THE MEASUREMENT OF SOIL-WATER HYSTERETIC RELATIONSHIPS ON A SOIL MONOLITH

Soil water properties of an undisturbed uniform soil monolith were studied under laboratory conditions. Water content, hydraulic conductivity and soil water suction were measured simultaneously on a full cycle starting from saturation, drying to a small water content and then wetting until saturation was reached again. The results showed clearly the hysteretic nature of the relations between water content and suction and between hydraulic conductivity and suction, but not between hydraulic conductivity and water content.     

A SIMPLE AND RELIABLE TENSION TABLE

A tension table may be constructed from a Perspex tray ? in. thick, approximately 12 in. wide and 19 in. long with 21 drainage channels. With a filter paper membrane, which gives rapid transmission of water and can be readily changed when contaminated it may be used to equilibrate 3–4 kg of moist soil overnight at suctions up to 100 cm of water. Several small samples may be handled at once by using small filter-paper trays.     

A SIMPLE AVAILABLE SOIL NITROGEN INDEX

Available soil-N values in commonly cultivated East African soils were determined in the laboratory by several methods, and correlated with one another. Mineralizable-N was correlated more with total-N than with organic-C. The values of mineralizable-N (Δ mineral-N) obtained on aerobic incubation were correlated with crop yield and nitrogen uptake in greenhouse experiments. The yield of dry matter and N uptake by the tomato crop in the absence of applied nitrogen were significantly correlated with Δ mineral-N in the soils; the degree of correlation decreased with increasing rates of fertilizer-N applied and Δ mineral-N and dry-matter yield were not correlated at the largest rate used. N uptake by the crop was significantly correlated with Δ mineral-N at all rates of applied nitrogen. The Δ mineral-N value determined on soil samples conditioned by 6 weeks incubation followed by 3 weeks air drying was considered to provide a good index to available nitrogen.     

A SIMPLE AND RAPID METHOD OF SOIL WATER DETERMINATION

A wide-mouthed pycnometer was employed for rapid determination of soil water. The principle involved is to weigh the pycnometer when filled with the soil sample and water. The particle density of soil needs to be known. There is no necessity to add exact volumes of water. For the 7 soils studied, the water content values obtained by the proposed method were similar to those by oven-drying.     

A SIMPLE COMPUTER MODEL FOR LEACHING IN STRUCTURED SOILS

A layer model for the movement of solutes in soil has been developed in which, as a working approximation, the soil solution is partitioned into mobile and retained phases. Only the mobile solution is displaced during water movement, and equilibrium is assumed to be established between the mobile and retained phases when flow ceases, giving holdback of solute. The model permits the displacement of the mobile solution through an indefinite number of layers when large amounts of rain fall. It can be assumed either that water and solute are stored in the bottom layer and can be withdrawn up the profile by evaporation or that they drain from the bottom layer. Predicted soil nitrate concentrations agreed reasonably well with those measured in a field experiment and indicated some sensitivity to layer thickness. The capacity of the model to predict concentrations in drainage is demonstrated.     

A SIMPLE ELECTROLYTIC RESPIROMETER-LEACHING TUBE COMBINATION FOR SOIL METABOLISM STUDIES

An apparatus is described consisting of a combination of an electrolytic respirometer and a leaching tube. This allows determination in the same soil sample of O₂ uptake, CO₂ release, and N release as NO₃^?, NH₄⁺, and NH₃ Release of other water soluble components can also be followed. Unlike other electrolytic respirometers the apparatus measures O₂ uptake directly, the O₂ being replaced periodically by electrolysis. Fluctuations in electrolyte level due to changes in atmospheric temperature and pressure are compensated for using a control apparatus with a volume equal to the air space in the experimental apparatus. The simplicity of the apparatus allows ready replication.     

