ROTHAMSTED STUDIES OF SOIL STRUCTURE VI.

An ultrasonic method has been used to measure the stability index, σ, for each horizon of six soils. They provided three soil series comparisons: Hanslope-Ragdale, Evesham-Denchworth and Flint-Salop, in which the first-named series in each pair is ‘rarely problematic’, and the second ‘commonly problematic’ in management. The results for the top soils are presented in terms of the relationship between σ and the concentrations of those soil constituents likely to contribute to stability of aggregates: organic matter, clay, iron and aluminium oxides, and calcium carbonate. Regression analysis indicates significant correlations for all except the iron and aluminium oxide components. For each soil pair, the ultrasonic measures of stability did not reflect soil management experience, either for surface or sub-soil horizons. In general the commonly problematic soil appeared to have the same if not higher stability than its rarely problematic partner. Ultrasonic measurement of stability to dispersion, whilst indicating possible mechanisms of soil aggregate formation and breakdown, gives little help in identifying soil management potential.     

ROTHAMSTED STUDIES OF SOIL STRUCTURE IV.

Porosity and gas diffusion have been measured within dry crumbs sieved from the horizons of one soil from each of the Hanslope, Ragdale, Evesham, Denchworth, Flint and Salop series. Crumb porosities, ?c, ranged from 0.19 to 0.33, dimensionless gas diffusivities, D_c/D₀, from 0.015 to 0.098, and the effectiveness of unit pore space for diffusion, given by α_c= (D_c/D₀)/?_c, from 0.06 to 0.29. Values of ?_c and D_c/D₀ were used to calculate complexity factors k_c for the crumb pores. The results are discussed in terms of soil texture, pore size, ease of soil management, and the frequency and intensity of wetting and drying of the soil in each horizon. None of the results suggests why the soils of the Ragdale, Denchworth and Salop series should be more difficult to manage than the others.     

ROTHAMSTED STUDIES OF SOIL STRUCTURE VII.

Natural aggregates of topsoil samples of six British soils (Hanslope, Ragdale, Evesham, Denchworth, Flint and Salop) were incubated with added nutrients and changes in their stability to wet sieving determined. Under anaerobic incubation the type of nutrient added had little effect on stability. Aerobic incubation with glucose gave a larger proportion of stable aggregates than with water. With peptone stability usually decreased, and occasionally increased, which may indicate differences in the binding mechanisms of the soil particles. Both sterile and unsterile aggregates incubated with water became more stable than controls; the rapidity of this change suggested a physical, rather than microbiological cause. Very stable grassland aggregates changed little on aerobic incubation with water, but became more stable with solutions of glucose or peptone. Artificial aggregates made from the same soil developed considerable stability to water on aerobic incubation, but remained almost totally unstable when incubated anaerobically.     

ROTHAMSTED STUDIES OF SOIL STRUCTURE III

The response of three pairs of soils having contrasting management behaviour to changes in water content was investigated by measuring moisture characteristics, shrinkage, and pore size distributions by mercury porosimetry. Sample preparation for mercury porosimetry was by direct drying, or water replacement by methanol and liquid CO₂ followed by evaporation above the critical temperature. In heavy textured horizons, water release on shrinkage between -0.05 and -15 bar matric potentials occurs when pores of 10–200 nm equivalent plate separation contract. Structure development is dependent on the stability and regeneration of pores in the size range 200 nm-30 μm during cycles of wetting and drying. Soils with little stable porosity in this size range show nearly normal shrinkage and have coarse structural units, whereas soils with stable or regenerating porosity depart more from normal shrinkage and structure in the profile tends towards a finer per unit. The application of mercury porosimetry shows promise for determining possible porosity limitations in soil profiles.     

ROTHAMSTED STUDIES OF SOIL STRUCTURE 1.: PURPOSE OF THE PROJECT, SOILS SELECTED, AND GENERAL CONCLUSIONS

The agricultural background, morphology, and classification of soils from the Hans lope, Ragdale, Evesham, Denchworth, Flint and Salop series are presented together with basic analytical measurements of particle size and chemistry and with some details of the field water regimes. This information serves as essential background to other studies of soil structural properties as they relate to management of the same soils.     

