~(137)Cs示踪采煤沉陷坡土壤侵蚀及其对土壤养分的影响

为更好地理解矿区土壤退化机理,该文利用137Cs技术研究了焦作矿区具有15a沉陷历史的采煤沉陷坡土壤侵蚀特征及其对土壤养分的影响。沉陷坡137Cs含量从坡顶到下坡逐渐降低,及至坡脚急剧增大且表现出最高的值。基于137Cs本底(1 645 Bq/m2),沉陷坡坡顶至下坡表现为土壤侵蚀,而坡脚为土壤沉积。沉陷坡土壤侵蚀高达3.75 kg/(m2·a),属于中度侵蚀。沉陷坡土壤黏粒含量沿下坡方向增加,表明水蚀的分选性搬运。与对照区相比,沉陷坡侵蚀区土壤总有机碳(total organic carbon,TOC)、水溶性有机碳(water-soluble organic carbon,WSOC)、全氮、碱解氮、全磷、有效磷含量均出现了显著降低(P0.05);沉积区除WSOC显著降低(P0.05)外,其他养分含量变化不明显(P0.05)。在沉陷坡的侵蚀区,TOC与WSOC含量沿下坡方向逐渐减小,表现出与137Cs一致的分布格局;其他养分含量的坡面变化与137Cs分布不一致。相较于对照区,WSOC/TOC与碳氮比、碳磷比在沉陷坡侵蚀强烈的坡位分别出现了显著增大与降低(P0.05)。研究结果表明:1)焦作矿区自采煤沉陷坡形成以来发生了较严重的水蚀;2)侵蚀引起的土壤再分配影响沉陷坡土壤碳、氮、磷动态,其中,土壤再分配对土壤碳动态的影响最强;3)在土壤侵蚀作用下,采煤沉陷坡侵蚀强烈的坡位土壤有效态碳、氮、磷养分潜在的侵蚀风险大。采煤沉陷坡土壤侵蚀及其对土壤养分的不利影响应引起矿粮复合区土地整治的关注。     

渭北旱塬侵蚀退化土壤生产力的恢复与评价

土壤侵蚀会降低生产力,威胁农业生产,因此,对土壤生产力进行恢复和评价具有重要意义。通过人工剥离熟土层,模拟研究不同侵蚀程度下的土壤生产力,选取施肥和覆盖表土2种恢复措施,对其土壤生产力的恢复情况展开研究并进行评价。结果表明:1)土壤侵蚀能够使土壤的理化性状恶化,施肥和覆土均能很好地改善土壤密度和孔隙度等,并能够增加土壤有机质及其他养分的质量分数。2)土壤侵蚀会降低作物产量,在不施肥下,每侵蚀1cm熟土层,玉米产量平均下降1.27%,施肥下每侵蚀1 cm熟土层,玉米产量比对照平均增加0.87%;而每覆盖1cm熟土层,玉米产量平均增加0.91%,但并不能完全补偿侵蚀造成的产量损失。3)利用土壤生产力指数模型(PI模型)计算出了不同措施下的生产力指数,发现:无肥下侵蚀的生产力指数最低,平均每侵蚀1 cm熟土层,生产力指数下降2.17%,施肥下平均每侵蚀1 cm熟土层,生产力指数比无肥增加1.09%,而平均每覆盖1 cm熟土,生产力指数增加1.29%;表明覆土较施肥更易提高土壤生产力。4)对产量和生产力指数进行相关性分析,得出二者具有很好的正相关关系,说明用生产力指数来衡量土壤生产力的高低是可行的。     

