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1.
Tillage stimulates soil carbon (C) losses by increasing aeration, changing temperature and moisture conditions, and thus favoring microbial decomposition. In addition, soil aggregate disruption by tillage exposes once protected organic matter to decomposition. We propose a model to explain carbon dioxide (CO 2) emission after tillage as a function of the no-till emission plus a correction due to the tillage disturbance. The model assumes that C in the readily decomposable organic matter follows a first-order reaction kinetics equation as: d Csail( t)/d t = − kCsoil( t) and that soil C-CO 2 emission is proportional to the C decay rate in soil, where Csoil( t) is the available labile soil C (g m −2) at any time ( t). Emissions are modeled in terms soil C available to decomposition in the tilled and non-tilled plots, and a relationship is derived between no-till ( FNT) and tilled ( FT) fluxes, which is: FT=a1FNT e−a2t, where t is time after tillage. Predicted and observed fluxes showed good agreement based on determination coefficient ( R2), index of agreement and model efficiency, with R2 as high as 0.97. The two parameters included in the model are related to the difference between the decay constant ( k factor) of tilled and no-till plots ( a2) and also to the amount of labile carbon added to the readily decomposable soil organic matter due to tillage ( a1). These two parameters were estimated in the model ranging from 1.27 and 2.60 ( a1) and −1.52 × 10 −2 and 2.2 × 10 −2 day −1 ( a2). The advantage is that temporal variability of tillage-induced emissions can be described by only one analytical function that includes the no-till emission plus an exponential term modulated by tillage and environmentally dependent parameters. 相似文献
2.
Soil puddling in advance of rice ( Oryza sativa L.) transplanting disperses surface aggregates and generates compaction at depth. As a management scheme for rice, puddling is typically considered advantageous for maximizing resource availability and yield. However, some experimental findings suggest a conflict between edaphic conditions created by this establishment technique and the performance of subsequent non-rice crops like wheat ( Triticum aestivum L.). At a site in the mid-hills region of Nepal on a silt loam soil with vertic characteristics, we compared the impact of six rice tillage (surface tillage—T 1, shank subsoiler—T 2, shank subsoiler + moldboard plough—T 3) and establishment (soil puddling + transplanting—TPR, direct seeding—DSR) combinations on soil physical properties over two cycles of the rice–wheat rotation. For the rice season, 0–20 cm saturated hydraulic conductivity ( Ksat) in the DSR plots was 2.6 and 4.3 times higher than their TPR counterparts in the first (Y 1) and second (Y 2) years, respectively (TPR-Y 1 = 93 mm day −1, DSR-Y 1 = 241 mm day −1, TPR-Y 2 = 133 mm day −1, DSR-Y 2 = 582 mm day −1), whereas tillage method did not significantly influence Ksat in this soil layer. The impact of rice establishment method was reflected in higher TPR bulk densities in the 5–10 (DSR = 1.19 g cm −3, TPR = 1.24 g cm −3) and 10–15 cm (DSR = 1.24 g cm −3, TPR = 1.29 g cm −3) depth increments in the wet season. Although none of the treatments significantly influenced the position or thickness of the plough sole, penetration resistance profiles suggest that vertical fractures with reduced soil strength were created within the pan region by deep tillage (T 2 and T 3), although these features were not associated with higher hydraulic conductivities from 20 to 50 cm. As the soils dried at the end of the rice season, crack propagation in the deep tilled plots (T 2 and T 3) was more pervasive. During the wheat season, comparable bulk density profiles and soil moisture retention characteristics across the treatments suggest that many of the edaphic changes induced by contrasting rice tillage and establishment practices did not persist in the self-mulching, vertic soils at our site. Conversely, significant increases in Ksat among the DSR plots from Y 1 to Y 2 (Y 1 = 241 mm day −1, Y 2 = 582 mm day −1) imply a temporal element to soil structural regeneration with adoption of direct seeding. 相似文献
3.
