Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau,China

Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types(5 sites in grassland, 3 in woodland and 1 in shrubland) in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics(including root average diameter, root length density, root surface density and root biomass density), but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process(8–50 years).     

Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau,China

Knowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0–400 cm soil layer based on a long-term(2004―2016) experimental data in the northern Loess Plateau region, China. Soil bulk density(BD), saturated soil hydraulic conductivity(Ks), field capacity(FC) and soil organic carbon(SOC) in 2016, as well as the volumetric soil moisture content during 2004–2016, were measured in four vegetation types, i.e., shrubland(korshinsk peashrub), artificial grassland(alfalfa), fallow land and cropland(millet or potato). Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0–40 cm soil layer, and fallow land significantly increased FC and SOC in the 0–10 cm soil layer. Soil water storage(SWS) significantly declined in shrubland and grassland in the 40–400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland(alfalfa) and shrubland(peashrub) improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region.     

Effects of long-term fertilization on oxidizable organic carbon fractions on the Loess Plateau,China

The effects of long-term fertilization on pools of soil organic carbon(SOC)have been well studied,but limited information is available on the oxidizable organic carbon(OOC)fractions,especially for the Loess Plateau in China.We evaluated the effects of a 15-year fertilization on the OOC fractions(F1,F2,F3 and F4)in the 0–20 and 20–40 cm soil layers in flat farmland under nine treatments(N(nitrogen,urea),P(phosphorus,monocalcium phosphate),M(organic fertilizer,composted sheep manure),N+P(NP),M+N(MN),M+P(MP),M+N+P(MNP),CK(control,no fertilizer)and bare land(BL,no crops or fertilizer)).SOC content increased more markedly in the treatment containing manure than in those with inorganic fertilizers alone.F1,F2,F4 and F3 accounted for 47%,27%,18% and 8% of total organic carbon,respectively.F1 was a more sensitive index than the other C fractions in the sensitivity index(SI)analysis.F1 and F2 were highly correlated with total nitrogen(TN)and available nitrogen(AN),F3 was negatively correlated with p H and F4 was correlated with TN.A cluster analysis showed that the treatments containing manure formed one group,and the other treatments formed another group,which indicated the different effects of fertilization on soil properties.Long-term fertilization with inorganic fertilizer increased the F4 fraction while manure fertilizer not only increased labile fractions(F1)in a short time,but also increased passive fraction(F4)over a longer term.The mixed fertilizer mainly affected F3 fraction.The study demonstrated that manure fertilizer was recommended to use in the farmland on the Loess Plateau for the long-term sustainability of agriculture.     

绿肥填闲种植对旱作冬小麦农田土壤团聚体有机碳含量的影响

依托黄土塬区4 a绿肥填闲种植田间定位试验,开展不同填闲作物对土壤团聚体组成及各组分有机碳在团聚体中分布影响的研究,为阐明填闲种植措施下土壤有机碳库的物理保护机制提供依据。试验设置4个处理,即冬小麦夏闲期种植长武怀豆(SB)、苏丹草(SG)、怀豆/苏丹草混播(Mix)和裸地休闲(CK)。利用干筛法将全土筛分为>5 mm、2～5 mm、0.25～2 mm和<0.25 mm等4个粒级,分别测定土壤和各粒级团聚体中有机碳和颗粒有机碳含量,进而计算团聚体平均重量直径及有机碳贡献率。结果表明：绿肥种植对土壤团聚体分布有显著影响,各绿肥处理均有利于0～10 cm土层土壤团聚体的形成,但对亚表层土壤团聚结构影响较小。与CK相比,在0～40 cm各土层,SB、SG和Mix处理均显著提高土壤有机碳含量、颗粒有机碳含量及团聚体平均重量直径,提高幅度分别为7.9%、8.0%和7.9%,其中SB更有利于表层土壤有机碳的固存,且土壤有机碳和颗粒有机碳含量之间呈显著正相关关系,这两者与团聚体平均重量直径之间均呈显著负相关关系。不同处理下土壤团聚体各有机碳组分含量存在差异,与CK相比,SB和Mix均显著...     

