Northwestern Loess Plateau Research Articles

中国富士苹果种植气候适宜区的年代际变化

PDF HTML阅读 XML下载 导出引用 引用提醒 中国富士苹果种植气候适宜区的年代际变化 DOI: 10.5846/stxb201511072257 作者: 作者单位: 陕西省经济作物气象服务台,中国气象科学研究院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划973项目（2010CB951300）；中国气象局气象关键技术集成与应用项目（CMAGJ2015M60）；中国气象局气候变化专项（CCSF201621） Dynamics of decadal changes in the distribution of cultivation regions with climate suitable for the Fuji apple in China Author: Affiliation: Shaanxi Meteorological Service Station for Economic Crops,Shaanxi Meteorological Service Station for Economic Crops Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:苹果是中国种植面积最大的水果，分析气候变化背景下其种植气候适宜区的年代际变化，可为合理利用气候资源、科学应对气候变化提供参考。基于中国主栽的富士苹果地理分布信息和1961-2010年中国区域2084个气象台站资料，利用最大熵模型（MaxEnt）和ArcGIS软件，通过构建富士苹果种植分布与气候因子的关系模型，分析1961-2010年中国富士苹果种植分布的年代际变化特征及其对气候变化响应的敏感区。结果表明，气候变化导致中国富士苹果种植分布的气候界限和气候适宜区明显北移，其中气候适宜区范围伴有西扩趋势。富士苹果种植的各气候适宜区分布年代际变化特征明显，适宜气候种植面积显著增加，特别是1990s变化最为突出，2010s气候种植适宜面积较1960s增加36%。但高气候适宜区面积则呈年代际波动，2010s虽略高于1960s，但较1970s-1980s减少25%。富士苹果种植适宜区对气候变化响应最为敏感的地区主要分布在辽宁南部、鲁南、苏北、豫东南、黄土高原西北部和川陕接壤区。除热量条件外，年日照时数对富士苹果种植的气候适宜区面积影响显著，气候资源变化有助于富士苹果种植的气候适宜范围增加，但不利于高气候适宜区的稳定。 Abstract:Apple has larger planting area than any other fruit in China. Analyzing the decadal changes in the distribution of cultivation areas with climate suitable for apple under the background of climate change can provide a reference for the rational use of climate resources and adaptation to climate change. In this paper, we established a model by examining the relationship between Fuji apple cultivation distribution and climate, based on meteorological data from 1961 to 2010 at 2084 meteorological stations and the geographic planting distribution of Fuji apple in China together with the maximum entropy (MaxEnt) model and the ArcGIS spatial analysis technique. The decadal change characteristics of the distribution of Fuji apple cultivation areas in China from 1961 to 2010 and areas sensitive to climate change were explored using the model. The results showed that climate change has led to the northward movement of planting boundaries and areas with climate suitable for Fuji apple, with westward expansion of the areas with suitable climate. There was an obvious decadal change in areas with climate suitable for the cultivation of Fuji apple and this area increased significantly, especially in the 1990s. The cultivation area with suitable climate was 36% higher in the 2010s than in the 1960s; however, the optimum cultivation area fluctuated with decadal change. The optimum cultivation area in the 2010s was slightly higher than that in the 1960s, but was 25% lower than those in the 1970s-1980s. The most climate change-sensitive cultivation area of Fuji apple was principally found in southern Liaoning, southern Shandong, and northern Jiangsu, and on the southeastern Henan northwestern Loess Plateau and the contiguous area of the Sichuan-Shaanxi province. Annual sunshine hours and thermal conditions had significant effects on the areas with climate suitable for the cultivation of Fuji apple. Overall, climate change can act to increase the area suitable for cultivation of Fuji apple, but can adversely affect the stability of the optimum cultivation area. 参考文献 相似文献 引证文献

Spatiotemporal vegetation cover variations associated with climate change and ecological restoration in the Loess Plateau