南方红壤丘陵区土壤侵蚀-沉积作用对土壤酶活性的影响

土壤酶与土壤矿质营养元素循环、能量转移等密切相关。明确土壤酶对土壤侵蚀—沉积作用的响应机制,有助于进一步把握土壤侵蚀在全球碳循环中的作用。通过分析湘中红壤丘陵区松林坡面侵蚀区及沉积区土壤酶活性的变化特征,揭示了酶活性与土壤主要养分因子之间的关系,并在此基础上深入探讨了土壤侵蚀—沉积作用对土壤酶活性的影响。结果表明:沉积区绝大多数土层土壤有机碳(soil organic carbon,SOC)、全氮(total nitrogen,TN)、可溶性有机碳(dissolved organic carbon,DOC)、脲酶、酸性磷酸酶及过氧化氢酶活性均要显著高于侵蚀区。土壤沉积作用明显提高了土壤养分含量及酶活性。其次,侵蚀区与沉积区土壤养分含量及酶活性差异在侵蚀干扰较为严重的表层(0~30 cm)土壤表现较为明显,随着土壤深度的增加差异逐渐减小。侵蚀区与沉积区SOC、TN、DOC及酶活性均随土壤深度的增加呈现总体下降的趋势。相关性分析表明,土壤脲酶、酸性磷酸酶、过氧化氢酶之间及其与SOC、TN、DOC之间均存在极显著正相关关系(p0.01)。此外,偏冗余分析结果进一步表明SOC是解释土壤酶活性动态变化的主要因子,其解释量达7.5%,侵蚀诱导SOC在坡面的再分布是影响土壤酶活性的重要途径之一。     

Influence of simulated erosion on soil properties and maize yield in Northwestern India

Abstract

Laboratory and field experiments were conducted at the Regional Research Station of Kandi Area, Ballowal Saunkhri, Punjab, India, to determine the immediate influence of artificial topsoil removal (simulated erosion) on selected soil properties, maize (Zea mays) growth and yield, and restoration of crop productivity with nitrogen (N) fertilization. For the laboratory experiment, soil samples (0–15 cm) were obtained after removing 0, 6, 12, and 18 cm of a sandy loam topsoil from a cereal grain cropped field. In the field experiment, topsoil was removed at 0, 6, 12, and 18 cm in main plots, and six N treatments at rates of 0, 40, 80, 120, 160, and 200 kg N ha^‐1 were applied in subplots. Topsoil removal greatly decreased mineralized N, N mineralization potential and rate constant, and increased time for half mineralization of N. Bulk density and penetration resistance increased as a result of topsoil removal and infiltration capacity of the soil decreased. Total profile water was more at the time of harvest than at sowing in the plots where topsoil was removed, but the water expense efficiency decreased. Both grain and straw yield of maize decreased substantially as a result of adverse effect of topsoil removal on plant height, mass and depth of root, length and girth of cob, and thousand grain weight. Nitrogen application improved maize growth and yield, but the crop responded to higher doses of N on eroded plots than the uneroded plots, and yields on eroded plots did not match to those obtained on uneroded plots at any level of N application. In conclusion, artificial surface soil erosion deteriorated soil properties governing maize productivity. More N was required where topsoil had been eroded, but N application alone did not restore crop yield to that level obtained from uneroded soil. Therefore, there is a need to look for and quantify other factors also to improve soil productivity.     

黑土区典型坡耕地土壤酶活性空间分布特征研究

基于对松花江流域东山沟小流域坡耕地表层0-20 cm土壤酶活性和养分含量分析,研究了东北黑土区典型坡耕地土壤酶活性空间分布特征及其影响因素.结果表明,小流域下游的土壤转化酶、脲酶、碱性磷酸酶活性均高于流域上游和中游;坡面侵蚀区3种土壤酶活性均低于坡面沉积区;土壤酶活性沿坡长分布呈现坡顶较高—坡中低—坡下高的变化趋势,与坡面土壤侵蚀强度相对应.3种土壤酶活性之间呈极显著相关关系.土壤酶活性空间分布特点与土壤侵蚀强度空间分布趋势呈现相一致的规律,表明土壤侵蚀降低了土壤酶活性.     