LIMESTONE PARTICLE SIZE AND RESIDUAL LIME CONCENTRATION AFFECT PH BUFFERING IN CONTAINER SUBSTRATES

The objective was to quantify how the concentration and particle size of unreacted “residual” limestone affected pH buffering capacity for ten commercial and nine research container substrates that varied in residual calcium carbonate equivalents (CCE) from 0.3 to 4.9 g CCE·L^?1. The nine research substrates contained 70% peat:30% perlite (by volume) with dolomitic hydrated lime at 2.1 g·L^?1, followed by incorporation of one of four particle size fractions [850 to 2000 μm (10 to 20 US mesh), 250 to 850 μm (20 to 60 US mesh), 150 to 250 μm (60 to 100 US mesh), or 75 to 150 μm (100 to 200 US mesh)] of a dolomitic carbonate limestone at 0, 1.5 or 3.0 g·L^?1. Substrate-pH buffering was quantified by measuring the pH change following either (a) mineral acid drenches without plants, or (b) a greenhouse experiment where an ammonium-based (acidic) or nitrate-based (basic) fertilizer was applied to Impatiens wallerana Hook. F. Increasing residual CCE in commercial substrates was correlated with greater pH buffering following either the hydrochloric acid (HCl) drench or impatiens growth with an ammonium-based fertilizer. Research substrates with high applied lime rate (3.0 kg·m^?3) had greater pH buffering than at 0 or 1.5 g·L^?1. At 3 g·L^?1, the intermediate limestone particle size fractions of 250 to 850 μm and 150 to 250 (20 to 60 or 60 to 100 US mesh) provided the greatest pH-buffering with impatiens. Particle fractions finer than 150 μm reacted quickly over time, whereas buffering by particles coarser than 850 μm was limited because of the excessively slow reaction rate during the experimental periods. Addition of acid from either an ammonium-based fertilizer or HCl reduced residual CCE over time. Dosage with 40 meq acid from HCl per liter of substrate or titration with HCl acid to substrate-pH of 4.5 were well-correlated with pH buffering in the greenhouse trials and may be useful laboratory protocols to compare pH buffering of substrates. With nitrate fertilizer application, residual CCE did not affect buffering against increasing pH. Residual limestone is an important substrate property that should be considered for pH management in greenhouse crop production under acidic conditions.     

一种简单的土壤热惯量野外实测方法

本文采用一种野外实地测量土壤热扩散率结合室内测定该土壤热容量的方法,计算实际情况下土壤热惯量与水分含量间的关系。文中对该测量方法进行了推导。并将之应用于黄淮海地区不同土壤类型,在给出了不同土壤类型和质地的热惯量值的同时,对该方法的重复性,稳定性,准确性进行了检验。     

A SIMPLE AND INEXPENSIVE APPARATUS FOR AUTOMATICALLY CONTROLLING SOLUTION FLOW RATES THROUGH SOIL COLUMNS

Accurate control of rate of flow of solution through soil columns is important in laboratory studies of leaching, but is difficult to achieve because of fluctuations in permeability. A simple and inexpensive method of automatically maintaining a constant flow-rate through several columns simultaneously is described. The apparatus comprises (i) a rotating delivery system which distributes the leaching solution equally to eight compartments, (ii) a system for automatically regulating the flow through each column to keep pace with the solution delivered, and (iii) an automatic fraction-collector to collect the effluent from the columns. Using this apparatus the standard deviation of the volumes delivered to the eight individual columns was less than 2 per cent of the mean, provided the flow rate was faster than 10 ml/h.     

