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土壤水稳性大团聚体测定方法综述   总被引:7,自引:0,他引:7       下载免费PDF全文
 湿筛法是测定土壤团聚体粒径分布和稳定性的经典方法。土样在湿润过程中,同时发生了崩解、差异膨胀和物理化学分散作用。已有的湿润方法按湿润速度可分为快速湿润和慢速湿润,按土样所处的气压条件可分为常压湿润和高真空湿润。常压快速湿润过程中,水分沿毛管快速渗入土体,土壤内部封闭的空气被压缩,产生微型爆炸,对团聚体破坏较大;慢速湿润和真空湿润能使团聚体稳定性显著增大。如果是为全面了解土壤团聚体稳定性及粒径分布的信息,可对土样采用常压快速湿润和常压慢速湿润(或真空湿润)2种预湿润。湿筛的作用在于区分不同粒级的土壤颗粒,应尽量减小对团聚体颗粒进一步的磨蚀作用,因此湿筛过程中振动速度不能太快。筛目可以根据实验目的选择。  相似文献
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Pedotransfer functions(PTFs) have been developed to estimate soil water retention curves(SWRC) by various techniques.In this study PTFs were developed to estimate the parameters(θ s,θ r,α and λ) of the Brooks and Corey model from a data set of 148 samples.Particle and aggregate size distribution fractal parameters(PSDFPs and ASDFPs,respectively) were computed from three fractal models for either particle or aggregate size distribution.The most effective model in each group was determined by sensitivity analysis.Along with the other variables,the selected fractal parameters were employed to estimate SWRC using multi-objective group method of data handling(mGMDH) and different topologies of artificial neural networks(ANNs).The architecture of ANNs for parametric PTFs was different regarding the type of ANN,output layer transfer functions and the number of hidden neurons.Each parameter was estimated using four PTFs by the hierarchical entering of input variables in the PTFs.The inclusion of PSDFPs in the list of inputs improved the accuracy and reliability of parametric PTFs with the exception of θ s.The textural fraction variables in PTF1 for the estimation of α were replaced with PSDFPs in PTF3.The use of ASDFPs as inputs significantly improved α estimates in the model.This result highlights the importance of ASDFPs in developing parametric PTFs.The mGMDH technique performed significantly better than ANNs in most PTFs.  相似文献
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Diversification of production is a concern for farmers in many regions of the world, raising a renewed interest in crop-animal rotations. However little information is available on whether the introduction of grazing animals in a no-till system could be a sustainable practice. The present long-term study was carried out in the semiarid region of Argentina, on an Entic Haplustoll (A, AC, C and Ck profile). The experimental plots were established in August 1993, with two treatments, no-till (NT) and conventional tillage (CT). Stubble was regularly used for grazing until 2002, when plots were divided into grazed (G) and non-grazed (NG) sub-treatments. Soil samples were taken at 0–0.10 and 0.10–0.20 m depth at the beginning of the experiment (1993) and during 2007, with the following determinations: clay + silt contents, bulk density (BD), total carbon (C), total nitrogen (N), available P, C contents of aggregate fractions of 2000–100 (POC), 100–50 (IOC) and <50 (FOC) μm diameter, aggregate size distribution and mean weight diameter change. NT showed a strong effect on all analyzed soil attributes: it had higher total carbon stocks (NT 16.6 Mg ha−1 vs. CT 13.2 Mg ha−1) and higher amounts in all C fractions, even in FOC (11.3 Mg ha−1 vs. 9.2 Mg ha−1). For BD, we found no difference between NT and CT at the surface and an even lower value for NT at 0.10–0.20 m depth. Under NT no depletion of available P occurred, while CT lost about 23 kg ha−1. Grazing had a negative effect on BD when averaging BD data across tillage systems, while there was no effect on aggregate stability, and a positive one on the proportion of >8 mm aggregates (23.3% vs. 11.7% for CT G and CT NG, respectively). C stratification showed a differential effect of grazing: NT G had the highest index (1.31) and CT G the lowest one (0.98). Our results indicated that the introduction of grazing animals in NT crop systems would not be detrimental to soil conditions and quality, at least in semiarid conditions of Argentina.  相似文献
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M. C. Ramos  S. Nacci  I. Pla 《CATENA》2003,53(4):365-376
A soil surface exposed to rainfall is subjected to processes of wetting and drop impact which can lead to the formation of a seal during the rainfall, reducing infiltration and increasing erosion by increasing runoff. The objective of this research was to evaluate the relationship between the effect caused by the drop impact and the aggregate stability of the soils when they are subjected to different disaggregation forces. The aggregates were subjected to cracking (by slow wetting), slaking (by fast wetting) and mechanical breakdown (by mechanical stirring after pre-wetting in ethanol). The effect of each process was evaluated by measuring the mean weight diameter (MWDsl, MWDf and MWDst, respectively) calculated as the sum of the mass fraction of soil left in the sieve after fractionation into four size classes, ranging from <0.25 to 2 mm, multiplied by the mean aperture of the sieve meshes and divided by the initial soil weight. The effect of water impact plus wetting was quantified by the saturated hydraulic conductivity of the seal (Ks) and the