Vegetation is an important component of terrestrial ecosystems, and it plays an important role in preventing desertification and conserving soil and water in arid and semi-arid regions. This study examined the spatial distribution and temporal variations of vegetation cover in the Loess Plateau over the last three decades using a time series of the normalized difference vegetation index (NDVI) derived from the long-term data record (LTDR) and the moderate resolution imaging spectroradiometer (MODIS) between 1981 and 2010, along with daily climate datasets. Furthermore, we assessed the relationships between the vegetation, climate variables (i.e., temperature and precipitation), and human activities, particularly the “Grain to Green” restoration program. The greenness of the vegetation cover in the Loess Plateau exhibited a significant increase from the northwest to the southeast. Generally, the NDVI exhibited an increase of 0.0015 year−1 (P<0.01) from 1981 to 2010 over the entire plateau, and the rate was particularly high over the last decade. The NDVI increases with a rate of more than 0.01 year−1 during 1991–2000 were distributed throughout the Ziwuling and Huanglongshan Forests in Yan’an, Shaanxi Province, and in the Lvliang and Taihang Mountains, Shanxi Province. However, the distinct feature of the NDVI, namely, its increase of more than 0.01 year−1 in 2001–2010, was associated with key areas of ecological restoration in Yulin and Yan’an in Shaanxi Province. The vegetation cover was largely improved within the last decade due to the “Grain to Green” program. However, revegetation still has great potential in the Huangfuchuan, Kuyehe, Wudinghe, and Yanhe watersheds in the future. In response to global warming, the phenology timing in the Loess Plateau was 3.9 days (1991–2000) and 6.6 days (2001–2010) earlier in spring compared with 1981–1990, and the end of the fall growing season was delayed 3.6 days and 9.6 days, respectively, over the past three decades. The significant and positive partial correlations (R>0.5, P<0.05) between the temperature and the NDVI occurred in the central and southeastern parts of the plateau; this finding indicates that higher temperatures promote the growth of vegetation in less water-stressed areas. However, a negative impact of vegetation degradation due to climate warming was found in the northwestern Loess Plateau. The permafrost slowly degraded in the northwestern Loess Plateau, causing a decrease in the water content of the topsoil, eventually leading to the adverse effects on vegetation.

Soil aggregation and intra-aggregate carbon fractions in relation to vegetation succession on the Loess Plateau, China

Revegetation has been reported to be one of the most effective measures for reducing soil erosion on the Loess Plateau in China. The Yunwu observatory, located in the northwestern Loess Plateau of China, was selected to study the effect of vegetation succession on total carbon (C), aggregate C, and intra-aggregate particulate organic matter-carbon (iPOM-C) concentrations. The vegetation types studied, listed from the shortest to the longest enclosure duration order, were abandoned grazed grassland (Ab.G3), Hierochloe odorata Beauv. (Hi.O7), Thymus mongolicus Ronnm (Th.M15), Artemisia sacrorum Ledeb (At.S25), Stipa bungeana Trin Ledeb (St.B36), and Stipa grandis P. Smirn (St.G56) communities. Five sizes of aggregates were separated using the modified Yoder method (<0.25mm, 0.25–1mm, 1–2mm, 2–5mm and 5–8mm). Fine and coarse iPOM-C concentrations were isolated from the soil aggregates. The results showed that revegetation led to an increase in the percentage of aggregates in small macroaggregates (0.25–2mm) and thereby improved the uniformity of the soil aggregate size distribution. The concentration of bulk soil carbon ranged from 10.1gkg−1 to 29.7gkg−1 during vegetation succession. During the vegetation succession, with the exception of At.S25, the bulk soil carbon and aggregate carbon concentrations increased with recovery time. The fine iPOM-C concentrations were between 0.7 and 14.0gkg−1, which was significantly greater than the coarse iPOM-C concentrations. The coarse and fine iPOM-C concentrations exhibited different trends with vegetation restoration. In conclusion, vegetation restoration caused an increase in small macroaggregates, enhancing the uniformity of the soil aggregate size distribution and inducing greater soil organic carbon sequestration.