It is important to study the rate determining processes of chemical weathering and soil formation in volcanic islands since a significant part of the carbon fixed by chemical weathering of silicates on Earth is fixed at the surface of volcanic islands. These soils are fertile and much of the river suspended matter delivered to the ocean stems from these islands. This study determines the factors that drive the pedogenesis of a Histic Andosol in Western Iceland. Soil solutions were extracted from the profile in the field, from undisturbed ex situ mesocosms and from repacked laboratory microcosms. Concentrations of measured and calculated inorganic species in the field and experimental soil solutions were used for thermodynamic and kinetic interpretation, and to calculate the weathering rates. The main primary rock constituent of the 205 cm thick soil profile was basaltic glass, allophane content ranged from 2 to 22% and the soil carbon content ranged from 11 to 42%. Mean soil solution pH value ranged from 4 to 6 with the lowest value at 80 cm depth and highest between 150 to 205 cm. The high solute concentrations in soil solutions in the beginning of the microcosm weathering experiment declined faster for anions than cations. Under field conditions inorganic anions were supplied by marine and anthropogenic rather than pedogenic sources and hence these anions were subsequently leached out during the experimental duration when there was a limited input of anions through experimental precipitation. The factor, which defined the rate at which each ion was depleted from the exchange complex of the soil, decreased down the soil profile. The release sequence at 50 cm depth was Cl > Na > SO4 > F > Si. The Si and base cations experimental weathering rate when normalized to geographical surface area are similar to or lower than those measured from river catchments in Southwestern Iceland. The dissolved Al flux was much higher from the soil when compared to the river catchments. Field and experimental soil solutions were all highly undersaturated with respect to basaltic glass. Field and mesocosm samples were supersaturated with respect to secondary allophane and imogolite, while samples from the microcosms were often undersaturated with respect to allophane and imogolite. Predicted dissolution rate was dictated by the soil solution aH+3/aAl3+ activity ratio but slowed down by up to 20% and 30% by decreasing undersaturation in field and mesocosms respectively. Predicted dissolution rates according to the aH+3/aAl3+ activity ratio increased up to factor of 7, 30 and 37 by speciating Al3+ with oxalate in field, mesocosms and microcosms respectively. Speciation with oxalate, which represents the maximum effect of the dissolved organic carbon (DOC) on dissolution rates, generally had more effect near the surface than at deep levels in the soil profile. This study shows that at fixed temperature, reactive surface area, and composition of the volcanic glass in the soil, the chemical weathering rates of Andosols are dictated by: 1) aeolian deposition rates and drainage, which affect the saturation state and the aH+3/aAl3+ activity ratio, 2) the production of organic anions within the soil, and 3) external supply of anions capable of complexing Al3+. 相似文献
4.
选取河南西平杨树人工林生态系统中5种不同植物群落土地为研究对象,利用Licor-8100土壤呼吸测定系统对其土壤呼吸进行了连续观测,分析、比较5种不同植物群落土壤呼吸的差异及其影响因素。研究结果表明:（1）5种植物群落下土壤呼吸有所差异,但其日变化及年内变化趋势大致相同,均与土壤温度变化趋势一致,呈单峰曲线,其土壤呼吸大小顺序为:8 m行宽林间小藜—牛筋草地 > 2 m行宽林间苍耳地 > 8 m行宽林间水蓼—灰灰菜地 > 8 m行宽林间苍耳地 > 2 m行宽林间裸地;（2）采用土壤温度和湿度单因素模型（ Rs= ae bTs或 Rs=a W+b）进行分析:土壤温度和土壤含水量分别解释了不同植物群落土壤呼吸季节变化的41%~79%和2.3%~21%;而采用双因素模型分析（ Rs= ae bTsWc）,土壤温湿度共同解释了土壤呼吸速率季节变化的49.1%~86.7%,表明不同植物群落的土壤呼吸均受土壤温度和土壤含水量的共同影响;（3）运用 Q10=e 10b模型分析, Q10值大小顺序为:8 m行宽林间小藜—牛筋草地（2.47） > 2 m行宽林间苍耳地（2.3） > 2 m行宽林间裸地（2.7） > 8 m行宽林间水蓼—灰灰菜地（2.59） > 8 m行宽林间苍耳地（2.22）,且5种不同植物群落下土壤呼吸Q 10值均表现为春季 > 冬季 > 秋季 > 夏季,即土壤呼吸温度敏感性随着温度的升高呈现出降低的趋势。 相似文献
5.