time necessary to reach this value. A relative sealing index (RSI) that measured the reduction of water intake caused by sealing was defined as the relationship between the minimum value of saturated hydraulic conductivity of the seal and that reached when the drop impact was avoided. The air-dry material rupture was evaluated with a penetrometer. The main soil characteristics that determine all these processes for the study soils were analysed. Most of the studied soils were very sensitive to slaking and mechanical breakdown, while they were stable when they were subjected to slow wetting. A significant relationship was found between the minimum saturated hydraulic conductivity (Ks) and the MWDst (R2=0.40, p<0.005), and between Ks and the MWDf (R2=0.69, p<0.05). In both treatments, slaking and mechanical stirring, the percentage of aggregates retained in the larger sieve mesh was also significantly correlated with Ks. This result could indicate that both processes are implicated in the disaggregation produced by drop impact, which contribute to seal formation process. The less stable soils had the lowest Ks value (<1 mm h−1), which was reached in a short period of time (<10 min). The high silt content and the low organic matter control the loss of aggregation by mechanical breakdown and the formation of the seal. The RSI values indicated a 200-fold reduction in water infiltration for some soils, caused by the formation of a seal.  相似文献
6.
Soils with high clay content are susceptible to structural damage, if they are intensively cultivated. The structure of soils of the Vertisol group has the tendency to restore as a result of wetting and drying. Samples of a remoulded clayey soil were exposed to seven successive wetting/drying (w/d) cycles, in order to study the change of some structural features of the newly formed aggregates. To assess the effect of soil water content and microbial activity, two different matric water potential ranges were used under sterile and non-sterile conditions.

Aggregate size distribution depended on both the water potential range and microbial activity and approached to a steady state with increasing cycle number. The water stability of the 2–1 mm aggregates was affected by the activity of soil micro-organisms under wet conditions and by forces of mechanical nature when the soil was reaching dryness. All cases resulted in aggregates of reduced water stability with respect to the natural aggregates. The <50 μm aggregated particles initially preserved stability, but after a number of w/d cycles they collapsed at a rate, depending mainly on the water potential range.  相似文献

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It has been suggested that liming can improve soil structure and thereby decrease losses of particles and associated nutrients. In this study, two types of structure lime, slaked lime (Ca(OH)2) and a mixed product of calcium carbonate (CaCO3) and slaked lime (Ca(OH)2), were applied at three different rates in field trials on clayey soils (23%–40% clay). A combination of primary tillage and structure liming was also studied, in a split-plot trial on a clayey soil (25% clay). Aggregate (2–5 mm) stability, measured as reduction in turbidity (which is strongly correlated with losses of particulate phosphorus), was significantly increased with the highest application rates of both structure lime products. Aggregate size distribution was also improved with structure lime, creating a finer tilth in the seedbed. Yield response to structure lime was not consistent, with both negative and positive responses over the four-year study period. Positive yield responses can possibly be attributed to the finer tilth preventing evaporation in two dry growing seasons. Negative yield responses were probably an effect of impaired phosphorus availability associated with limited precipitation in May-July in 2011 and 2013. Two years after liming, soil pH levels were significantly elevated in plots with the highest application rate of structure lime, whereas no significant increases were found three years after liming. However, a lingering effect of liming was still detectable, as manganese concentration in barley grain was significantly lower in plots with the highest application rates of both structure lime products in the fourth study year. These results indicate that structure liming can be used as a measure to mitigate phosphorus losses from clayey soils, thereby preventing eutrophication of nearby waters. However, the yield response was varying and unpredictable and thus further investigations are needed to determine the circumstances in which field liming can act efficiently not only to prevent phosphorus losses, but also to ensure consistent yield increases.  相似文献
9.
胡宇  蒋先军  田波  李航 《土壤》2007,39(6):964-967
在水田长期垄作免耕处理下,研究了土壤真菌多样性及其在不同大小团聚体中的分布.结果表明,垄作免耕处理下,耕层土壤中,真菌主要分布于粒级为1.0~0.25 mm的土壤团聚体中,同时在>0.053 mm的各级土壤团聚体中垄作免耕处理下真菌数量多于常规轮作处理;垄作免耕处理的各级土壤团聚体中都有毛霉和根霉存在,且1.0~0.25mm土壤团聚体中属类最丰富,其simpson多样性指数为0.93,Shannon多样性指数为1.24,常规轮作下属类丰度没有明显变化.稻田垄作免耕提高了不同团聚体中真菌的数量、多样性,改变了真菌在不同大小团聚体中的分布状况.  相似文献
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