Corn straw return can increase labile soil organic carbon fractions and improve water-stable aggregates in Haplic Cambisol

Corn straw return to the field is a vital agronomic practice for increasing soil organic carbon (SOC) and its labile fractions, as well as soil aggregates and organic carbon (OC) associated with water-stable aggregates (WSA). Moreover, the labile SOC fractions play an important role in OC turnover and sequestration. The aims of this study were to determine how different corn straw returning modes affect the contents of labile SOC fractions and OC associated with WSA. Corn straw was returned in the following depths: (1) on undisturbed soil surface (NTS), (2) in the 0-10 cm soil depth (MTS), (3) in the 0-20 cm soil depth (CTS), and (4) no corn straw applied (CK). After five years (2014-2018), soil was sampled in the 0-20 and 20-40 cm depths to measure the water-extractable organic C (WEOC), permanganate oxidizable C (KMnO₄-C), light fraction organic C (LFOC), and WSA fractions. The results showed that compared with CK, corn straw amended soils (NTS, MTS and CTS) increased SOC content by 11.55%-16.58%, WEOC by 41.38%-51.42%, KMnO₄-C and LFOC by 29.84%-34.09% and 56.68%-65.36% in the 0-40 cm soil depth. The LFOC and KMnO₄-C were proved to be the most sensitive fractions to different corn straw returning modes. Compared with CK, soils amended with corn straw increased mean weight diameter by 24.24%-40.48% in the 0-20 cm soil depth. The NTS and MTS preserved more than 60.00% of OC in macro-aggregates compared with CK. No significant difference was found in corn yield across all corn straw returning modes throughout the study period, indicating that adoption of NTS and MTS would increase SOC content and improve soil structure, and would not decline crop production.     

Long-term effects of gravel―sand mulch on soil organic carbon and nitrogen in the Loess Plateau of northwestern China

Gravel–sand mulch has been used for centuries to conserve water in the Loess Plateau of northwestern China. In this study, we assessed the influence of long-term(1996–2012) gravel–sand mulching of cultivated soils on total organic carbon(TOC), light fraction organic carbon(LFOC), microbial biomass carbon(MBC), total organic nitrogen(TON), particulate organic carbon(POC), mineral-associated organic carbon(MOC), permanganate-oxidizable carbon(KMn O4-C), and non-KMn O4-C at 0–60 cm depths. Mulching durations were 7, 11 and 16 years, with a non-mulched control. Compared to the control, there was no significant and consistently positive effect of the mulch on TOC, POC, MOC, KMn O4-C and non-KMn O4-C before 11 years of mulching, and these organic C fractions generally decreased significantly by 16 years. LFOC, TON and MBC to at a 0–20 cm depth increased with increasing mulching duration until 11 years, and then these fractions decreased significantly between 11 and 16 years, reaching values comparable to or lower than those in the control. KMn O4-C was most strongly correlated with the labile soil C fractions. Our findings suggest that although gravel–sand mulch may conserve soil moisture, it may also lead to long-term decreases in labile soil organic C fractions and total organic N in the study area. The addition of manure or composted manure would be a good choice to reverse the soil deterioration that occurs after 11 years by increasing the inputs of organic matter.     