Tillage affects the ability of coarse-textured soils of the southeastern USA to sequester C. Our objectives were to compare tillage methods for soil CO 2 flux, and determine if chemical or physical properties after 25 years of conventional or conservation tillage correlated with flux rates. Data were collected for several weeks during June and July in 2003, October and November in 2003, and April to July in 2004 from a tillage study established in 1978 on a Norfolk loamy sand (fine-loamy, kaolinitic, thermic Typic Kandiudults). Conventional tillage consisted of disking to a depth of approximately 15 cm followed by smoothing with an S-tined harrow equipped with rolling baskets. Conservation tillage consisted of direct seeding into surface residues. Flux rates in conservation tillage averaged 0.84 g CO 2 m −2 h −1 in Summer 2003, 0.36 g CO 2 m −2 h −1 in Fall 2003, 0.46 g CO 2 m −2 h −1 in Spring 2004, and 0.86 g CO 2 m −2 h −1 in Summer 2004. Flux rates from conventional tillage were greater for most measurement times. Conversely, water content of the surface soil layer (6.5 cm) was almost always higher with conservation tillage. Soil CO 2 flux was highly correlated with soil water content only in conventional tillage. In conservation tillage, no significant correlations occurred between soil CO 2 flux and soil N, C, C:N ratio, pH, bulk density, sand fraction, or clay fraction of the surface 7.5 cm. In conventional tillage, sand fraction was positively correlated, while bulk density and clay fraction were negatively correlated with soil CO 2 flux rate, but only when the soil was moist. Long-term conservation tillage management resulted in more uniform within- and across-season soil CO 2 flux rates that were less affected by precipitation events. 相似文献
6.
P sorption and desorption capacities were determined on 30 soil horizons (surface and subsurface) of soils with andic properties from the Azores, Portugal, using the Langmuir equation and successive extractions with dilute calcium chloride (CaCl 2), respectively. The proportion of P recovery (P rec) using distilled water (H 2O), CaCl 2, Bray 2 (B2), Mehlich 3 (M3), Egnér–Riehm (ER) and Olsen (OL) extractants was also determined to assess the extent of P release from soils enriched with P at P sorption maxima (P m). Soils containing very low amounts of organic C and allophane (Vitrandic Haplustepts and Vitrandic Udorthents) showed the lowest values of P m (48–565 mg kg − 1) and the highest values of P desorbability (P des) (69–100%), indicating that P can be easily lost from these soils. Application of fertilizers to these soils should be restrained in order to minimize eutrophication risk of nearby water bodies. In contrast, allophanic and non-allophanic horizons of Typic Placudands, Alic Hapludands, Acrudoxic Hapludands and Acrudoxic Hydrudands showed much higher values of P m (2273–52,400 mg kg − 1) and lower values of P des (4–57%).They also showed low proportions of P rec by the used extractants, indicating that large amounts of P can be sorbed in an unavailable form. Thus, these soils may require large amounts of P fertilizers and an efficient method of P application. Other studied soils with high amounts of 1:1 layer silicate minerals and having weak andic properties (Typic and Andic Haplustepts), showed intermediate P m (1124–8333 mg kg − 1) and P des values (20–63%). The values of Pm were positively correlated with Ald, Alo, allophane, Feo, Fed and Alp contents, and with the values of Alo + 1/2 Feo. In contrast, values of Pdes were negatively correlated with these soil constituents. Of the six extractants, the B2 extractant showed generally higher proportions of Prec than the other extractants in most studied soils. The proportions of Prec by the B2, M3, ER and OL extractants were negatively correlated with contents of Feo, Fed, Ald, Alo, Alp, and Fep, and with the values of Alo + 1/2 Feo and PR. 相似文献
7.
Asiatic diploid ( n = 13) cotton ( Gossypium arboreum L.) is grown on Vertisols of central India with limited amounts of fertilizers and pesticides under rainfed conditions. In an earlier study it was established that reduced tillage (RT) systems improved productivity of tetraploid ( n = 26) upland cotton ( G. hirsutum L.). Such information is currently not available for the Asiatic cotton. Field studies were continued from 2002–2003 through 2004–2005, to determine the effect of tillage systems on weed control, yield and fibre quality. Tillage treatments continued for 6 years before this phase of the study. The experiment was conducted in a split plot design, with three tillage systems as main plots and combination of species ( G. arboreum and G. hirsutum) and N rates (60 and 75 kg N ha −1) as subplots. Conventional tillage (CT) involved mouldboard ploughing + four to five inter-row cultivations and was compared with two levels of RT. RT 1 being pre-emergence herbicide application with two inter-row cultivations by a bullock drawn hoe and RT 2 was only herbicide application with no inter-row cultivation. Weed density (monocot and dicot weeds) was significantly lower on the RT than on the CT plots. Consequently, the RT plots had accumulated less weed dry matter. Seed cotton yield was affected by tillage systems in 1 out of 3 years. In 2002–2003, the yield trend was: RT 1 > CT > RT 2. The tillage × species interaction was significant in 2002–2003 and 2004–2005 and combined-across-years. Averaged over years, Asiatic G. arboreum produced 8% less seed cotton with treatment RT 2 than with CT. Upland, G. hirsutum produced 118–134 kg ha −1 additional seed cotton on the RT than with CT. Differences in maturity and rooting habit probably contributed to the two species differing in their tillage requirement. The Asiatic cottons were early maturing and are known to possess a deeper root system than the upland cotton. The tillage × N and species × N interactions were not significant. Average seed cotton yield with the 75 kg N was 15.7% more than the 60 kg N ha −1 plots. Among fibre properties, fibre length was significantly better with treatment RT 1 than with the CT in 2 out of 3 years. In summary, seed cotton yield of upland G. hirsutum cotton was higher with RT system, whereas converse occurred with G. arboreum. There were no adverse effects of RT on fibre quality. 相似文献
8.