FATE AND TRANSPORT OF CONTAMINANT LEAD IN SPODOSOLS: A SIMPLE BOX MODEL ANALYSIS

A dynamic simulation based on a simple box model was made to predict Pb transport in spodosols of the Hubbard Brook Experimental Forest. Simulated results suggest that labile Pb in the forest floor may be undergoing a rapid loss, and that Pb content may reach an equilibrium within ～100 years with a steady-state level of approximately 0.2 kg ha^-1 (concentration = 1.3 μg g^-1). The predicted Pb loss from the forest floor is much higher than the observed Pb export based on zero-tension lysimeters, which are designed to optimize measurement of dissolved substances. It is suspected that lysimeters might have failed to effectively collect particles and colloids. The dissolved Pb²⁺ loss from the forest floor, which is governed by nonlinear retardation, is insignificant relative to total Pb losses, so linear rate removal of particles and colloids from the forest floor is an adequate approximation of Pb transport. The mineral soil is currently acting as a net sink for the Pb released from the forest floor. The model suggests that Pb content in and Pb output from the mineral soil has been increasing since the 1970s. This increase should continue until a steady-state is reached in about 100 years. Unlike the forest floor, the mineral soil loses its Pb via dissolved forms that are regulated by nonlinear adsorption/desorption retardation.     

A SIMPLE MATHEMATICAL MODEL FOR DIAGNOSIS OF NUTRIENT CONTENT AND DRY MATTER PRODUCTION IN WHEAT

The equation y = a + bx ^α + cx ^2α proposed as a general function of nutrition to describe the relationship between the concentration of nutrients in a plant and the production of dry matter. The function has a maximum if b>0? and ?c≤0, which corresponds to the optimal nutritional value; depending on the value of the parameter α it may have a point of inflexion which can occur before or after the maximum and at varying distances from it. The parameter a can be set to zero if necessary in which case the function passes through the origin. Hence its parametric form is flexible and suitable for describing the incidence of nutrients in dry matter production. Furthermore, it is very simple and easy to use. Its use in describing leaves of field-grown wheat at different stages of growth seems to indicate that it has some applicability compared with other commonly used functions, and given its flexibility it can offer advances in the understanding of mineral nutrition in plants. Although further assays are necessary, so that the physiological stage of the plant sample can be accurately defined, it seems that the value of α may define the physiological state of the plant, the particular circumstances of cultivation defining the parameters b and c. Thus, for example, in 1987, in experimental trials of wheat close to flowering, the value of α for nitrogen in the flag leaf was 1.75, for the second leaf 1.25, and 1.00 for the third. The corresponding stages of growth, although not very precisely defined, were close to the maximum for the first leaf, slightly declining in the second, but more so for the third. Post-anthesis, nitrogen in the first leaf had an α-value of 0.75; its physiological state now corresponding to a sharp decline in foliar weight. Other situations would give characteristic values of α, whose calibration over several carefully conducted trials would be used in plant nutrition diagnosis.     

简易节能猪舍的探讨

我们于1985年8月至1986年2月,在我校试验站进行了卷帘式、有窗式和无窗式(不装空调)三种猪舍的对比试验和观测,结果表明: 1.正北京地区,用上述三种猪舍饲养30～90kg的猪,各舍试猪日增重和饲料利用率,在夏秋冬三季均无显著差异; 2.卷帘舍夏季通风好,有利于防暑,但冬季保温较差;无窗舍夏季通风差,较闷热,冬季保温虽好,但湿度较大;有窗舍夏季防暑和冬季保温均较好; 3.无窗舍除大跨度空调猪舍外,小跨度自然通风光照猪舍不易采用;卷帘舍在北京及其以南地区可用于小跨度育肥及成年猪舍;有窗舍可用于饲养各种猪的小跨度猪含,各地均可采用。     

推求土壤水分运动参数的简单入渗法Ⅰ.理论分析

预报非饱和土壤水分运动必须首先获得土壤水分运动参数。土壤水分运动参数包括土壤水分特征曲线和导水率。本文使用积分方法求解了一维水平非饱和土壤水分运动问题,根据其建立了椎求非饱和土壤水分运动参数的简单人渗法,用以推求ｖａｎ Ｇｅｎｕｃｈｔｅｎ特征曲线模型中的参数α和ｎ。α和ｎ是根据湿润区的特征长度、吸渗率和土壤的饱和导水率（ｋ）来确定的,而非饱和导水率可由α、ｎ和ｋｓ确定。这一项的简单人渗法是基于Ｒｉ     