Loss of soil resources from water‐eroded versus uneroded cropland sites under simulated rainfall

Soil erosion is widespread in agricultural lands of the US Corn Belt. The objective of this study was to examine the impact of antecedent erosion on loss of soil under laboratory simulated rainfall. The soil was obtained from the surface layer of eroded (ER) and uneroded (UN) sites within a conservation agro‐ecosystem in central Ohio, USA. Air‐dried soil was subjected to a rainfall simulation for 60 min (dry run), and to another simulation (wet run) 24 h after the dry run. In the dry run, the cumulative water runoff, sediment yield, and soil organic carbon loss were higher in ER (12.3 L/m², 169.3 g/m², and 5.6 g/m², respectively) than in the UN (7.3 L/m², 22.6 g/m², and 0.9 g/m² respectively). An opposite trend was observed for the cumulative water infiltration (0.9 and 3.9 L/m², respectively). In the wet run, despite a similar cumulative water runoff from the two erosional phases (20.1 and 19.6 L/m² in ER and UN respectively), sediment yield and soil organic carbon loss were higher in ER (484.4 g/m², and 16.3 g/m² respectively) than in the UN (146.6 g/m², and 5.3 g/m² respectively). Also for the wet run, an opposite trend was observed for the cumulative infiltration (0.8 and 5.8 L/m² respectively). This study suggests that past erosional processes increase the susceptibility of remaining soil to accelerated erosion.     

整地时期对东北雨养区土壤含水量及玉米产量的影响

以东北雨养区春玉米农田为研究对象,分析春季和秋季2个整地时期对农田土壤含水量、土壤物理性状、土壤养分含量以及玉米产量等的影响。结果表明:秋整地可显著提高玉米产量,与春整地相比增产8.7%(P<0.05)。秋整地处理下土壤水分状况得到显著改善,播种前和苗期耕层土壤(0-20cm)含水量分别比春整地高18.9%和5.6%。整地时期对种子层土壤(0-10cm)的物理特性影响不明显(P>0.05),但秋整地可显著改善10-40cm的根层土壤物理性状,其中土壤孔隙度比春整地平均提高10.0%,而土壤容重则比春整地平均下降11.6%。整地时期对0-40cm层次的土壤硬度和土壤养分含量影响不显著。可见,秋整地主要通过改善土壤物理蓄水性能和减少水分散失提高土壤水分含量,保证较高的成株率和成穗率,进而利于玉米高产稳产。     

Manure and nitrogen fertilizer effects on corn productivity and soil fertility under drip and furrow irrigation

A field experiment was conducted at the Arkansas Valley Research Center in 2005 through 2007 to study the effects of manure and nitrogen fertilizer on corn yield, nutrient uptake, N and P soil tests, and soil salinity under furrow and drip irrigation. Manure or inorganic N was applied in 2005 and 2006 only. There were no significant differences in corn yield between drip and furrow irrigation even though, on average, 42% less water was applied with drip irrigation. Inorganic N or manure application generally increased grain yield, kernel weight, grain and stover N uptake, and grain P uptake. Nitrogen rates above 67 kg ha^?1 did not increase grain yield significantly in 2005 or 2006, nor did manure rates in excess of 22 Mg ha^?1. High manure rates increased soil salinity early in the season, depressing corn yields in 2005 and 2006, particularly with drip irrigation. Salts tended to accumulate in the lower half of the root zone under drip irrigation. Residual nitrate nitrogen from manure and inorganic N application sustained corn yields above 12.0 Mg ha^?1 in 2007. More research is needed to develop best manure and drip irrigation management for corn production in the Arkansas Valley.     

