沙坡头地区土壤结皮形成机理的研究

本文通过大量的事实和依据论述了结皮形成的物质来源和结皮的形成与土壤性质的关系，表明了粉粒（０．０５－０．０１ｍｍ）含量是结皮形成的关键，并从结皮的发育过程、剖面变化、地理位置和养分含量等方面说明了粉粒的分选和聚积过程，进而论述了粉粒的累积机理、结皮的形成过程及结皮形成－破碎的动态变化。     

Release, movement and recovery of 3,4-dimethylpyrazole phosphate (DMPP), ammonium, and nitrate from stabilized nitrogen fertilizer granules in a silty clay soil under laboratory conditions

 The composition of soil microbiota in four heated (350  °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g^–1 soil or 3.0 μg chlorophyll a g^–1 soil) with cyanobacteria (Oscillatoria PCC9014, Nostoc PCC9025, Nostoc PCC9104, Scytonema CCC9801, and a mixture of the four) was studied by cultural methods. The aims of the work were to investigate the potential value of cyanobacteria as biofertilizers for accelerating soil recolonization after fire as well as promoting microbiotic crust formation and to determine the microbial composition of such a crust. The inoculated cyanobacteria proliferated by 5 logarithmic units in the heated soils which were colonized very quickly and, after 2 months of incubation, the cyanobacterial filaments and associated fungal hyphae made up a matrix in which surface soil particles were gathered into crusts of up to 1.0 cm in thickness. These crusts were composed, on average, of 2.5×10¹⁰ cyanobacteria, 2.8×10⁶ algae, 6.1×10¹⁰ heterotrophic bacteria (of which 1.2×10⁸ were acidophilic, 1.3×10⁶ were Bacillus spp. and 1.5×10⁸ were actinomycetes) and 77.8 m fungal mycelium (1.4×10⁶ were fungal propagules) g^–1 crust. Counts of most microbial groups were positively correlated to cyanobacterial numbers. The efficacy of treatment depended on both the class of inoculum and the type of soil. The best inoculum was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone; however, the latter was comparatively the most favoured by the amendment. In the medium term there were no significant differences between the two inocula rates used. Biofertilization increased counts of cyanobacteria by 8 logarithmic units while heterotrophic bacteria, actinomycetes, algae and fungal propagules rose by >4 logarithmic units, acidophilic bacteria and Bacillus spp. by around 3 logarithmic units and fungal mycelia showed an 80-fold increase. The results showed that inoculation of burned soils with particle-binding diazotrophic cyanobacteria may be a means of both improving crust formation and restoring microbial populations. Received: 8 March 2000     

Wind erosion from crusted playa surfaces by no saltation and with saltation: A comparison through laboratory wind tunnel experiments

Playas are common in many arid regions and recognized as a major source of hypersaline particles. A better understanding of wind erosion on crusted playas has significant implications for land management and pollution control practices. We hypothesized that wind erosion rates of crusted playas were complicated and controlled by the interactions between playa crust and wind-induced saltation conditions. However, comparisons regarding the effects of different playa crusts on wind erosion under no saltation (NS) and with saltation (WS) conditions were lacking. In this study, laboratory wind tunnel experiments were carried out to simulate both NS and WS conditions, to investigate the erosion rates of different crust types (Salt, Takyr, and Puffic crust) at different wind speeds. Results showed that: 1) Salt crust had greater crust strengths than did Takyr crust and Puffic crust; 2) wind erosion rates under the WS condition were up to 60 times greater than those under the NS condition, suggesting that sand bombardment was the dominant mechanism responsible for removal of fine material from crusted playa surfaces; 3) both sand bombardment rate and wind erosion rate of the playa crusts increased with increasing wind speed under the WS conditions; 4) Puffic crust exhibited a greater rate of wind erosion compared to both the Takyr and Salt crusts under the NS condition, yet tended to have a lower rate of wind erosion compared to both the Takyr and Salt crusts under the WS condition. This difference can be attributed to the fact that soft Puffic crusts are pliable and can dissipate the force of impacting grains under the WS conditions. Our results indicated that wind erosion processes on crusted playas are complicated and are affected by wind-induced saltation and crust type, specifically crust strength and elasticity of the surface.     