为了明确不同成熟度油橄榄果实表观性状与内在品质的变化规律和相关性,以豆果、皮瓜尔、鄂植8号、莱星6个成熟度的果实为试验材料,对果实大小、颜色等8个表观指标以及含油率、脂肪酸组分、还原糖、总酚、总黄酮含量等内在品质指标进行测定,并对各指标间进行相关性分析。结果表明,4个品种油橄榄果实各指标随着成熟度的增加,呈现一定的变化规律,其中随着成熟度的增加,亮度值( L*值)、红绿值( a*值)、黄蓝值( b*值)均先增大后减小,横径增大,纵径变化不显著,横径增长速度大于纵径,果形指数变小,含油率升高,表明果实外观逐渐变圆;还原糖含量先降低后升高,总酚、总黄酮含量在第Ⅰ成熟度时显著高于其他5个成熟度,豆果、皮瓜尔、鄂植8号的饱和脂肪酸(SFA)、单不饱和脂肪酸(MUFA)与多不饱和脂肪酸(PUFA)比值越来越接近1∶1∶1。不同成熟度油橄榄的含油率与脂肪酸比值、还原糖、总酚含量、果形指数以及果实横径存在相关关系,且与 a*值、总黄酮含量呈极显著相关,相关系数最高分别为0.73、-0.84; a*值与还原糖含量呈显著负相关,与总酚、总黄酮含量极显著负相关;总黄酮含量与SFA、PUFA呈显著负相关,与总酚含量、MUFA、还原糖含量、果形指数、 L*值、 b*值呈显著正相关。综合变化规律和相关性分析结果认为,油橄榄果实 a*值和总黄酮含量可以代表大部分指标用于进行果实品质检测。本研究结果可为后续机械采收识别系统采集指标数据提供理论依据。 相似文献
9.
在北京九龙山自然保护区内选取有代表性的4种林分类型,测定各林分枯落物的蓄积量,采用室内浸泡法对其水文效应进行研究,旨在为该区森林植被枯落物生态水文功能评价提供一定的参考。结果表明:（1）4种林分枯落物层蓄积量大小依次为:黄栌油松混交林（29.65 t/hm 2） > 黄栌纯林（22.78 t/hm 2） > 黄栌侧柏混交林（16.87 t/hm 2） > 侧柏纯林（12.17 t/hm 2）;（2）同一浸水时间下黄栌油松混交林的枯落物持水量最大,黄栌纯林、黄栌侧柏混交林次之,侧柏纯林最小,枯落物层的持水量与浸泡时间为对数函数关系,持水量历时过程呈现出迅速吸水、缓慢吸水、逐渐饱和、饱和4个阶段;（3）4种林分枯落物层的吸水速率与浸水时间为幂函数关系,其过程可分为迅速下降、缓慢下降、趋于稳定的3个阶段。 相似文献
10.