Soil aggregate and crop yield changes with different rates of straw incorporation in semiarid areas of northwest China

The current cropping system of conventional tillage and stubble removal in the northwestern Loess Plateau of China is known to decrease the water use efficiency and crop yield because of reduced aggregation and aggregate stability, as well as degrading other soil properties. To determine the effects of straw incorporation on the soil aggregates and crop yield, we conducted experiments in semiarid areas of southern Ningxia for 4years (2007–2010). Four treatments were tested: (i) no straw incorporation (CK); (ii) incorporation of maize straw at a low rate of 4500kg/ha (L); (iii) incorporation of maize straw at a medium rate of 9000kg/ha (M); and (iv) incorporation of maize straw at a high rate of 13500kg/ha (H). In the final year of treatment (2010), the mean soil bulk density of the tilth soil (0–60cm) was decreased significantly with H, M and L, i.e., by 4.13%, 3.21% and 1.80% compared with CK, respectively, and the treatments greatly improved the total soil porosity. The straw incorporation treatments increased the soil aggregate size distribution and soil aggregate stability in the 0–40cm soil layers, according to the following order: H/M>L>CK. Straw incorporation significantly improved the soil moisture content compared with CK. Higher yields coupled with greater water use efficiency were achieved with H, M and L compared with CK, where these treatments increased the crop yields by 22.49%, 22.82%, and 10.62%, respectively, and the water use efficiency by 32.11%, 29.29%, and 14.05%.

English

This work was carried out in the Northwestern Loess Plateau (NLP), one of two main large-scale apple production areas in China. It is to investigate the role of nematodes in apple production areas, which cause apple replant disease (ARD). Soil samples from total eight sites in NLP were collected twice, in summer and autumn, respectively. The nematodes were extracted by washing-sifting-sucrose centrifugation and total nematodes in each sample were counted with the aid of an anatomical lens (40&times;). Furthermore, a sub-sample of one quarter of each nematode suspension was observed with a Motic microscope (400 and 1000&times;) and each nematode was identified to genus level using diagnostic keys. The results indicated that the characteristics of the nematode community did not vary significantly in four different types of soils. Especially, the diversity indices of nematode community did not show obvious differences. In addition, the analysis of nematodes with different feeding habits revealed that the overall number of Pratylenchus penetrans nematodes in the replanted orchard in NLP were far below the density threshold that could jeopardize apple trees. Thus, it appeared that the nematodes were not the leading causal agent for ARD in NLP. &nbsp; Key words: Apple replants disease, nematode diversity, nematode feeding habits, nematode community structure.