Effects of biological soil crusts on soil enzyme activities in revegetated areas of the Tengger Desert,China

Biological soil crusts (BSCs) cover up to 70% of the sparsely-vegetated areas in arid and semiarid regions throughout the world and play a vital role in dune stabilization in desert ecosystems. Soil enzyme activities could be used as significant bioindicators of soil recovery after sand burial. However, little is known about the relationship between BSCs and soil enzyme activities. The objective of this study was to determine whether BSCs could affect soil enzyme activities in revegetated areas of the Tengger Desert. The results showed that BSCs significantly promoted the activities of soil urease, invertase, catalase and dehydrogenase. The effects also varied with crust type and the elapsed time since sand dune stabilization. All the soil enzyme activities tested in this study were greater under moss crusts than under cyanobacteria–lichen crusts. The elapsed time since sand dune stabilization correlated positively with the four enzyme activities. The enzyme activities varied with soil depth and season, regardless of crust type. Cyanobacteria–lichen and moss crusts significantly enhanced all test enzyme activities in the 0–20 cm soil layer, but negatively correlated with soil depth. All four enzyme activities were greater in the summer and autumn than in spring and winter due to the vigorous growth of the crusts. Our study demonstrated that the colonization and development of BSCs could improve soil quality and promote soil recovery in degraded areas of the Tengger Desert.     

Emergence of irrigated cotton in flatland planting in relation to furrow opener type and crust-breaking treatments for Cambisols in central Iran

Emergence of cotton (Gossypium hirsutum L.) under flatland mechanized planting system with crust-forming soil and saline soil and irrigation water can be suboptimal in central Iran. A field experiment was conducted to determine furrow opener type and crust-breaking method effects on cotton emergence on a silty clay soil (Calcic Cambisols). The effects of five planters (equipped with runner, single- and double-disk type openers) and five crust-breaking methods (using rolling cultivator, rolling-type crust breaker, spike-tooth, chain-type harrows and no crust-breaking) on the seedling emergence were studied. The results showed that planter type significantly affected cotton seedling emergence. In non-crust-breaking method, the best emergence was produced with the double-disk opener planter that created crack lines along the seed rows. This phenomenon was not observed with the runner-type opener planter. However, some crack lines were observed on the outside edges of its smooth-crown zero-pressure press wheels tires, which resulted in large clod formation after crust-breaking and had therefore negative effect on seedling emergence. Crust-breaking had negative effect on final emergence for double-disk planter due to filling the crack lines with loosened soil. Crust-breaking improved emergence percentages for runner opener planters, when the depth of penetration of the crust breaker teeth was shallow. The conclusion is that irrigated cotton emergence on crust-forming soils in a flatland planting system might significantly be improved by selecting a double-disk planter with zero-pressure press wheel tires without any crust-breaking operation under the soil and climate of central Iran.     

Microbiotic Crust Influence on Unsaturated Hydraulic Conductivity

Microbiotic crusts occur extensively in rangeland soils . Developed by filaments of cyanobacteria and algae , and thalli of lichen and moss entanglement of soil particles , they create a physical discontinuity in the surface profile with greater concen trations of clay , silt , and potentially hydrophobic organic matter. These conditions potentially contribute to variability in soil hydrology of arid land and should be considered in the development of hydrologic and erosion models. However, there is limited manipulative research examining the functional relationships between soil and microbiotic crusts . We investigated the influence of cyanobacterial-dominated microbiotic crust on measured hydraulic conductivity (K) in a sandy loam soil at a southeastern Utah site . Using a tension infiltrometer , we determined K under three surface treatments: undisturbed , chemically killed (representing dead microphytes within the crust), and removed (scalped) microbiotic crusts. We applied treatments to spatially interspersed intact surface soils within shrub interspaces . Microbiotic crusts at this site and in this stage of successional development had no discernible influence on K. This finding supports results from research conducted in a variety of soils from sandy to silt dominated with a range of microbiotic development . Because this research was site and time specific , and because the role of microbiotic crusts in the environment continues to be debated , additional research is warranted to deter mine how stage of development of microbiotic crust influences soil hydrology .     