Cultivation machinery applies large amounts of mechanical energy to the soil and often brings about a decrease in soil organic carbon (SOC). New experiments on the effects of mechanical energy inputs on soil respiration are reported and the results discussed. In the laboratory, a specific energy, K, of 150 J kg −1, similar to that experienced during typical cultivation operations, was applied to soil aggregates using a falling weight. Respiration (carbon dioxide, CO 2 emission) of the samples was then measured by an electrical conductimetric method. Basal respiration (when K=0) measured on Chromic Luvisol aggregates, was found to increase with increasing SOC, from 1.88 μg CO 2 g −1 h −1 for a permanent fallow soil (SOC=11 g kg −1) to 8.25 μg CO 2 g −1 h −1 for a permanent grassland soil (SOC=32 g kg −1). Basal respiration of a Calcic Cambisol, more than doubled (2.0–5.2 μg CO 2 g −1 h −1) with increasing gravimetric soil water contents. Mechanical energy inputs caused an initial burst of increased respiration, which lasted up to 4 h. Over the following 4–24 h period, arable soils with lower SOC contents, (11–21 g kg −1), respiration rates dropped back to a level, approximately 1.14 times higher than the basal value. However, grassland soils with higher SOC contents (28–32 g kg −1), increases in this longer-term respiration rate following 150 J kg −1 of energy, were negligible. A field experiment, in which CO 2 was measured by infra-red absorption, also showed that tillage stimulated increased levels of soil respiration for periods ranging from 12 h to more than one week. The highest respiration rates, 80 mg CO 2 m −2 h −1 were associated with high energy, powered tillage on clay soils. On the same soil, low energy draught tillage resulted in a respiration rate of approximately half this value. The results of these experiments are discussed in relation to equilibrium levels of soil organic matter. The application of known quantities of mechanical energy to soil aggregates under laboratory conditions, in order to simulate the effect of different cultivation practices, when combined with the subsequent measurement of soil respiration, can provide useful indication of the likely consequences of soil management on SOC. 相似文献
11.
采用凋落物分解网袋法对草海湿地流域森林优势植物青冈（ Cyclobalanopsisglauca）、桤木（ Alnus cremastogyne）和云南松（ Pinus yunnanensis）凋落物叶分解特性展开研究,揭示凋落物叶分解过程中自然持水率、最大持水率、最大拦蓄率、有效拦蓄率及凋落物持水率规律等。结果表明:（1）凋落物叶自然持水率随分解时间的增加呈先增后降趋势。凋落物叶自然持水率在分解历程中存在极显著性差异（青冈: F=213.79, P < 0.01;桤木: F=77.53, P < 0.01;云南松: F=179.12, P < 0.01）。（2）凋落物叶持水率（ Rt）与浸水时间（ t）呈显著正相关关系（ P < 0.05）,回归分析得到凋落物叶持水率（ Rt）与浸水时间（ t）符合对数函数方程 Rt= a+ bln t;凋落物叶持水速率（ v）与浸水时间（ t）呈显著负相关关系（ P < 0.05）,持水速率（ v）与浸水时间（ t）符合幂函数方程 v= at-b。（3）凋落物叶最大拦蓄率、有效拦蓄率随分解时间的推移,呈逐渐增加趋势。 相似文献
12.
On-line measurement of soil compaction is needed for site specific tillage management. The soil bulk density ( ρ) indicating soil compaction was measured on-line by means of a developed compaction sensor system that comprised several sensors for on-line measurement of the draught ( D) of a soil cutting tool (subsoiler), the soil cutting depth ( d) and the soil moisture content ( w). The subsoiler D was measured with a single shear beam load cell, whereas d was measured with a wheel gauge that consisted of a swinging arm metal wheel and a linear variable differential transducer (LVDT). The soil w was measured with a near infrared fibre-type spectrophotometer sensor. These on-line three measured parameters were used to calculate ρ, by utilising a hybrid numerical–statistical mathematical model developed in a previous study. Punctual kriging was performed using the variogram estimation and spatial prediction with error (VESPER) 1.6 software to develop the field maps of ρ, soil w, subsoiler d and D, based on 10 m × 10 m grid. To verify the on-line measured ρ map, this map was compared with the map measured by the conventional core sampling method. The spherical semivariogram models, providing the best fit for all properties was used for kriging of different maps. Maps developed showed that no clear correlation could be detected between different parameters measured and subsoiler D. However, the D value was smaller at shallow penetration d, whereas large D coincided with large ρ values at few positions in the field. Maps of ρ measured with the core sampling and on-line methods were similar, with correlation coefficient (r) and the standard error values of 0.75 and 0.054 Mg m−3, respectively. On-line measured ρ exhibited larger errors at very dry zones. The normal distribution of the ρ error between the two different measurement methods showed that about 72% of the errors were less than 0.05 Mg m−3 in absolute values. However, the overall mean error of on-line measured ρ was of a small value of 2.3%, which ensures the method accuracy for on-line measurement of ρ. Measurement under very dry conditions should be minimised, because it can lead to a relatively large error, and hence, compacted zones at dry zones cannot be detected correctly. 相似文献
13.