不同耕作措施下陇中黄土高原旱作农田土壤活性有机碳组分及其与酶活性间的关系

通过设置在陇中黄土高原半干旱雨养农业区15年的不同保护性耕作措施长期定位试验,研究了传统耕作(T)、免耕(NT)、免耕结合秸秆覆盖(NTS)、传统耕作结合秸秆还田(TS)4种不同耕作措施下不同土层的土壤总有机碳、土壤活性有机碳、土壤微生物量、碳库管理指数和土壤蔗糖酶、淀粉酶、纤维素酶和过氧化物酶等4种参与碳循环土壤酶,并分析了土壤有机碳及其活性碳组分与土壤酶之间的相关关系。结果表明:0~30 cm土层,NTS处理可显著提高土壤有机碳、土壤活性有机碳、土壤微生物量碳及碳库管理指数,分别较T处理增加了16.3%、28.26%、41.88%、37.04%,NT、TS处理较T处理各指标也均有不同程度提高;在0~30 cm土层,NTS、TS、NT处理与T处理相比,蔗糖酶分别提高了33.84%、21.59%、25.15%,淀粉酶活性分别提高了20.90%、13.43%、12.69%,纤维素酶活性分别提高了39.13%、17.39%、4.34%,过氧化物酶活性分别提高了7.81%、2.08%、3.65%;土壤蔗糖酶、淀粉酶、纤维素酶、过氧化物酶与各形态有机碳及碳库管理指数均表现为显著或极显著正相关关系;蔗糖酶活性增加对有机碳积累作用最显著,有助于土壤总有机碳、活性有机碳、微生物量碳含量提高,土壤纤维素酶对土壤总有机碳和活性有机碳含量的增加有促进作用,过氧化物酶有利于总有机碳的积累。免耕结合秸秆覆盖是适宜该地区农田生态系统健康稳定发展,减少碳库损失的重要途径。     

黄土高原不同土壤类型有机碳密度与储量特征

土壤有机质的理化特性是黄土高原地区水土保持及生态修复的重要物质基础,充分了解黄土高原区不同土壤类型的有机碳密度与储量,对生态建设具有重要的实际意义。利用第二次全国土壤普查数据,对黄土高原不同土壤类型0～20 cm表层土体有机碳密度及储量进行估算,并分析两者的空间特征。结果表明：黄土高原区土壤有机碳密度加权平均值为2.00 kg·m-2,棕壤碳密度值最高,为15.56 kg·m-2,风沙土最低,仅为0.24 kg· m-2,空间上呈中间低四周高的分布格局。黄土高原地区总碳储量为1 239.85 Tg（1 Tg=1012 g）,灰褐土及黄绵土碳储量较高,两者占总体的46.86%,灰漠土、冻漠土、碱土较低,总量仅占0.17%,空间上呈由西北向东南递增的分布规律。黄绵土、风沙土在黄土高原区分布较广,但两者碳密度较低。因此,在今后的生态修复措施中,提高两者有机碳含量十分关键。     

Effects of different tillage and straw retention practices on soil aggregates and carbon and nitrogen sequestration in soils of the northwestern China

Soil tillage and straw retention in dryland areas may affect the soil aggregates and the distribution of total organic carbon. The aims of this study were to establish how different tillage and straw retention practices affect the soil aggregates and soil organic carbon (SOC) and total nitrogen (TN) contents in the aggregate fractions based on a long-term (approximately 15 years) field experimentin the semi-arid western Loess Plateau, northwestern China. The experiment included four soil treatments, i.e., conventional tillage with straw removed (T), conventional tillage with straw incorporated (TS), no tillage with straw removed (NT) and no tillage with straw retention (NTS), which were arranged in a complete randomized block design. The wet-sieving method was used to separate four size fractions of aggregates, namely, large macroaggregates (LA, >2000 μm), small macroaggregates (SA, 250-2000 μm), microaggregates (MA, 53-250 μm), and silt and clay (SC, <53 μm). Compared to the conventional tillage practices (including T and TS treatments), the percentages of the macroaggregate fractions (LA and SA) under the conservation tillage practices (including NT and NTS treatments) were increased by 41.2%-56.6%, with the NTS treatment having the greatest effect. For soil layers of 0-5, 5-10 and 10-30 cm, values of the mean weight diameter (MWD) under the TS and NTS treatments were 10.68%, 13.83% and 17.65%, respectively. They were 18.45%, 19.15% and 14.12% higher than those under the T treatment, respectively. The maximum contents of the aggregate-associated SOC and TN were detected in the SA fraction, with the greatest effect being observed for the NTS treatment. The SOC and TN contents were significantly higher under the NTS and TS treatments than under the T treatment. Also, the increases in SOC and TN levels were much higher in the straw-retention plots than in the straw-removed plots. The macroaggregates (including LA and SA fractions) were the major pools for SOC and TN, regardless of tillage practices, storing 3.25-6.81 g C/kg soil and 0.34-0.62 g N/kg soil. Based on the above results, we recommend the NTS treatment as the best option to boost soil aggregates and to reinforce carbon and nitrogen sequestration in soils in the semi-arid western Loess Plateau of northwestern China.     

