀过程中径流水动力学特征的变化，探明了径流流速、径流深、剪切力和径流功率与侵蚀泥沙SOC含量的内在关系，提取了可以较好表征侵蚀泥沙SOC富集比（ERoc）变化过程的水动力学因子。研究结果表明，土壤质地、雨强和坡度交互作用下径流流速始终与侵蚀泥沙SOC含量呈显著正相关（R2 = 0.731；P < 0.001），而径流深、剪切力和径流功率与侵蚀泥沙SOC含量无显著相关。通过对土壤质地对流速和侵蚀泥沙SOC含量的关系的影响进行研究发现，土壤质地在一定程度上决定了径流流速，且流速随着土壤黏粒含量的增大而增大；由于土壤黏粒含量与其SOC含量呈正相关，因此，流速与侵蚀泥沙SOC含量呈显著正相关（R2 = 0.893；P < 0.01）。进一步分析雨强对流速与侵蚀泥沙SOC含量的关系的影响发现，当雨强较低时，径流流速和径流功率均与泥沙中SOC含量较高的黏粉粒或轻质团聚体含量呈正相关关系，因而流速与泥沙ERoc值呈正相关。因此，当雨强较低时，流速与侵蚀泥沙SOC含量的决定系数更高（R2 = 0.958，P < 0.001）。在土壤质地、雨强和坡度交互作用下，流速可以较好地表征侵蚀泥沙SOC含量的变化。
（3）通过监测SOC迁移的径流水文水力过程，揭示了径流水动力学特征与侵蚀泥沙中SOC分布特征的关系。研究结果表明，当雨强小于45 mm h−1或坡度小于5°时，径流功率与径流深均较小，雨滴剥蚀团聚体破碎及其迁移过程对侵蚀泥沙ERoc值有重要影响，且泥沙各粒径团聚体SOC含量较原土壤明显增大。当雨强为45 mm h−1时，虽然泥沙各粒径团聚体SOC均发生明显富集，然而不同坡度条件下泥沙团聚体SOC含量无显著差异（P < 0.05）；然而，当坡度为5°时，随着雨强的增大，更多团聚体破碎形成粒径更小的颗粒，因此，微团聚体和黏粉粒的ERoc值随着雨强的增大而增大。当雨强大于45 mm h−1且坡度大于5°时，由于径流功率和流速足够大，较大的土壤侵蚀率削弱了团聚体破碎及其迁移过程对泥沙SOC分布特征的影响，因此，泥沙各粒径团聚体SOC含量与原土壤差异不显著（P < 0.05）。在降雨侵蚀过程中，由于产流率和径流深随着降雨历时的增大而增大，也减弱了雨滴对土壤团聚体的剥蚀作用，因此，泥沙各粒径团聚体SOC含量随降雨历时的增加呈降低的趋势。此外，流速、产流率、剪切力和径流功率与均与泥沙黏粉粒含量、黏粉粒SOC含量和微团聚体SOC含量呈负相关，而与泥沙砂粒含量呈正相关，且流速与泥沙中大团聚体含量随坡度和雨强的变化趋势最为一致。因此，众多水动力学参数中，片蚀阶段流速仍然与侵蚀泥沙SOC富集的关系最为密切。
（4）结合SOC流失的径流水动力学机制，建立了基于径流水动力学特征的SOC流失模型。研究发现，对于黄绵土，在不同雨强条件下，流速均与径流含沙量呈显著线性关系（R2 > 0.94，P < 0.05），而坡度与径流量呈显著二次函数关系（R2 > 0.94，P < 0.05）。对于黑垆土，含沙量和径流量均与坡度呈显著二次函数关系（R2 > 0.55，P < 0.05）。基于上述关系对黄绵土和黑垆土的产沙量进行了简单计算。在产沙量计算的基础上，采用传统SOC流失计算方法对SOC流失量进行预测，结果表明，该方法的预测精度主要取决于土壤侵蚀量的预测精度，且已有的泥沙SOC含量计算方法难以适用于黄土坡面。为了提高黄土坡面SOC流失量的预测精度，通过非线性回归分析发现，流速、坡度和雨强与侵蚀泥沙SOC含量之间为复合指数函数关系（R2 = 0.76，P < 0.005）。同时，结合已有的径流输沙模型，构建了基于径流水动力学特征的SOC流失模型。该模型以径流量、流速、坡度、泥沙分散前后的中值粒径差值（δD50）、原状土SOC含量和降雨时间作为输入参数，且可以较好预测SOC流失量。模型共包括四个方程，其中三个方程用于模型系数的计算。分析模型的决定系数（R2）和一致性指数（d）发现，土壤团聚体含量对模型精度有重要影响，对于δD50值较小的黄土，模型精度较好（R2 > 0.903，d > 0.974），对于δD50值较大的黄土，模型预测精度较低（R2 > 0.496，d > 0.861）。此外，模型也进一步证明了，δD50值越大，流速对土壤侵蚀量和SOC流失量的影响越大，而土壤SOC含量越高，坡度对土壤侵蚀量和SOC流失量的影响越大。该研究可为其他土壤类型和流域尺度下SOC流失预测提供新的思路
Beryllium-7 measurements of wind erosion on sloping fields in the wind-water erosion crisscross region on the Chinese Loess Plateau
No full textSoil erosion is complex in the wind-water erosion crisscross region of the Chinese Loess Plateau, as interleaving of wind and water erosion occurs on both temporal and spatial scales. It is difficult to distinguish wind erosion from the total erosion in previous studies due to the untraceable of aeolian particles and the limitation of feasible methods and techniques. This study used beryllium-7 measurements to study wind erosion in the wind-water erosion crisscross region on the Chinese Loess Plateau arms to delineate wind erosion distribution, to analyze its implication to erosive winds and surface microrelief, and to determine correlations between erosion rates and slope gradients. Results obtained using beryllium-7measurements based on observation plots were verified with saltating particle collection method, and were also verified on a field scale. Results indicated that the effective resultant erosion wind was from northward, which was proved by the eight-directional distributed saltating particles. The microrelief of the ground surface contributed to the formation of high or low erosion centers. Wind erosion rates increased with a linear (R-2 >= 0.95) or exponential (R-2 >= 0.83) fitting increase in the slope gradients as reported in previous studies. Compared to wind erosion on field scale, both the plots and fields exhibited similar distribution patterns in wind erosion isolines. We also determined that the wind erosion rate for two fields estimated, based on equations developed from plot scale was acceptable. This study validates the feasibility of beryllium-7 measurements for soil-wind erosion field experiments and the potential to expand this approach to real field conditions. (C) 2017 Elsevier B.V. All rights reserved