西北黄土高原半干旱区全膜覆土穴播对土壤水热环境和小麦产量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 西北黄土高原半干旱区全膜覆土穴播对土壤水热环境和小麦产量的影响 DOI: 10.5846/stxb201311272827 作者: 作者单位: 甘肃省农业科学院旱地农业研究所;西北作物抗旱栽培与耕作重点开放实验室;兰州 730070,甘肃省农业科学院旱地农业研究所;西北作物抗旱栽培与耕作重点开放实验室;兰州 730070,甘肃省农业科学院旱地农业研究所;西北作物抗旱栽培与耕作重点开放实验室;兰州 730070,甘肃省农业科学院旱地农业研究所;西北作物抗旱栽培与耕作重点开放实验室;兰州 730070,甘肃省农业科学院旱地农业研究所;西北作物抗旱栽培与耕作重点开放实验室;兰州 730070,甘肃省农业科学院旱地农业研究所;西北作物抗旱栽培与耕作重点开放实验室;兰州 730070 作者简介: 通讯作者: 中图分类号: 基金项目: 甘肃省杰出青年基金项目（1210RJDA011）；农业部公益性行业（农业）科研专项（201203031）；国家自然科学基金项目（31060071） Effects of whole field soil-plastic mulching on soil thermal-moisture status and wheat yield in semiarid region on Northwest Loess Plateau Author: Affiliation: Institute of Dryland Agriculture,Gansu Academy of Agricultural Sciences,Key laboratory of northwest Drought-resistant Crop Farming,Key Laboratory of Efficient Utilization of Water in Dry Farming,Institute of Dryland Agriculture,Gansu Academy of Agricultural Sciences,Key laboratory of northwest Drought-resistant Crop Farming,Key Laboratory of Efficient Utilization of Water in Dry Farming,Institute of Dryland Agriculture,Gansu Academy of Agricultural Sciences,Key laboratory of northwest Drought-resistant Crop Farming,Key Laboratory of Efficient Utilization of Water in Dry Farming,Institute of Dryland Agriculture,Gansu Academy of Agricultural Sciences,Key laboratory of northwest Drought-resistant Crop Farming,Key Laboratory of Efficient Utilization of Water in Dry Farming,Institute of Dryland Agriculture,Gansu Academy of Agricultural Sciences,Key laboratory of northwest Drought-resistant Crop Farming,Key Laboratory of Efficient Utilization of Water in Dry Farming,Institute of Dryland Agriculture,Gansu Academy of Agricultural Sciences,Key laboratory of northwest Drought-resistant Crop Farming,Key Laboratory of Efficient Utilization of Water in Dry Farming Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:全膜覆土穴播是西北黄土高原旱作区大面积应用于密植作物栽培的关键增产技术，可显著提高降水利用率和作物生产力，但目前对其增产机制和环境效应缺乏系统研究分析。在2011-2013年以春小麦陇春27号为试验材料，设全膜覆土穴播（FMS）、地膜覆盖穴播（FM）和露地穴播（CK）3个处理，研究半干旱旱作区全膜覆土穴播的土壤水热效应及其对小麦产量的影响。结果表明，小麦苗期FMS在 0-25 cm土层的平均地温比CK提高1.4-3.5℃，但孕穗到灌浆期正午地表地温比FM和CK分别降低5.3-6.4℃和3.1-4.3℃。FMS和FM使小麦拔节前0-200 cm土层土壤贮水量分别增加33.1和29.3 mm，且可促进小麦对深层水分（100-200 cm）的利用，FMS成熟期100-200 cm土层土壤贮水量比播前下降44.4-69.6 mm，较CK高8.4-145.5%，但FMS在休闲期补充土壤水分77-127 mm，分别较FM和CK增加4.5%-40.9%和12.8%-109.5%；FMS的休闲效率为30.5%-52.6%，比CK高12.8%-109.5%，比FM高4.5%-40.9%。基于对土壤水热环境和作物耗水的影响，FMS的产量达1750-3180 kg/hm2，水分利用效率为5.5-11.5 kg hm-2 mm-1，分别比CK增加40%-220%和27%-239%，而且干旱年份的增加幅度更高。因此，FMS改善了小麦生长前期的土壤水热条件，调节作物不同生育期的耗水强度，显著提高作物水分利用效率和产量，并提高降水休闲效率，使小麦生育期耗散的土壤水分在休闲期得到有效补充。 Abstract:The main factors that limit wheat productivity on the northwestern Loess Plateau in China are drought, low temperature in spring, and the seasonal rainfall dynamics, which do not meet the water requirements of wheat. Efficient conservation of rainwater in the soil, and its utilization in the wheat-growing period, are the most important means of increasing wheat yield in this region. Whole-field plastic and soil mulching (i.e., the whole soil surface in a field is first mulched with plastic, on top of which a soil layer about 1 cm thick is spread), which is commonly used for high-planting-density crops on the Loess Plateau, could significantly improve rainfall use efficiency and crop productivity. However, no systematic analysis of the productivity increment and environmental effects of this technique has been undertaken previously. Spring wheat (Triticum aestivum cv. Lunchun 27) was selected as the test material for a field experiment conducted from 2011 to 2013 to study the effects of whole-field plastic and soil mulching on soil temperature, soil moisture, water use efficiency and wheat yield. The three treatments applied were 1) whole-field plastic and soil mulching and bunch seeding (FMS), 2) whole-field plastic mulching and bunch seeding (FM), and 3) soil uncovered and bunch seeding (CK). The seasonal soil water content, soil temperature, and wheat yield were recorded and the rainwater fallow efficiency, evapotranspiration, and water use efficiency were calculated. The FMS treatment increased average soil temperature in the 0-25 cm soil profile by 1.4-3.5℃ compared with CK at the seedling stage, and reduced the surface ground temperature by 5.3-6.4℃ and 3.1-4.3℃ compared with FM and CK, respectively, at 14:00 from the booting stage to the filling stage. Both FMS and FM treatments improved soil water storage in the 0-200 cm soil profile by 33.1 mm and 29.3 mm, respectively, compared with CK before the jointing stage. Water storage was lower at deeper soil depths (100-200 cm) in FMS and FM compared with CK. At the maturing stage, the soil water storage in the 100-200 cm soil profile of the FMS treatment decreased by 44.4-69.6 mm compared with before the seeding stage, which was 8.4-145.5% higher than that of CK. However, the soil water of the FMS treatment was recharged by 77-127 mm in the fallow period, which was 4.5-40.9% and 12.8-109.5% higher than that of FM and CK, respectively. The rainwater fallow efficiency of FMS was 30.5-52.6%, which exceeded that of CK and FM by 12.8-109.5% and 4.5-40.9%, respectively. Based on the regulatory effect of soil thermal-moisture status and crop water use, the wheat yield and water use efficiency of FMS were 1750-3180 kg/hm2 and 5.5-11.5 kg hm-2 mm-1, respectively, which were 40-220% and 27-239% higher than those of CK. The increased extent of yield and water use efficiency were higher in a dry year than that in a wet year. Consequently, FMS ameliorated soil thermal-moisture status, optimized wheat water use, and increased wheat water use efficiency and yield. Rainwater fallow efficiency was significantly higher in FMS, so the soil water consumed in the wheat-growing period was recharged completely in the fallow period, which is important for maintenance of the inter-annual soil water balance. 参考文献 相似文献 引证文献