Fractal features of soil profiles under different land use patterns on the Loess Plateau,China

Fractal theory is becoming an increasingly useful tool to describe soil structure dynamics for a better understanding of the performance of soil systems. Changes in land use patterns significantly affect soil physical, chemical and biological properties. However, limited information is available on the fractal characteristics of deep soil layers under different land use patterns. In this study, the fractal dimensions of particle size distribution(PSD) and micro-aggregates in the 0–500 cm soil profile and soil anti-erodibility in the 0–10 cm soil profile for 10 typical land use patterns were investigated in the Zhifanggou Watershed on the Loess Plateau, China. The 10 typical land use patterns were: slope cropland, two terraced croplands, check-dam cropland, woodland, two shrublands, orchard, artificial and natural grasslands. The results showed that the fractal dimensions of PSD and micro-aggregates were all significantly influenced by soil depths, land use patterns and their interaction. The plantations of shrubland, woodland and natural grassland increased the amount of larger micro-aggregates, and decreased the fractal dimensions of micro-aggregates in the 0–40 cm soil profile. And they also improved the aggregate state and aggregate degree and decreased dispersion rate in the 0–10 cm soil profile. The results indicated that fractal theory can be used to characterize soil structure under different land use patterns and fractal dimensions of micro-aggregates were more effective in this regard. The natural grassland may be the best choice for improving soil structure in the study area.     

Response of soil nitrogen,phosphorous and organic matter to vegetation succession on the Loess Plateau of China

 Revegetation is a traditional practice widely used for soil protection. We evaluated the effect of natural revegetation succession on soil chemical properties and carbon fractions (particulate organic carbon (POC), humus carbon (HS-C), humic acid carbon (HA-C) and fulvic acid carbon (FA-C)) on the Loess Plateau of China. The vegetation types, in order from the shortest to the longest enclosure duration, were: (a) abandoned overgrazed grassland (AbG3; 3 years); (b) Hierochloe odorata Beauv. (HiO7; 7 years); (c) Thymus mongolicus Ronnm (ThM15; 15 years); (d) Artemisia sacrorum Ledeb (AtS25; 25 years); (e) Stipa bungeana Trin Ledeb (StB36; 36 years) and (f) Stipa grandis P. Smirn (StG56; 56 years). The results showed that the concentrations of soil organic carbon, total nitrogen and available phosphorus increased with the increase of restoration time except for ThM15. The concentration of NH₄-N increased in the medium stage of vegetation restoration (for ThM15 and AtS25) and decreased in the later stage (for StB36 and StG56). However, NO₃-N concentration significantly increased in the later stage (for StB36 and StG56). Carbon fractions had a similar increasing trend during natural vegetation restoration. The concentrations of POC, HS-C, FA-C and HA-C accounted for 24.5%–49.1%, 10.6%–15.2%, 5.8%–9.1% and 4.6%–6.1% of total carbon, respectively. For AbG3, the relative changes of POC, HS-C and FA-C were significantly higher than that of total carbon during the process of revegetation restoration. The higher relative increases in POC, HS-C and FA-C confirmed that soil carbon induced by vegetation restoration was sequestrated by higher physical and chemical protection. The increases of soil C fractions could also result in higher ecology function in semiarid grassland ecosystems.     