Stability of organic matter in soils of the Belgian Loess Belt upon erosion and deposition

Soil erosion has significant impacts on terrestrial carbon (C) dynamics. It removes C‐rich topsoil and deposits it in lower areas, which might result in its stabilization against microbial decay. Subsequently, C‐poor deeper horizons will be exposed, which also affects C stabilization. We analysed factors governing soil organic C (SOC) mineralization in topsoil (5–10 cm) and subsoil (75–100 and 160–200 cm) horizons from two contrasting sites (up‐slope compared with down‐slope) in the Belgian Loess Belt; we refer to these as eroding and depositional sites, respectively. Deposition of eroded soil material resulted in significantly increased SOC contents throughout the entire soil profile (2 m) and microbial biomass C in the topsoil. In a 28‐day incubation experiment we studied effects of O₂ concentrations (0, 5 and 20%) and substrate (glucose) availability on C mineralization, soil microbial biomass and CaCl₂‐extractable C. Carbon enrichment at the depositional site was accompanied by weak mineralization rates and small contents of water‐extractable organic C. Addition of glucose stimulated microbial growth and enhanced respiration, particularly in the subsoil of the depositional site. Availability of O₂ showed the expected positive relationship with C mineralization in topsoils only. However, small O₂ concentrations did not decrease C mineralization in subsoils, indicating that controls on C dynamics were different in top‐ and subsoils. We conclude that reduced C mineralization contributed to C accumulation as observed at depositional sites, probably because of poor availability of C in subsoil horizons. Limited availability of O₂ in subsoils can be excluded as an important control of soil C accumulation. We hypothesize that the composition of the microbial community after burial of the organic‐rich material might play a decisive role.     

Long‐term fertilization impacts on corn yields and soil organic matter on a clay‐loam soil in Northeast China

A long‐term fertilization experiment with monoculture corn (Zea mays L.) was established in 1980 on a clay‐loam soil (Black Soil in Chinese Soil Classification and Typic Halpudoll in USDA Soil Taxonomy) at Gongzhuling, Jilin Province, China. The experiment aimed to study the sustainability of grain‐corn production on this soil type with eight different nitrogen (N)‐, phosphorus (P)‐, and potassium (K)–mineral fertilizer combinations and three levels (0, 30, and 60 Mg ha^–1 y^–1) of farmyard manure (FYM). On average, FYM additions produced higher grain yields (7.78 and 8.03 Mg ha^–1) compared to the FYM0 (no farmyard application) treatments (5.67 Mg ha^–1). The application of N fertilizer (solely or in various combinations with P and K) in the FYM0 treatment resulted in substantial grain‐yield increases compared to the FYM0 control treatment (3.56 Mg ha^–1). However, the use of NP or NK did not yield in any significant additional effect on the corn yield compared to the use of N alone. The treatments involving P, K, and PK fertilizers resulted in an average 24% increase in yield over the FYM0 control. Over all FYM treatments, the effect of fertilization on corn yield was NPK > NP = NK = N > PK = P > K = control. Farmyard‐manure additions for 25 y increased soil organic‐matter (SOM) content by 3.8 g kg^–1 (13.6%) in the FYM1 treatments and by 7.8 g kg^–1 (27.8%) in the FYM2 treatments, compared to a 3.2 g kg^–1 decrease (11.4%) in the FYM0 treatments. Overall, the results suggest that mineral fertilizers can maintain high yields, but a combination of mineral fertilizers plus farmyard manure are needed to enhance soil organic‐matter levels in this soil type.     

Soil degradation by erosion

Soil degradation by accelerated erosion is a serious problem and will remain so during the 21st century, especially in developing countries of the tropics and subtropics. Yet, its extent, severity, and economic and environmental impacts are debatable. Estimates of global and regional land area affected are tentative and subjective. Results of field measurements are often technique‐dependent. Considerable progress has been made in modeling soil erosion, yet field validation of these models remains to be done for principal soils and ecoregions. Similar to the land area affected, estimates of erosional impacts on crop yield, productivity and soil quality are tentative and subjective. Further, erosion‐induced losses on crop yield are scale‐dependent because of the compensatory beneficial effects on yields from depositional sites, and technology‐dependent because of the masking effects of input such as fertilizers and irrigation. Erosion caused changes in soil carbon dynamics and non‐point source water pollution are important environmental impacts. While erosion (e.g., detachment and transport) can lead to emission of trace gases into the atmosphere, deposition can bury and sequester some of the carbon. In addition to improving the database on the land area affected, there is also a need to assess erosional impacts on productivity and soil C balance at the watershed, regional, and global scale. Copyright © 2001 John Wiley & Sons, Ltd.     