Timing and lock‐in effect of the Laschamp geomagnetic excursion in Chinese Loess

The Laschamp geomagnetic excursion (LGE, at ∼41 ka) is a critical age control for hemispherical comparison of paleoclimate records from various kinds of geological archives (e.g., ice core, marine, and lake sediments). The timing of the LGE in Chinese Loess, however, remains poorly constrained due to the lack of a reliable chronology and the complex acquisition processes of natural remanent magnetization. Here, we systematically compare the paleomagnetic results of three optically stimulated luminescence dated loess sequences on the Chinese Loess Plateau. Our results indicate that the timing of the LGE in the northwestern Loess Plateau is slightly older than the absolute radiometric age determination and the timing inferred from Greenland ice core (10Be flux) and marine (i.e., relative paleointensity and authogenic 10Be/9Be stack) records, but younger than the counterparts in the central Loess Plateau. We attribute the different timing of the LGE in the three loess sections to a progressive southeastward increase in the lock‐in depth caused by the combined effects of postdepositional processes (e.g., surface mixing, chemical weathering, and lock‐in delay) on the remanence acquisition process. We conclude that caution is needed to use the LGE in Chinese Loess as a reliable tie‐event for high‐resolution chronological correlation to marine and ice core records, only if the potential lock‐in effect can be precisely determined.

Effects of thermally transferred signals in the post-IR IRSL SAR protocol

Abstract The recently developed post-IR IRSL SAR protocol is promising to isolate more stable IRSL signals of feldspars. However, the high temperature thermal treatments used will inevitably induce thermally transferred post-IR IRSL295 (TT-post-IR IRSL295) signal, which would contribute to the measured post-IR IRSL295 signal of the test dose and may lead to inaccurate sensitivity correction. In this study, the effects of TT-post-IR IRSL295 signal in the post-IR IRSL295 SAR protocol are investigated using medium polyminerals from a loess section at Caoxian, northwestern Loess Plateau in China. The sensitivity changes of the IRSL50 and the post-IR IRSL295 signals are different from natural cycle to regenerative cycles, which can be attributed to the interference of the TT-post-IR IRSL295 signal. Such difference is dependent on the test dose and the post-IR IR stimulation time. The TT-post-IR IRSL295 signal is also shown to affect the post-IR IRSL295 Do and De values and to cause overestimation of the fading rates. Our study therefore highlights the need of serious consideration on the effects of TT-post-IR IRSL signal when the post-IR IRSL SAR protocol is employed for dating.