ROTHAMSTED STUDIES OF SOIL STRUCTURE II. MEASUREMENT AND CHARACTERISATION OF MACROPOROSITY BY IMAGE ANALYSIS AND COMPARISON WITH DATA FROM WATER RETENTION MEASUREMENTS

Macroporosity (>60 μm) in the three pairs of soils described in Part I was measured and characterized by image analyses. There are significant differences in macroporosity between the soils in each pair, particularly in the subsoil horizons. The results show that the Ragdale, Denchworth and Salop soils are more impervious than those of the Hanslope, Evesham and Flint soils. Comparison of the image analysis results with those derived from air content at 0.05 bar suction shows that in most cases macroporosity by the former is larger. In image analysis the maximum diameter of each pore is measured whereas the water retention method measures the diameter of the smallest exit point of each pore. Differences between the two types of measurement will thus be at a maximum in soils containing many large pores with narrow exit necks.     

CHLORIDE LEACHING IN THE ROTHAMSTED DRAIN GAUGES: INFLUENCE OF RAINFALL PATTERN AND SOIL STRUCTURE

Calcium chloride giving 253 kgClha^?1 was applied to the 20-inch and 40-inch 1/1000 th acre drain gauges after drainage re-started in 1974. It was tagged with ³⁰Cl in the 40-inch gauge. After two preliminary peaks in each gauge, chloride concentration was related to cumulative drainage in the 20-inch gauge with an overall pattern of peak, decline and tail, interrupted by subsidiary peaks, whereas in the 40-inch gauge it declined very slowly with marked fluctuations. Total chloride and ³⁰Cl behaved similarly. A simple computer model simulated the main features of the relationship well for the 20-inch gauge, but less satisfactorily in the 40-inch gauge and only if water was assumed to move in a very small proportion of the clay in the lower half of the gauge. These simulations and some for model rainfall regimes suggested that the shapes of the relationships were greatly influenced by rainfall pattern and by retention of soil solution in fine pores during movement in larger pores. Possible effects of soil structure on leaching are discussed.     

高聚物土壤结构改良剂的研究Ⅰ.淀粉接枝共聚物改良赤红壤的研究

以天然或合成的聚合物作为土壤结构改良剂在近年来引起了人们的关注[1～3]，聚合物土壤结构改良剂通过其带功能基团的分子和分散土壤颗粒之间以缠绕、包裹、贯穿、吸附乃至形成化学键等方式创建和稳定水稳性团粒结构，在提高土壤物理肥力，改善土壤保肥性、保水性、改良盐碱土以及特别在抑制水土流失方面具有重要作用[4]。     

海绵田土壤结构特性与土壤肥力关系的研究

为了综合研究高产稳产田的肥力性状,自1971年以来,我们在山西省大寨大队及其邻近地区于玉米、小麦主要生育期内,测定了海绵田、非海绵田以及加快熟化新修地的土壤有机质、全量氮、磷、钾;并对微生物的季节性变化作了三年的测定;分别测定了雨季和旱季土壤水分和温度的变化;同时还利用薄片研究了土壤结构与土壤肥力的关系.     

土壤结构的性态研究

提高土壤肥力的目的主要在于充分发挥土壤潜在能力,保证农作物的高额稳产.为了达到这个目的,必须定向控制土壤的变化,改善土壤状况.土壤肥力是各种土壤性质的综合表现,并随着环境和时间而不断变化.要彻底了解土壤肥力,不仅要明悉土壤供应肥、水的容量和供应的快慢及持续时间,还要考虑肥、水的协调和植物根系的生活条件,这就是我们所称的肥力基础(简称肥基).     

INTERNAL STRUCTURE OF TILLED SOIL

Samples of tilled soil were impregnated with paraffin wax and were sectioned by sawing. The distribution of angles of incidence between voids and aggregates on the sections were investigated using random lines in three orientations. The angular distributions were found to be isotropic. Incidence angles near to normal were found to be more probable than in idealized beds of spherical aggregates. Distributions of aggregates and voids were examined along horizontal lines on the soil sections using an approach developed in communications theory. Soil structures in the size range from I to 5 mm were defined exactly by sets of sixteen transition probabilities. Differences were observed in the tilths produced by a mouldboard plough, a tine cultivator, and a rotary cultivator. The soil structures were different at different depths and changed with time after tillage. Transition probabilities measured in this way can be used in stochastic processes to simulate large tilths in a computer. The techniques described here could be adapted to the study of the distribution of soil structural features at any scale.     