贵州坡耕地三种种植模式的水土保持效果对比研究

通过研究紫花苜蓿—玉米间作、作物分带轮作和玉米单作3种种植模式下地表覆盖度和表层土壤含水量月变化,年均土壤和养分流失量以及产量等,比较不同模式的水土保持效果。结果表明:紫花苜蓿—玉米间作与分带轮作模式可保持坡耕地全年覆盖,并在整个雨季保持较高的覆盖度。紫花苜蓿根系发达,增加了0—20cm耕层土壤中的根量,增强了土壤的渗透能力,保护了生物多样性,可减少地表径流39.3%,减少土壤侵蚀59.3%;分带轮作可减少地表径流10.4%,减少土壤侵蚀21.3%;两种模式都提高了雨季前和雨季耕层土壤中的水分,减少了水土流失引起的有机质流失29.9%～52.4%,全N流失26.7%～54.9,全钾流失27.3%～70.9%,缓效钾流失21.4%～58.9%,提高玉米产量33.0%～35.9%;紫花苜蓿—玉米间作还可收获紫花苜蓿干草13 664kg/hm2,复合产量是农民习惯的4.1倍;分带轮作可收获大豆、红薯、油菜等,复合产量为12 492kg/hm2,是农民习惯的2.7倍。     

Impact of soil redistribution in a sloping landscape on carbon sequestration in Northeast China

Soil organic carbon (SOC) in eroded soil can be redistributed from upper slope positions and deposited and sequestered in depressional areas. However, the SOC lost from soil erosion is normally not considered when soil carbon budgets are derived and this could result in an overestimation of SOC loss from the agricultural areas. The impact of soil redistribution on the SOC budget of a sloping landscape in the Black soil region in Northeast China was studied using the presence of the ¹³⁷Cs tracer which has been deposited since 1954 and the fly‐ash tracer, which was deposited in 1903. Five landscape positions (summit, shoulder‐, back‐, foot‐ and toe‐slope) were selected and included in this study. The depths of ¹³⁷Cs and fly ash and the SOC content of the deposition layers were used to calculate the change in C content of the soil in the various landscape positions over the last century. We found that the most severe soil erosion occurred in soils in the shoulder‐slope position followed by the back‐slope and the summit positions. Soil deposition occurred in the toe‐slope position followed by the foot‐slope position. A total of 683 kg C was eroded from the summit, shoulder‐ and back‐slopes (in a 1 m wide strip) over the past 100 years and 418 kg C (about 61·2 per cent) was deposited in the low‐lying areas (foot‐ and toe‐slopes). Over half (61·5 per cent) of the deposition (257 kg SOC) occurred over the past 50 years. Most of the previously reported loss of C from the upper slope positions in the Black soils was in fact sequestered in the deposition areas in the landscape. Copyright © 2005 John Wiley & Sons, Ltd.     

模拟玉米茎秆流对土壤侵蚀的影响

玉米茎秆流是降雨过程中经玉米冠层截留后沿茎秆流向根部的水量,是种植坡地地表径流的重要组成部分,对植物根部的土壤侵蚀过程具有重要影响。采用人工模拟降雨方法,研究了成熟期玉米茎秆流对坡地土壤侵蚀的影响。试验土槽长为0.40 m、宽为0.23 m、深为0.14 m;采用直径为2 cm的PVC管模拟成熟期玉米茎秆,高度为1.2 m;模拟茎秆流量为5,10,15 g/s,用相同降雨条件下无茎秆流坡地作为对照措施;降雨强度为60,90,120 mm/h,降雨历时108 min,坡度为10°。结果表明:(1)与对照措施相比,茎秆流具有加快坡地地表产流的作用;(2)模拟茎秆流条件下地表产流量和产沙量均高于对照,相较无茎秆流坡地,3个降雨强度下各茎秆流量的产流贡献率为14.90%~43.10%,产沙贡献率为12.47%~26.75%;(3)茎秆流在茎秆周围地表形成细小股流,促使坡地土壤侵蚀过程由面蚀向细沟侵蚀转变,从而增加了坡地土壤侵蚀量。因此,在坡地水土流失计算与评价中应考虑茎秆流的土壤侵蚀作用。     