The effects of stubble retention and tillage practices on surface soil structure and hydraulic conductivity of a loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and stubble management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of stubble management (stubble retained vs. stubble removed) under contrasting tillage practices (no-tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) in Dingxi, Gansu, the northwestern Loess Plateau, China. Our results indicated that after 4 years small but significant changes in soil properties were observed amongst the different tillage and stubble treatments. Surface soil (0–5 cm) under no-tillage with stubble retention had the highest water stability of macroaggregates (>250 μm), soil organic carbon (SOC) and saturated hydraulic conductivity. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indicating the importance of the latter on soil structural stability. The improvement in soil structure and stability was confirmed by higher soil hydraulic conductivity measurements. Consistently higher K sat was detected in the no tillage with stubble retained soil compared to other treatments. Therefore, no-tillage with stubble retention practice is an effective management technique for improving physical quality of this fragile soil in the long term.

Effects of gravel–sand mulch, plastic mulch and ridge and furrow rainfall harvesting system combinations on water use efficiency, soil temperature and watermelon yield in a semi-arid Loess Plateau of northwestern China

Abstract In the northwestern Loess Plateau of China, low precipitation results in poor crop yields, with a great fluctuation from year to year. The adoption of gravel–sand mulching has shown improvements in the growth of crops such as watermelon. The ridge and furrow rainwater harvest system (RFRHS) has been shown as an easy and efficient way to collect rainwater. A field experiment was conducted from 2007 to 2009 at Gaolan, Lanzhou, Gansu, China, to measure the effects of RFRHS, plastic mulch and gravel–sand mulch combinations on soil temperature, evapotranspiration (ET), water use efficiency (WUE) and watermelon yield. There were eight treatments: (1) flat gravel–sand mulched field, (2) RFRHS with a sand mulched furrow, entire plastic mulch and the ratio 1:1 of ridge and furrow, (3) RFRHS with a sand mulched furrow, entire plastic mulch and the ratio 4:3 of ridge and furrow, (4) RFRHS with a sand mulched furrow, entire plastic mulch and the ratio 5:3 of ridge and furrow, (5) RFRHS with a sand and plastic mulched furrow, bare ridge and the ratio 4:3 of ridge and furrow, (6) RFRHS with an entire plastic mulch and the ratio 4:3 of ridge and furrow, (7) conventional ridge planting with a plastic mulched ridge, and (8) flat gravel–sand mulched field plus 23 mm supplementary irrigation. Soil temperature for RFRHS with a gravel–sand plus plastic mulched furrow was slightly lower than that of flat gravel–sand mulch. The RFRHS caused a significant increase in watermelon yield and WUE. The increase in watermelon yield and WUE was greatly influenced by the ratio of ridge and furrow when RFRHS was combined with gravel–sand mulch. Watermelon yield was highest for the 1:1 ratio, and WUE was highest for the 5:3 and 1:1 ratios of ridge:furrow, and these were significantly greater than that of flat gravel–sand mulch, without or with irrigation. The use of ridge with plastic film mulch increased the beneficial effect of RFRHS on yield. The watermelon yield and WUE for non-plastic-mulched ridge were even lower than that of flat gravel–sand mulch. In summary, the findings suggest that RFRHS with gravel–sand mulched furrow plus plastic film mulch, and 1:1 ratio of ridge:furrow, would facilitate the use of limited rainfall most efficiently in improving watermelon yield, by reducing ET and increasing WUE in this semiarid region.