Over the last two decades, soil cultivation practices in the southern Argentinean Pampas have been changing from a 7 year cash-crop production system alternated with 2–3 years under pasture, to a continuous cropping system. A better understanding of the impact of the period of time a field has been under continuous cropping on a broad spectrum of soil properties related to soil quality is needed to target for sustainable cropping systems. The objectives of this study were to: (i) assess the relationship between physical and chemical soil parameters related to soil quality and (ii) identify soil quality indicators sensitive to soil changes under continuous cropping systems in the Argentinean Pampas. Correlation analysis of the 29 soil attributes representing soil physical and chemical properties (independent variables) and years of continuous cropping (dependent variable) resulted in a significant correlation (p < 0.05) in 78 of the 420 soil attribute pairs. We detected a clear relationship between hydraulic conductivity at tension h (Kh) and structural porosity (ρe); ρe being a simple tool for monitoring soil hydraulic conditions. Soil tillage practice (till or no-till) affected most of the soil parameters measured in our study. It was not possible to find only one indicator related to the years under continuous cropping regardless of the cultivation practice. We observed a significant relationship between years under continuous cropping and Kh under no-till (NT) and wheat fallow (p < 0.001, R2 = 0.70). Under these conditions, K−40 diminished as the number of years under continuous cropping increased. The change in mean weight diameter (CMWD) was the only physical parameter related to the number of years under continuous cropping, explaining 36% of the variability in the number of years under continuous cropping (p < 0.001) The combination of three soil quality indicators (CMWD, partial R2 = 0.38; slope of the soil water retention curve at its inflexion point (S), partial R2 = 0.14 and cation exchange capacity (CEC), partial R2 = 0.13) was able to explain, in part, the years under continuous cropping (R2 = 0.65; p value > 0.001), a measure related to soil quality. 相似文献
14.
[目的]理解和揭示深时古土壤的形成与演化有助于了解地球宜居性的形成与演化、促进土壤发生学理论的发展.[方法]以四川盆地晚中生代侏罗系和白垩系地层发育的古土壤为研究对象,通过对典型剖面的形态与微形态、矿物组成、颗粒组成以及地球化学等发生学特征的观察与分析,开展深时古土壤发生学特征与分类研究,并基于母质、气候、生物、地形和... 相似文献
15.
Woody plant proliferation in grasslands and savannas has been documented worldwide in recent history. To better understand the consequences of this vegetation change for the C-cycle, we measured soil microbial biomass carbon (C mic) in remnant grasslands (time 0) and woody plant stands ranging in age from 10 to 130 years in a subtropical ecosystem undergoing succession from grassland to woodlands dominated by N-fixing trees. We also determined the ratio of SMB-C to soil organic carbon (C mic/C org) as an indicator of soil organic matter quality or availability, and the metabolic quotient ( qCO 2) as a measure of microbial efficiency. Soil organic carbon (C org) and soil total nitrogen (STN) increased up to 200% in the 0–15 cm depth increment following woody plant invasion of grassland, but changed little at 15–30 cm. C mic at 0–15 cm increased linearly with time following woody plant encroachment and ranged from 400 mg C kg −1 soil in remnant grasslands up to 600–1000 mg C kg −1 soil in older (>60 years) woody plant stands. C mic at 15–30 cm also increased linearly with time, ranging from 100 mg C kg −1 soil in remnant grasslands to 400–700 mg C kg −1 soil in older wooded areas. These changes in C mic in wooded areas were correlated with concurrent changes in stores of C and N in soils, roots, and litter. The C mic/C org ratio at 0–15 cm decreased with increasing woody plant stand age from 6% in grasslands to <4% in older woodlands suggesting that woody litter may be less suitable as a microbial substrate compared with grassland litter. In addition, higher qCO 2 values in woodlands (0.8 mg CO 2-C g −1 C mic h −1) relative to remnant grasslands (0.4 mg CO 2-C g −1 C mic h −1) indicated that more respiration was required per unit of C mic in wooded areas than in grasslands. Observed increases in C org and STN following woody plant encroachment in this ecosystem may be a function of both greater inputs of poor quality C that is relatively resistant to decay, and the decreased ability of soil microbes to decompose this organic matter. We suggest that increases in the size and activity of C mic following woody plant encroachment may result in: (a) alterations in competitive interactions and successional processes due to changes in nutrient dynamics, (b) enhanced formation and maintenance of soil physical structures that promote C org sequestration, and/or (c) increased trace gas fluxes that have the potential to influence atmospheric chemistry and the climate system at regional to global scales. 相似文献
16.
