SULPHATE DISTRIBUTION IN SOLONETZIC SOIL WITH A WATER TABLE

Soil columns were used to study sulphate distribution in Thin Duagh Loam soil as influenced by the presence of a water table. The concentration pattern showed that retention was greater in the surface soil than at lower depths. The data suggest that sulphate tends to move more slowly than water in soil.     

绿肥压青后水稻生育期间土壤中还原性物质的动态变化

绿肥压青后随郎栽换或未经庸妙就栽秧,常会引起水稻黑根枯苗的“烧秧”现象。一般认为,还原性物质的毒害是引起这一现象的原因之一。然而引起毒害的还原性物质,主要是低铁还是硫化氢或其它还原性物质?则一直不大清楚。近年来不少研究者指出,水和土的氧化还原状况对水稻的生长发育和土壤养分状况有很大影响^[1-4],有的研究者指出,对于水稻土的氧化还原体系,应从其彼此相关而又不同的张度因素与数量因素两方面进行研究^[5-4],并提出了相应的研究方法^[6,7]。按照这些方法,1962年我们在研究绿肥压青后水稻生育期间土壤中还原性物质的动态变化时初步看出^[8]:活性有机还原物质在还原性物质总量的变化中起着主要的作用。在此墓础上又于1963年进行了田间小区试验,以探索绿肥压青后土壤中还原性物质舍量的变化及其对水稻生长的影响。现将所得结果整理如下。     

A MATHEMATICAL MODEL FOR THE DIFFERENTIAL MOVEMENT OF TWO SOIL CONSTITUENTS INTO ILLUVIAL HORIZONS: APPLICATION TO CLAY RATIOS IN ARGILLIC HORIZONS

The effects of the migration of two soil constituents into illuvial horizons is described by a set of equations. Differential movement of clay fractions during illuviation causes changes in the fine to total clay ratios in A and B horizons. A mathematical model is used for the interpretation of clay fraction data in order to estimate the degree of profile development, the amounts of fine and total clay which have moved, and to determine the original composition of the parent material. No bulk density data of the soil horizons are necessary for the computation. The equations can be programmed on desk calculators. Comparison with measurements on Alfisols in temperate regions was found to be satisfactory.     

土壤中离子扩散的动力学研究

本文首先从理论上分析了土壤中离子扩散的动力学问题，提出了土壤中离子扩散的三种动力学类型，即扩散的一级动力学、零级动力学和负一极动力学，并且还指出，一级动力学是土壤中离子扩散的普遍形式，负一级动力学只出现在过程的初期阶段，而扩散的零级动力学则存在于有快速表面反应的情况下。在此基础上进行了Ｍｇ＾２＋在土壤和石英砂中的扩散动力学实验研究，结果发现不论在２９８Ｋ还是在３０８Ｋ的温度下，两个体系中Ｍｇ＾２＋     

KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER

The rate of ion exchange reactions of humic substances (humic acid and peat) with lead ions was investigated at 25 °C. All experiments were carried out under finite solution-volume conditions. To the well-stirred aqueous suspensions of the above samples lead ions were added in such small amounts that, after attainment of the equilibrium, the initial equivalent fraction of lead in the humic substance had increased only by a small amount. The kinetics of such differentially small ion exchange processes were studied as a function of the initial lead content of the samples. The experiments showed that the absolute rates for the uptake of small amounts of lead ions decrease, if the initial lead content of the samples increase. The relative rates of ion exchange, i.e. the rates with respect to the extent of each reaction, showed a more complicated behaviour, as they can exhibit a minimum at a certain initial lead content of the sample. The rate-determining step of the above ion exchange experiments was shown, by interruption tests, to be diffusion of the ions through the Nernst-film surrounding the ion exchanger particles. Theoretical calculations of the rates of film-diffusion controlled ion exchange processes were carried out and the results revealed that the rates of any differential ion exchange reaction should decrease with increasing initial content of the ion adsorbed, their exact magnitude depending, among other quantities, strongly on the separation factor. The relative rates for the attainment of the equilibrium, on the other hand, depend much less on the initial ionic composition of the ion exchanger. A comparison of the experimental and the calculated results yields satisfactory agreement if the experimentally determined dependence of the separation factor on the lead content of the samples is taken into account.     

KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER

The rate of ion exchange of humic substances (humic acid and peat in the hydrogen form) with lead ions was investigated. As in processes occurring in nature, the lead solution was added in all our experiments slowly and continuously at a constant feed rate to the well-stirred water-suspended humic substances. Control experiments were also performed with a well-defined synthetic ion- exchange resin (carboxylic acid type). The uptake of divalent lead ions by the humic substance and by the ion-exchange resin, which is coupled with the release of an equivalent amount of hydrogen ions, proceeds as a function of time according to a characteristic sigmoidal curve. During the initial phase, the rate of ion exchange increases continuously with time, even though the humic substances become more saturated with lead ions. Theoretical calculations, based on a film diffusion process as the rate-determining step, show that this behaviour should indeed be observed if any solution, containing exchangeable counter ions, is added continuously to an ion exchanger suspended in a solvent. The theory predicts further, in agreement with the experimental results, that in the initial phase of the ion-exchange reaction, the uptake of the counter ions is proportional to the square of the time. If experiments are performed with different rates of addition of the counter ions, the time required to exchange a certain amount of counter ions should be proportional to α^-1/2, where α is the rate at which the ions are added. This prediction is also in accordance with the experimental results.     

A BASIS FOR THE CLASSIFICATION OF SOIL

Considering the nature of soil and the ends which a classification must serve, principles are stated whereby a soil classification may be devised for application over extensive areas of varied soil composition. Naturally occurring bodies of soil, each with a high degree of homogeneity, are apparent rather than real individuals as their properties overlap to form a continuum. This continuum is multi-dimensional because soil is characterized by numerous properties. The procedure of devising a classification is one of subdividing the continuum such that class boundaries accommodate, as far as possible, apparent individuals rather than of grouping like apparent individuals together. A classification may be used to locate the position of a profile in the continuum and so define its relationship with other profiles. It may also be used to indicate the soil composition of land by using soil classes on a map to show differences in the soil mantle. The latter procedure may best be regarded as land classification or soil mapping rather than soil classification; a class of land or mapped area seldom contains profiles belonging exclusively to a single class, whereas a soil class never contains profiles of another class. The soil form, a specific arrangement of diagnostic horizons, is introduced as a category above the series to facilitate the identification of soil profiles. Member series of a form are defined according to property variations within the diagnostic horizons of the form. It is suggested that a binomial system of profile nomenclature, using the form and the series, would have much to commend it.     

THE MEASUREMENT AND MECHANISM OF ION DIFFUSION IN SOIL

If an exchangeable ion in soil diffuses along a liquid and solid pathway, its diffusion coefficient may be expressed as where D, v, f, C are diffusion coefficient, volume fraction, impedance factor, and concentration terms and the suffixes _l,_S refer to liquid and solid. The self-diffusion coefficient of the ion is then where D′, D′_t, and D′_s, are self-diffusion coefficients. D and D′ will vary with concentration. In diffusion out of the soil to a zero sink, the appropriate average diffusion coefficient is, approximately, the self-diffusion coefficient in the undisturbed soil. Diffusion of one ion species is influenced by other ions diffusing in the system through the diffusion potential set up. When ions are diffusing to plant roots, the diffusion potential is likely to be small. A more likely, though more complicated, expression for D than the first equation above is derived by assuming the ion to follow solid and liquid pathways in series as well as in parallel.     

A NEW TECHNIQUE FOR SOIL PIT ILLUSTRATIONS

The difficulty of illustrating soil pit detail can be overcome by using selected grey density slices of original photographs. The technique of density slicing for illustrations involves the separate printing of a particular shade of grey from the original, which picks out the detail required.     

A COMPARISON OF POTASSIUM-ACTIVITY RATIOS DERIVED FROM EQUILIBRATION PROCEDURES AND FROM MEASUREMENTS ON DISPLACED SOIL SOLUTION

Direct and indirect methods of determining cation ratios of natural soil solutions are reviewed. The problems of comparing their results are discussed. K activity ratios derived from measurements on ethyl alcohol-displaced soil solutions and values determined for the same soils by the Q/I equilibration procedure were in excellent agreement. An approximate rapid Q/I procedure using two K-Ca solutions whilst less precise in its determination of activity ratio would be useful for routine purposes. The use of a proportionality constant to calculate activity ratios is acceptable.     