Changes in aggregate-associated organic carbon and nitrogen after 27 years of fertilization in a dryland alfalfa grassland on the Loess Plateau of China

Changes in the distribution of soil aggregate sizes and concentrations of aggregate-associated organic carbon(OC) and nitrogen(N) in response to the fertilization of grasslands are not well understood. Understanding these changes is essential to the sustainable development of artificial grasslands. For understanding these changes, we collected soil samples at 0–20 and 20–40 cm depths from a semi-arid artificial alfalfa grassland after 27 years of applications of phosphorus(P) and nitrogen+phosphorus+manure(NPM) fertilizers on the Loess Plateau of China. The distribution of aggregate sizes and the concentrations and stocks of OC and N in total soils were determined. The results showed that NPM treatment significantly increased the proportions of 2.0 mm and 2.0–0.25 mm size fractions, the mean geometric diameter(MGD) and the mean weight diameter(MWD) in the 0–20 cm layer. Phosphorous fertilizer significantly increased the proportion of 2.0 mm size fractions, the MGD and the MWD in the 0–20 cm layer. Long-term application of fertilization(P and NPM) resulted in the accumulation of OC and N in soil aggregates. The largest changes in aggregate-associated OC and N in the 0–20 cm layer were found at the NPM treatment, whereas the largest changes in the 20–40 cm layer were found at the P treatment. The results suggest that long-term fertilization in the grassland leads to the accumulation of OC and N in the coarse size fractions and the redistribution of OC and N from fine size fractions to coarse size fractions.     

Responses of soil nitrogen,phosphorous and organic matter to vegetation succession on the Loess Plateau of China

Revegetation is a traditional practice widely used for soil protection. We evaluated the effect of natural revegetation succession on soil chemical properties and carbon fractions(particulate organic carbon(POC), humus carbon(HS-C), humic acid carbon(HA-C) and fulvic acid carbon(FA-C)) on the Loess Plateau of China. The vegetation types, in order from the shortest to the longest enclosure duration, were:(a) abandoned overgrazed grassland(Ab G3; 3 years);(b) Hierochloe odorata Beauv.(Hi O7; 7 years);(c) Thymus mongolicus Ronnm(Th M15; 15 years);(d) Artemisia sacrorum Ledeb(At S25; 25 years);(e) Stipa bungeana Trin Ledeb(St B36; 36 years) and(f) Stipa grandis P. Smirn(St G56; 56 years). The results showed that the concentrations of soil organic carbon, total nitrogen and available phosphorus increased with the increase of restoration time except for Th M15. The concentration of NH4-N increased in the medium stage(for Th M15 and At S25) and decreased in the later stage(for St B36 and St G56) of vegetation restoration. However, NO3-N concentration significantly increased in the later stage(for St B36 and St G56). Carbon fractions had a similar increasing trend during natural vegetation restoration. The concentrations of POC, HS-C, FA-C and HA-C accounted for 24.5%–49.1%, 10.6%–15.2%, 5.8%–9.1% and 4.6%–6.1% of total carbon, respectively. For Ab G3, the relative changes of POC, HS-C and FA-C were significantly higher than that of total carbon during the process of revegetation restoration. The higher relative increases in POC, HS-C and FA-C confirmed that soil carbon induced by vegetation restoration was sequestrated by higher physical and chemical protection. The increases of soil C fractions could also result in higher ecological function in semiarid grassland ecosystems.     