The effects of wheel traffic on soil surface hydraulic properties, and consequent effects on erosion, following planting of vegetable crops in beds have not been widely studied. This paper describes two trials to quantify how wheel tracks influence infiltration and erosion rates, and assesses the value of cultivating wheel tracks for reducing erosion. The trials were carried out under natural rainfall, on Dystric Nitosols with clay loam texture and strong, stable structure. Net rates of erosion from onion ( Allium cepa L.) beds with cultivated or uncultivated inter-bed wheel tracks were measured with erosion pins and repeat topographic surveys of sediment trapped in silt fences. Infiltration rates in onion beds, cultivated and uncultivated wheel tracks, and changes in infiltration rates through winter, spring, and summer, were measured using the double-ring, ponded-water method. Differences in erosion rate were only measured in the second trial in which erosion rate from the uncultivated treatment was 21 Mg ha−1, compared to 1 Mg ha−1 for the cultivated treatment. Erosion occurred through mobilisation of soil along the edge and base of the wheel tracks, with no evidence of erosion of the onion beds. Most of the eroded soil comprised soil aggregates, with 75% between 0.25 and 4 mm in diameter, suggesting soil was transported in runoff along the wheel tracks as stable aggregates. Uncultivated wheel tracks had very low infiltration rates compared to onion beds and cultivated wheel tracks. The differences in infiltration rates between cultivated and uncultivated wheel tracks were consistent in both trials, with minor differences due to rainfall patterns and the implements used to cultivate wheel tracks. There were clear trends in infiltration rates through time, with rates in the uncultivated wheel tracks increasing during the growing season from 1.4×10−7 to 2.1×10−5 ms−1 and in onion beds from 1.1×10−4 to 2.5×10−4 ms−1, while rates in the cultivated wheel tracks decreased from 1.7×10−2 to 2.4×10−3 ms−1. The major increase of infiltration rate in uncultivated wheel tracks occurred after October when the soil surface began to dry out, and frequent wetting and drying cycles caused the compacted surface soil to crack. Most erosion occurred in the winter/early spring period when storm frequency and rainfall intensity was highest, and infiltration rates in the uncultivated wheel tracks lowest. Cultivating wheel tracks is a simple and effective practice to increase infiltration of rainfall and reduce erosion rates on clay-rich, strongly structured soils. 相似文献
17.
Tillage management can affect crop growth by altering the pore size distribution, pore geometry and hydraulic properties of soil. In the present communication, the effect of different tillage management viz., conventional tillage (CT), minimum tillage (MT) and zero-tillage (ZT) and different crop rotations viz. [(soybean–wheat (S–W), soybean–lentil (S–L) and soybean–pea (S–P)] on pore size distribution and soil hydraulic conductivities [saturated hydraulic conductivity ( Ksat) and unsaturated hydraulic conductivity { k( h)}] of a sandy clay loam soil was studied after 4 years prior to the experiment. Soil cores were collected after 4 year of the experiment at an interval of 75 mm up to 300 mm soil depth for measuring soil bulk density, soil water retention constant ( b), pore size distribution, Ksat and k( h). Nine pressure levels (from 2 to 1500 kPa) were used to calculate pore size distribution and k( h). It was observed that b values at all the studied soil depths were higher under ZT than those observed under CT irrespective of the crop rotations. The values of soil bulk density observed under ZT were higher in 0–75 mm soil depth in all the crop rotations. But, among the crop rotations, soils under S–P and S–L rotations showed relatively lower bulk density values than S–W rotation. Average values of the volume fraction of total porosity with pores <7.5 μm in diameter (effective pores for retaining plant available water) were 0.557, 0.636 and 0.628 m 3 m −3 under CT, MT and ZT; and 0.592, 0.610 and 0.626 m 3 m −3 under S–W, S–L and S–P, respectively. In contrast, the average values of the volume fraction of total porosity with pores >150 μm in diameter (pores draining freely with gravity) were 0.124, 0.096 and 0.095 m 3 m −3 under CT, MT and ZT; and 0.110, 0.104 and 0.101 m 3 m −3 under S–W, S–L and S–P, respectively. Saturated hydraulic conductivity values in all the studied soil depths were significantly greater under ZT than those under CT (range from 300 to 344 mm day −1). The observed k( h) values at 0–75 mm soil depth under ZT were significantly higher than those computed under CT at all the suction levels, except at −10, −100 and −400 kPa suction. Among the crop rotations, S–P rotation recorded significantly higher k( h) values than those under S–W and S–L rotations up to −40 kPa suction. The interaction effects of tillage and crop rotations affecting the k( h) values were found significant at all the soil water suctions. Both S–L and S–P rotations resulted in better soil water retention and transmission properties under ZT. 相似文献
18.