Impacts of post-depositional processes on rapid monsoon signals recorded by the last glacial loess deposits of northern China

Rapid East Asian Monsoon oscillations recorded by Chinese loess are thought to be dynamically linked to north Atlantic climate. However, few efforts have been made to assess the effects of post-depositional processes (e.g., surface mixing and pedogenesis) on loess paleoclimatic records. Here a detailed optically stimulated luminescence dating of a thick loess sequence from the western Loess Plateau is presented, offering a reliable chronology for last glacial deposits. Magnetic susceptibility and mean grain size records from three loess–paleosol sequences along a northwest–southeast transect are investigated to evaluate impacts of post-depositional processes on these loess-based proxy records. Our results indicate that: (1) loess sequences developed within the flat tableland of the central and western Loess Plateau are nearly continuous during the last glaciation; and (2) post-depositional processes have distinct impacts on rapid monsoon signals recorded in loess sequences from different regions. In the central Loess Plateau, rapid monsoon signals have been attenuated to various degrees depending on the sedimentation rate and pedogenic intensity. In the northwestern Loess Plateau, however, due to high sedimentation rate and relatively weak pedogenesis, high-resolution grain size oscillations reliably record rapid monsoon changes and can be well correlated to rapid climate changes recorded in the Greenland ice core and Hulu cave stalagmite.

Effect of straw and plastic film management under contrasting tillage practices on the physical properties of an erodible loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and surface cover management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of straw and plastic film management under contrasting tillage practices (no tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) which had been under conventional management for hundred of years in the northwestern Loess Plateau, China. Surface soil (0–10 cm) under no tillage with straw cover had the highest water stability of macro-aggregates (>250 μm) and the highest saturated hydraulic conductivity. Compared with straw cover, plastic film cover did not change macro-aggregate stability and the soil had the lowest saturated hydraulic conductivity ( K sat) but the highest % <50 μm soil particles. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indication the importance of the latter on soil structural development. No tillage on its own (without straw cover) was not sufficient to improve structural stability probably due to lack of organic carbon input. While use of plastic film cover might lead to short term yield increases, results indicated that it did little to improve soil physical fertility. On the other hand, no tillage with straw cover management should lead to long-term improvement of physical quality of this structurally fragile soil.

Spatial and temporal patterns of Holocene vegetation and climate changes in arid and semi-arid China

Pollen data from 30 sites in arid and semi-arid regions of China were reviewed to document regional patterns of Holocene vegetation and climate change and to understand the large-scale controls on these changes. Vegetation at most sites in eastern Inner Mongolia switched between forest, forest steppe, and typical steppe, showing maximum moisture conditions before 6 ka (1 ka=1000 cal yr BP) and a dry climate after ∼6 ka. Vegetation in the northwestern Loess Plateau changed between desert steppe, forest steppe and steppe, suggesting wet–dry oscillations, from an initial dry to wet climate at ∼9–4 ka and then back to a dry climate. In the northern Tibetan Plateau, vegetation was characterized by steppe desert, steppe or desert, indicating a wet climate in the early and mid-Holocene until 6–4.5 ka. In western Inner Mongolia and Xinjiang, pollen assemblages show changes between desert, steppe desert and steppe, with a wet period occurring during 8.5–5.5 ka at most sites. All the four regions show a drying trend during the late Holocene. The complex climate patterns suggest that regional climate responses to large-scale climate forcing were controlled by interactions of competing factors, including the monsoons, westerlies and topography-induced regional atmospheric dynamics. The role of human activity in vegetation change requires further investigation.

Half-precessional cycles recorded in Chinese loess: response to low-latitude insolation forcing during the Last Interglaciation

Chinese loess offers favourable conditions for identifying evidence for high-resolution climatic changes. Previous studies have examined orbital scale climatic cycles and the other shorter time scale climatic oscillations, similar to the recorded glacial instability in deep-sea cores. In this study, we focus on examining the high-resolution palaeoclimatic records in the northwestern Loess Plateau, where the dust accumulation rate is high and the loess-soil sequences are highly sensitive to the shifting pattern of the East Asian monsoon system. Our results of magnetic susceptibility and particle size analysis from the northwestern Loess Plateau reveal well-defined half-precessional cycles during the last interglaciation, culminating at approximately 122,000, 111,000, 100,000, 88,000, and 79,000 yr. These variations are a direct response to the low-latitude forcing through its modulation on the East Asian summer monsoon. In this context, the East Asian summer monsoon has played an important role in conveying climatic signals from tropical Pacific to the middle latitude areas.