退耕年限与方式对土壤团聚体稳定性及有机碳分布的影响

以黄土高原南部退耕还林年限6 a(FL06)和15 a(FL15)刺槐林地、退耕还草年限6 a(GL06)和15 a(GL15)紫花苜蓿草地为研究对象,以临近长期耕作坡耕地(CK)作为对照,采用湿筛法,分离出2 mm、1~2 mm、0.5~1 mm、0.25~0.5 mm和0.25 mm 5个粒级的水稳性团聚体,研究了退耕年限与方式对团聚体稳定性和不同粒径团聚体有机碳分布的影响。结果表明:在0~20 cm土层,退耕还林还草与未退耕相比能显著提高2 mm和1~2 mm粒径团聚体含量,显著减少0.25 mm粒径团聚体含量,其中对于2 mm和1~2 mm粒径团聚体在不同退耕年限与方式下含量表现为GL15GL06FL06FL15CK和GL15FL06GL06FL15CK;退耕还林和还草增加了两个土层的团聚体稳定性,GL15的平均重量直径(MWD)值和几何平均直径(GMD)值均最大,土壤结构最稳定,其次为GL06;不同退耕年限,2 mm粒径下退耕还林地和还草地、1~2 mm粒径下退耕还草地团聚体有机碳含量均随退耕年限的延长而增加。20~40 cm土层中,团聚体含量均值随粒径的减小而增加;MWD和GMD值均小于0~20 cm层;各粒径范围内退耕还林与还草后的团聚体有机碳含量与坡耕地相比总体表现出减小的趋势。研究结果表明,退耕改善了土壤结构,对各粒径团聚体有机碳含量分布的影响随退耕年限与方式不同效应各异,且GL15相较于其它退耕年限和方式下的样地有更好的土壤团聚体稳定性和更多的团聚体有机碳积累。     

黄土高原丘陵沟壑区不同土地利用的土壤养分特征

以黄土高原丘陵沟壑区第3副区典型流域为研究区,采用实地调查、土壤采样分析和数理统计相结合的方法,基于33个样点的土壤养分数据,研究了林地、草地、果园、梯田、坡耕地5种土地利用的土壤养分特征。结果表明：土地利用方式对黄土高原丘陵沟壑区典型流域土壤有机质、全N和速效P含量的影响达到显著水平,对其他养分指标影响不明显。土壤有机质和全N含量从高到低依次为：林地＞坡耕地≈梯田＞果园＞草地,林地明显高于其他土地利用类型,而草地土壤养分最差。速效P含量从高到低依次为：果园、坡耕地、梯田、林地和草地,农业耕作植被下的速效P含量明显高于自然生态植被。研究表明：梯田作为传统的水土保持措施,在研究区具有良好的土壤保肥作用,而分布于陡坡的草地,养分保持效果在5种土地利用中最差。     

土地利用方式对东祁连山土壤表层有机碳的影响

在祁连山东段高寒地区,选取天然草地、退耕自然恢复地、坡耕地和人工草地4种土地利用方式,研究了土地利用方式对土壤表层有机碳含量和有机碳密度的影响.结果表明:在4种土地利用方式中天然草地土壤表层有机碳含量最高,坡耕地和退耕自然恢复地土壤表层有机碳含量较低;土壤表层有机碳密度整体上随着土层加深而逐渐降低,在0～30cm土层土...     

陇东黄土高原土地利用、覆盖变化及驱动力分析

从土地利用和土地覆被的角度出发，利用RS和GIS技术，分析了20世纪最后15a该区土地利用和土地覆被变化在数量、结构和类型上的特点，并进一步分析了该区土地利用／土地覆被变化的驱动力，得出以下结论。15a间除建设用地和草地面积增加外，其他土地利用类型都呈现出不同程度减少。其中耕地减少了20691hm^2，主要转变为建设用地，且减少的耕地多为位置相对优越。产量较高的优质良田；林地减少了12269hm^2，主要转变为草地、早地和建设用地；草地的面积增加了33488hm^2，主要源自干林地和耕地的变化；交通建设用地高速增长，15a间增加了9278．8hm^2。该区土地利用和土地覆被变化的驱动力主要为自然因素、人口压力、经济因素及宏观政策等。     