Kinetics of crust formation during conventional French bread baking

64 breads were baked in a deck oven under conventional French baking conditions. Their hearth and surface temperatures were measured at various baking times using thermocouples and Infra-red thermometer; their moisture content was determined after sampling of the external layer, termed the “crust”, and by weighing breads. In addition, an image analysis method, based on saturation and colors, allowed determination of a mask of crust and the kinetics of its mean thickness. Associated with hydrothermal kinetics, it showed that the development of crust was achieved at a final local temperature of 160 °C and moisture of 5% for an average final thickness of 1.7 mm. DSC analysis of crust samples also underlined the significance of non gelatinized starch in the crust. This result was interpreted by representing the hydrothermal history of crust in a starch melting diagram.     

Effect of vegetation cover on the hydrology of reclaimed mining soils under Mediterranean-Continental climate

Vegetation cover plays a major role in the restoration and stabilization of disturbed systems. The analysis of relationships between restored vegetation and soil hydrology has special relevance for the evaluation and operation of mining reclamation, particularly in Mediterranean-Continental environments, where climatic conditions restrict the development of continuous vegetation cover. The effect of herbaceous vegetation cover on soil hydrology was analysed by means of rainfall simulation (63 mm h^− 1; 0.24 m²) in reclaimed soils derived from opencast coal mining (a non-saline and clay-loam textured spoil) in central-eastern Spain. A total of 75 simulation experiments were conducted at three different times throughout the year (late winter, summer and autumn) to control the influence of seasonal climatic fluctuations. Sediment concentrations in runoff and the runoff coefficient decreased exponentially with vegetation cover, while increases in steady infiltration rates were obtained with vegetation cover. Additional delays in runoff responses (longer time to runoff start and stabilization) and increases in the wetting front depth were observed with vegetation cover. Seasonal variations in soil surface state and moisture strongly influenced hydrological responses; although the influence of season on the analysed hydrological responses was attenuated by vegetation cover, especially in the case of infiltration rates. We also determined a practical ground cover threshold for site restoration and evaluation of over 50% vegetation cover, which could help achieve an optimum biological control of hydrological soil responses in the studied environment.     

Effects of soil management practices and tillage systems on surface soil water conservation and crust formation on a sandy loam in semi-arid Kenya

The effect of different soil management practices on crust strength and thickness, soil water conservation and crop performance was investigated on a ferric lixisol in a semi-arid environment of eastern Kenya.

The study proved that manure and mulching with minimum tillage have a greater effect on the water balance of crusted soils and maize emergence. There was increase in steady infiltration rates, amount of soil water stored in the soil and better drainage. The physical effect of mulch was less important in the rehabilitation of crusted soils in the study site when it was incorporated into the soil. Manure and surface mulch with minimum tillage should therefore be taken into account in land management and water conservation in the semi-arid areas of Kenya. The response of crops to the improved water availability due to manure with minimum and with conventional tillage and surface mulch was very clear. These management practices should be recommended when considering the effectiveness of soil and water management techniques in the study area.     

紫薯冰皮月饼的皮料工艺研究

[目的]研究以紫薯做为皮料加工制作冰皮月饼的最佳皮料工艺配方。[方法]对冰皮月饼的传统加工工艺进行改革,在皮料制作中加入紫薯,通过单因素与正交试验,确定以紫薯作皮料生产冰皮月饼的最佳工艺配方。[结果]试验表明,影响紫薯冰皮月饼皮料品质的主次因素依次为:牛奶添加量、澄面(小麦淀粉)添加量、紫薯泥添加量、糯米粉添加量、粘米粉添加量;皮料的最佳工艺配方为:糯米粉40 g、粘米粉40 g、澄面25 g、紫薯泥40 g、牛奶185 g、糖粉50 g、色拉油20 ml。[结论]此法制作的紫薯冰皮月饼皮料感官性状良好,颜色偏紫,新颖独特,具有一定的市场潜力。