DEVELOPMENT OF A SOIL N TEST FOR FERTILIZER REQUIREMENTS FOR WHEAT

Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO^? ₃)- N, soil ammonium (NH ⁺ ₄)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO^? ₃-N and NH ⁺ ₄-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH ⁺ ₄-N and NO^? ₃ -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO^? ₃-N.     

A NEW HAND-HELD RECORDING PENETROMETER FOR SOIL STUDIES

This paper describes and evaluates a new solid-state recording hand-held cone penetrometer developed for in-situ soil studies. Force is measured by a strain-gauged transducer, and depth by an accurate optical system. Data for up to 20 penetrations per plot are stored and processed within the instrument in the field. The new penetrometer has been evaluated in field and soil tank experiments in comparison with three widely contrasting existing penetrometers ranging from a simple hand-held penetrometer to a trailer-mounted power-driven instrument. The results indicated that the simple hand-held penetrometer gave appreciably different cone resistance profiles from the other instruments. In particular, spurious ‘treatment effects’ obtained from the tillage experiment were shown to be due to inadequate instrument performance. The new solid-state recording hand-held penetrometer gave results comparable with those obtained from the more complex trailer-mounted instrument and another hand-held recording penetrometer.     

利用钼值作为冬小麦缺钼土壤诊断指标的探讨

连续2年的盆栽试验结果说明,冬小麦产量随土壤有效钼含量或钼值提高而增加,当钼值大于8.0时,冬小麦籽粒产量大于最高产量的90％,冬小麦施钼增产不显著;结合多年以各地土壤进行的盆栽、田间试验结果说明,冬小麦施钼增产效果与土壤有效钼含量相关性不大,但冬小麦施钼增产率随土壤钼值提高而下降,钼值作为冬小麦土壤钼有效性指标能适用于不同土壤条件,拟定钼值8.0～8.5是冬小麦施钼的临界值。     

POTASSIUM RESERVES IN A SANDY CLAY SOIL FROM THE SAXMUNDHAM EXPERIMENT: KINETICS AND EQUILIBRIUM THERMODYNAMICS

Potassium-calcium exchange equilibria in, and the kinetics of K release from, soil from the Nil and PK treatments of the Saxmundham Experiment, Rotation 1, and the Ga, Ca + K and K saturated panicle size fractions of the soils were investigated. The free energy and enthalpy ot exchange showed K preference in all the solids. Selectivity for K decreased with increasing particle size and pre-treatment with K salts. A comparison of the ‘differential enthalpy of exchange: per cent K saturation’ relationship for the whole soil with those of the particle size fractions suggests that soil dispersion during particle size separation also decreased K selectivity significantly. When related to the mineralogical composition of the soil, the differential enthalpy data suggest that maximum K. selectivity is associated with a vermiculite/smectite component of inter-stratified minerals in the soil. Isotopic exchange using ^4sCa on the decalcified solids showed a measurable rate of exchange for the Ca forms of the <0.2 and 0.2–2 /μm fractions. This is attributed to traces of blocking materials (CaCO₃ or hydroxy-aluminium polymers), which are removed or rendered porous during treatment with dilute KCl solution, so that isotopic exchange with Ca is then much more rapid. The kinetics of K extraction with a Ca saturated resin, interpreted on the basis of a three-compartment model, suggest that sorbed K and K released by ‘fast’ and slow processes, representing sites of low and high K selectivity, were associated with minera-logically distinct phases in the various particle size fractions.     

RECONNAISSANCE FOR SOIL SURVEY

The total length of soil boundary on a map can be measured by counting the number of intercepts between boundaries and a randomly distributed array of sampling lines. It is thus also possible to estimate the length of the same boundaries before survey by means of a similar array of field traverses. The per cent sampling error of estimates of boundary density (boundary per unit area), is approximately the reciprocal of the square root of the number of intercepts.     

黑土农田养分平衡与养分消长规律

通过 1 1年的定位试验结果表明 ,典型黑土农田 1 1年不施N肥 ,N素的自然供给力由 92 %下降到 5 0 %～ 60 % ;不施P肥 ,P素的自然供给力由 98%下降到 80 %～ 90 % ;不施钾肥 ,K素的自然供给力也由 1 0 0 %缓慢下降接近 90 %。农田养分平衡盈亏及其变化决定了土壤养分消长规律 ,其中有效磷的消长与P素盈亏的相关模型为Y =2 895 0 1 3 4x ,速效钾的消长与K素盈亏的相关模型为Y =1 8 81 0 1 63x。