长期秸秆和地膜覆盖对旱作冬小麦农田土壤碳组分的影响

地表覆盖秸秆和地膜是我国西北旱作农田土壤固碳的重要田间管理措施,但其对土壤碳组分的长期影响尚不明确。基于田间定位试验,设生育期高量秸秆覆盖(9 000 kg·hm^-2,HSM)、生育期低量秸秆覆盖(4 500 kg·hm^-2,LSM)、夏闲期秸秆覆盖(9 000 kg·hm^-2,FSM)、生育期地膜覆盖(PM)和无覆盖对照(CK)共5个处理,研究了秸秆覆盖和地膜覆盖12 a和13 a后旱作冬小麦农田土壤总有机碳(SOC)、颗粒有机碳(POC)、潜在矿化碳(PCM)和微生物量碳(MBC)含量的变化规律。2 a平均结果表明：与CK相比,HSM和LSM处理均显著提高了0～10 cm土层各碳组分含量以及10～20 cm土层SOC、POC、MBC含量,同时还显著提高了0～20 cm土层POC和MBC占SOC的比例;而FSM和PM处理对各土层土壤碳组分含量及其占SOC的比例均无显著影响。土壤碳组分含量相互之间均存在极显著正相关关系。综上可知,长期生育期秸秆覆盖能有效提高旱作冬小麦农田耕层土壤有机碳及其组分含量,且提高覆盖量有助于促进...     

黄土塬区土地利用变化对深剖面土壤水分的影响

在长武塬区的6个地点分别采集农地、10年果园和20年果园10 m深剖面的土样,通过测定和分析不同样地的土壤水分,定量揭示其对土地利用变化的响应。结果表明:农地和10年果园土壤水分具有相似的垂向分布,随深度增加土壤水分含量增大,而20年果园随深度增加呈减小趋势,但6 m以下3种样地土壤水分随深度增加基本不发生变化;农地、10年和20年果园在0~6 m、6~10 m和0~10 m土层平均土壤水分含量分别为17.8%、17.5%和15.8%,20.4%、20.6%和14.8%,18.8%、18.7%和15.4%,与农地相比,20年果园0~6m、6~10m和0~10 m土层减少的土壤水分分别占农地的11%、27%和18%;农地6~10 m土壤储水量为1 063 mm,而转化为果园后随果龄增大而减小,其中10年果园无明显差异,但20年果园减少了291 mm,在该土层形成稳定的低湿层。20年果园6 m以下稳定的低湿层可能减少水分的深层渗漏进而降低地下水补给量,伴随着大面积的农地转化为人工林草,可能会对区域水循环造成影响。     

The impact of land use change on soil organic carbon and labile organic carbon stocks in the Longzhong region of Loess Plateau

Land use change (LUC) is widely recognized as one of the most important driving forces of global carbon cycles. The soil organic carbon (SOC) and labile organic carbon (LOC) stores were investigated at arable land (AL), artificial grassland (AG), artificial woodland (AW), abandoned arable land (AAL) and desert steppe (DS) in the Longzhong region of the Loess Plateau in Northwest China. The results showed that conversions from DS to AL, AL to AG and AL to AAL led to an increase in SOC content, while the conversion from DS to AW led to a decline. The differences in SOC content were significant between DS and AW at the 20-40 cm depth and between AL and AG at the 0-10 cm depth. The SOC stock in DS at the 0-100 cm depth was 39.4 t/hm 2 , increased by 28.48% after cultivation and decreased by 19.12% after conversion to AW. The SOC stocks increased by 2.11% from AL to AG and 5.10% from AL to AAL. The LOC stocks changed by a larger magnitude than the SOC stocks, which suggests that it is a more sensitive index of carbon dynamics under a short-term LUC. The LOC stocks increased at 0-20 cm and 0-100 cm depths from DS to AW, which is opposite to that observed for SOC. The proportion of LOC to SOC ranged from 0.14 to 0.20 at the 0-20 cm depth for all the five land use types, indicating low SOC dynamics. The allocation proportion of LOC increased for four types of LUC conversion, and the change in magnitude was largest for DS to AW (40.91%). The afforestation, abandonment and forage planting on arable land led to sequestration of SOC; the carbon was lost initially after afforestation. However, the carbon sink effect after abandonment may not be sustainable in the study area.