STUDIES OF SOIL ORGANO-MINERAL FRACTIONS

Sand-, silt-, and clay-size organo-mineral fractions were isolated in bulk from surface horizons of five soils following ultrasonic dispersion in water. Good clay separation was achieved for all except one highly organic, calcareous clay soil. Organic-N and -C were concentrated in the clay and silt fractions but for each soil the organic C : N ratio decreased in the order sand > silt > whole soil > clay. Acid hydrolysis of the silt and clay fractions revealed a slight concentration of amino acid-N and NH₄-N in the clays but only small differences in the distribution of individual amino acids were observed. The results suggest that both silt and clay fractions may be important in the stabilization of soil organic matter.     

免耕法对土壤结构影响的研究

通过对江苏省５大农区５个点连续免耕两年后土壤容重收缩性能和破碎强度的测定,结果表明：免耕能改善土壤结构和土壤排水通气状况。体变率与土壤〈０．０１ｍｍ的物理性粘粒和〈０．００１ｍｍ粘粒含量相关密切;常耕与免耕破碎强度的差值也与粘粒含量有一定的相关。     

FIELD STUDIES OF THE SOIL ATMOSPHERE

A study was made of the concentrations of ethylene and oxygen in the soil atmosphere under field conditions at three contrasting sites. The duration of the experiments ranged from 6 weeks to 9 months. A clear relationship between high moisture content and both the production of ethylene and the depression of oxygen levels was found in a sandy loam, although there was great variability between replicate sampling points. Concentrations of oxygen in a heavy clay soil remained below 10 per cent (v/v) throughout the winter and spring, followed by a gradual rise to near-atmospheric levels. Concentrations of ethylene were not correlated with those of oxygen, except in the winter, but rose logarithmically with soil temperature during the spring, increasing by twenty times over the range 4-1 I °C. There was no significant difference between plots which had been subjected to different drainage treatments, and again there was great variability from point to point. In a more permeable clay soil, however, the levels of oxygen were higher, and were related to the proximity to drains and the height of the water table, but not to the levels of ethylene. The concentration of ethylene showed a similar logarithmic increase with temperature to that observed in the heavy clay, and exceeded I ppm throughout the period May-July. The factors which have the greatest influence on the concentrations of ethylene in the soil were considered to be temperature, depression of oxygen concentration, the availability of substrates for microbial activity and the effect of soil moisture content on the air-filled porosity of the soil. Concentrations of ethylene greatly in excess of those which, under some circumstances, inhibit root growth, are likely to be of widespread occurrence in heavy soils during the spring and early summer and in light soils when unusually wet.     

土壤环境变化对土壤动物群落影响的研究

土壤是环境系统中物质与能量交换的枢纽 ,土壤动物在土壤物质能量迁移转化过程中具有特殊的功能和作用。然而 ,随着人类活动对环境影响的加剧 ,原生植被受到破坏 ,各种污染物质不断在土壤中富集 ,对土壤动物的生存繁衍带来严重威胁 ,目前土壤动物学者的研究 ,主要集中在土壤动物在成长过程中的作用 ,理化性质的改良 ,土壤养分循环以及区系分类等 ,很少涉及土壤动物与环境特别是污染环境关系的研究。农药是目前主要的化学性环境污染物 ,农药污染对自然和农田生态系统的结构和功能都有影响[1] ,有实验表明 ,农药污染对土壤动物新陈代谢及卵的…     

核素示踪技术在土壤侵蚀研究中的应用进展

介绍了单核素 (137Cs、2 10 Pb和7Be)、复合核素 (7Be、2 10 Pb、2 2 6 Ra和137Cs)及稳定性稀土元素 (REE)示踪技术在土壤侵蚀速率、泥沙沉积速率、侵蚀产沙时空分布和侵蚀类型转变等研究中的应用现状 ,并对各方法做了简要评价。