对辽东山地典型冰缘地貌上覆土壤的粒度、常微量化学元素进行测试分析,结果表明:土壤颗粒组成包括黏粒20.79%、粉粒69.54%和砂粒9.67%,平均粒径整体偏细,约为6.45Ф,不同土壤类型、地貌类型及坡向的粒度分布存在一定差异。土壤元素化学组成以SiO 2（45.60%）,Al 2 O 3（12.90%）,Fe 2O 3（3.90%）,K 2O （2.17%）为主,最大比例可达73.36%。元素Ca,Na,P,Sr显著淋溶,而Mn,Ti,Cu,Zn则相对富集,其他元素迁移不甚明显。少数元素还表现出与粒度分布存在显著关联,其中K,Na,Sr,Ba多存在于砂质土壤中,而元素Ti则容易在粒度更细致的黏土颗粒中留存。化学风化指数CIA均值约为65.50,Rb/Sr约为0.70,反映风化程度较低,且长期经历干冷气候,A—CN—K三角模型表明,研究区土壤风化以脱钙钠、富铝为主,风化水平尚处于低等风化阶段中后期。 相似文献
19.
Integrating livestock with cotton ( Gossypium hirsutum L .) and peanut ( Arachis hypogaea L.) production systems by grazing winter-annuals can offer additional income for producers provided it does not result in yield-limiting soil compaction. We conducted a 3-year field study on a Dothan loamy sand (fine-loamy, kaolinitic, thermic plinthic kandiudults) in southern Alabama, USA to determine the influence of tillage system prior to cotton–peanut planting on soil properties following winter-annual grazing. Two winter-annual forages [oat ( Avena sativa L.) and annual ryegrass ( Lolium mutiflorum L.)] and four tillage practices [chisel + disk, non-inversion deep tillage (paratill) with and without disking and no-till] were evaluated in a strip-plot design of four replications. We evaluated cone index, bulk density, infiltration, soil organic carbon (SOC), and total nitrogen (N). Paratilling prior to cotton or peanut planting, especially without surface soil tillage, reduced compaction initially to 40 cm and residually to 30 cm through the grazing period in winter. There were no significant differences in cone index, bulk density, or infiltration between forage species. No-tillage resulted in the greatest bulk density (1.65 Mg m −3) and lowest infiltration (36% of water applied), while paratilling increased infiltration in no-tillage to 83%. After 3 years, paratilling increased SOC 38% and N 56% near the soil surface (0–5 cm), as compared to concentrations at the beginning of the experiment, suggesting an improvement in soil quality. For coastal plain soils, integrating winter-annual grazing in a cotton–peanut rotation using a conservation tillage system of non-inversion deep tillage (paratill) with no surface tillage can improve soil quality by reducing cone index, increasing infiltration, and increasing SOC in the soil surface. 相似文献
20.
通过对盱眙月亮山5种人工林枯落物和土壤持水性能的研究,发现五种林下枯落物蓄积量为5.12~15.31 t/hm 2,最大持水率变化范围为164.09%~250.76%,最大持水量变化范围为8.40~41.18 t/hm 2,有效拦蓄量为3.55~28.12 t/hm 2,从大到小依次为杨树林 > 朴树林 > 桃树林 > 杨梅林 > 墨西哥柏林。不同林地类型林下枯落物持水量、吸水速率与浸水时间的动态变化规律基本相似,枯落物持水量随浸泡时间延长而增长,在水中浸泡24 h时,其持水量基本达到最大值,前2 h内各林分枯落物层持水作用较强。林下枯落物层持水量与浸泡时间之间的关系式为 Q= aln（ t）+ b,吸水速率与浸水时间之间的关系式为 V= ktn。杨树林地土壤的最大持水量和非毛管持水量均是最大,达到了305.24 t/hm 2,305.24 t/hm 2,并且杨树林地的渗透性能也是最好的。 相似文献
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