子午岭地区林地破坏加速侵蚀对土壤养分流失和微生物的影响研究

以浅沟集水区为研究对象,分析了子午岭地区林地被开垦破坏15年后裸露地在不同侵蚀强度和侵蚀方式下的土壤养分流失和土壤微生物数量的变化。结果表明,林地开垦破坏后,土壤侵蚀加剧发展,侵蚀强度达159.7t/(hm2a),是林地土壤侵蚀量的上千倍。开垦破坏15年后,裸露地浅沟集水区不同地形部位表层土壤全氮、有机碳、速效磷和土壤微生物总数显著减少,同林地相比,依次分别减少37.9%～82.6%、42.7%～86.4%、24.2%～80.3%和31.8%～92.0%。在裸露地浅沟集水区梁坡随坡长的增加,表层土壤有机碳、全氮和速效磷含量及微生物总数呈显著的下降趋势,且沟槽的土壤各养分含量及微生物总数明显低于沟间。裸露地浅沟集水区土壤养分流失强度及微生物数量减少幅度在浅沟集水区的空间分布与土壤侵蚀方式和侵蚀强度相对应。林地开垦破坏15年后,土壤养分以有机碳流失最严重,其次分别为速效磷、全氮;微生物中的真菌减少幅度最大,细菌次之,放线菌减少幅度最小。     

基于RUSLE模型的孙水河流域土壤侵蚀空间分异特征

土壤侵蚀一直是我国开展区域生态环境治理所关注的热点问题之一。在RS和GIS技术支持下,基于RUSLE模型分析了凉山州孙水河流域不同土地利用类型、海拔和坡度条件下土壤侵蚀强度的特征,定量评价了研究区土壤侵蚀空间特征。结果表明:孙水河流域平均土壤侵蚀模数为1 954.32 t/(km~2·a),土壤侵蚀严重区域主要集中于孙水河干流及其支流沿岸;坡耕地和中覆盖草地是流域内主要侵蚀土地利用类型;海拔2 000～3 000 m流域土壤侵蚀较为严重,平均土壤侵蚀模数超过2 000 t/(km~2·a);当坡度低于25°时,土壤侵蚀模数随着坡度的增加而增大,15°～25°是该流域侵蚀最为严重的地带。研究成果可服务于凉山州孙水河流域水土保持治理工作,为实现乡村振兴提供一定理论支持。     

Immediate effects of topsoil removal on crop productivity loss and its restoration with commercial fertilizers

A field experiment was conducted on a Typic Cryoboroll (Site 1) and a Typic Cryoboralf (Site 2) in north-central Alberta, Canada, to determine the influence of simulated erosion (artificial topsoil removal) on loss in yield of hard-red spring wheat (Triticum aestivum L. cv. ‘Roblin'), and to determine to which extent fertilizers N and P will restore the lost crop productivity of two artificially-eroded soils. There were three depths of topsoil removal (0, 10, and 20 cm) as main plot treatments, and a factorial combination of four levels of N (0, 50, 100, and 150 kg N ha⁻¹) and three levels of P (0, 9, and 18 kg P ha⁻¹) as sub-plot treatments. Wheat yields at both sites were markedly reduced by increasing depth of topsoil removal. The erosion effects were more pronounced at Site 2 where average yield on the 20 cm cut decreased to less than half of that obtained under non-eroded conditions. At both sites, additions of fertilizer N and P to eroded soil increased wheat yield, but the yields did not match those obtained in non-eroded soil under the same fertilizer treatment. Plants growing on eroded soil responded differently to application of fertilizers N and P, not only in terms of yield but also in N and P concentration and uptake. The implication of these findings is that fertilization programs for fields with varying degree of erosion would require optimization of rates so as to restore yield and, at the same time, minimize nutrient losses (e.g., N leaching) and improve soil tilth.     

中国南方红壤丘陵马尾松林下侵蚀坡面的土壤特性

[目的]探清土壤侵蚀对土壤分布与特性的影响机制,为防治该地区的林下水土流失和土地退化提供科学依据。[方法]基于调查取样和分析测试获取的数据,采用统计和灰色关联度等方法分析红壤丘陵区马尾松林地侵蚀坡面的土壤特性。[结果]红壤丘陵区马尾松林地侵蚀坡面土壤养分相对较低,理化指标基本处于4级以下水平;红壤丘陵区马尾松林地侵蚀沟的土壤指标与坡面土壤的相应指标存在显著性差异,18个土壤指标中,侵蚀沟的土壤有10个指标显著优于坡面土壤的相应指标,侵蚀沟与土壤特性关联度更高,侵蚀沟土壤指标间的显著相关数量更少。[结论]红壤丘陵区马尾松林地的土壤侵蚀对林下土壤特性和分布产生了显著的影响,但侵蚀沟对土壤特性的影响机制尚需进一步研究。     

Soil organic carbon and fly-ash distributions in eroded phases of soils in Illinois and Russia

Soil organic carbon (SOC) dynamics are affected by tillage, soil erosion and depositional processes. The objectives of this paper are to evaluate soil organic carbon and fly-ash distribution methods for identifying eroded phases of soils in Illinois and Russia and quantifying the extent of soil loss from erosion. The effect of accelerated erosion on soils is recorded on National Cooperative Soil Survey maps as phases of soil series that reflect the percentage of the original A horizon materials remaining. Identification depends on knowledge of the original A horizon thicknesses, SOC and fly-ash contents at uncultivated and uneroded sites when determining erosion phases of soil at cultivated and eroded sites. However, locating uncultivated and uneroded comparison sites with similar landscape and slope characteristics can be difficult. The amount of A horizon materials within the plow layers (Ap horizons) or topsoils are often determined by soil colors which reflect the SOC contents. Soil erosion phases based on original A horizon materials remaining in the topsoils may underestimate the extent of soil losses from topsoils and subsoils, particularly where soils have been cultivated for hundreds of years and are severely eroded. The SOC contents and soil erosion phases can be affected by losses or gains of organic C-rich sediments from tillage translocation and erosion, by management input level differences, oxidation, or as a result of land use and landscape position variations. Fly-ash was found to be more stable and act as a better indicator of soil erosion phase than SOC content.     

加速土壤侵蚀对养分流失的影响

Soil erosion and nutrient losses on newly-deforested lands in the Ziwuling Region on the Loess Plateau of China were monitored to quantitatively evaluate the effects of accelerated soil erosion, caused by deforestation, on organic matter, nitrogen and phosphorus losses. Eight natural runoff plots were established on the loessial hill slopes representing different erosion patterns of dominant erosion processes including sheet, rill and shallow gully （similar to ephemeral gully）. Sediment samples were collected after each erosive rainfall event. Results showed that soil nutrients losses increased with an increase of erosion intensity. Linear relations between the losses of organic matter, total N, NH4-N, and available P and erosion intensity were found. Nutrient content per unit amount of eroded sediment decreased from the sheet to the shallow gully erosion zones, whereas total nutrient loss increased. Compared with topsoil, nutrients in eroded sediment were enriched, especially available P and NH4-N. The intensity of soil nutrient losses was also closely related to soil erosion intensity and pattern with the most severe soil erosion and nutrient loss occurring in the shallow gully channels on loessial hill slopes. These research findings will help to improve the understanding of the relation between accelerated erosion process after deforestation and soil quality degradation and to design better eco-environmental rehabilitation schemes for the Loess Plateau.