NURSERY RESPONSE OF ACACIA KOA SEEDLINGS TO CONTAINER SIZE,IRRIGATION METHOD,AND FERTILIZATION RATE

Planting koa (Acacia koa A. Gray) in Hawai‘i, USA aids in restoration of disturbed sites essential to conservation of endemic species. Survival and growth of planted seedlings under vegetative competition typically increases with initial plant size. Increasing container size and fertilizer rate may produce larger seedlings, but high fertilization can lead to surface and groundwater pollution and relatively low fertilizer use efficiency. Subirrigation systems may help mitigate this problem. Our study objective was to evaluate koa seedling growth with overhead or subirrigation over a range of container volumes (50 to 656 mL) and fertilizer rates (0 to 9.6 kg·m^?3). Increasing container volume from 50 to 656 mL yielded koa seedlings with 200% more height and stem diameter growth. Subirrigation resulted in less nutrient leaching losses and yielded seedlings of similar vigor as overhead irrigated seedlings. Subirrigation helps optimize fertilizer delivery, which may improve fertilizer use efficiency and reduce environmental contamination.     

CHARACTERIZATION OF WATER DISPLACEMENT IN SOILS USING SIMPLE CHROMATOGRAPHIC THEORY

Simple chromatographic equations were adapted to describe frontal water displacement by tracer-containing water in soils where only partial displacement occurs. The equations were shown to give excellent agreement with experimental data in five field experiments where tracer was added in artificial rainfall. The consequences of partial displacement for soil water replenishment in the root zone, salt leaching and ground water recharge are discussed.     

A SIMPLE MODEL FOR PREDICTING THE EFFECTS OF WINTER LEACHING OF RESIDUAL NITRATE ON THE NITROGEN FERTILIZER NEED OF SPRING CROPS

A model is described for predicting the amounts of nitrate residues remaining in the soil in the autumn and the extent to which these are lost by leaching during the winter. It is used to predict the effects of winter rainfall on the growth of spring crops. The model is based on the assumption that any nitrate which remains in the effective rooting zone of the spring crop after the winter will be equally available and any nitrate leached below it will be totally unavailable. The losses of nitrate were estimated from the excess rainfall and the water holding capacity of the soil. The model was tested against the results of published N response experiments in the Netherlands and the UK. It predicted the differential effects of winter rainfall with reasonable accuracy, but tended to overestimate the spring nitrate contents observed in the Dutch experiments and underestimate those for the English data. These deviations appeared to be associated with errors in the estimation of the amounts of nitrate remaining in the soil in the autumn. With certain reservations, the model would appear to provide helpful advice for adjusting spring fertilizer dressings for the effects of differences in winter rainfall.     

土壤溶质运移CDE模型参数估计的一种新方法——截距法

为了满足日益增长的人口对粮食的需求 ,农用化学物质被广泛应用 ,这些物质可通过各种途径进入土壤 ,因此研究土壤中农用化学物质的运移、转化对于防止水环境污染、促进农用化学物质的高效、发展可持续农业有着重要的意义[1 ] 。对流—弥散方程 (ＣＤＥ)是研究土壤溶质运移的一种经典模型 ,参数的估计是应用ＣＤＥ方程的一个关键问题。传统估计ＣＤＥ方程参数的方法有统计方法和确定性方法两种。统计方法主要包括最小二乘法、最大似然法和矩分析法[2～ 5] ,但由于未知因素太多及初值的选择不当 ,采用统计方法所得参数不唯一[6] ;同时 ,仅靠曲…     

A SIMPLE MODEL FOR PREDICTING THE EFFECTS OF LEACHING OF FERTILIZER NITRATE DURING THE GROWING SEASON ON THE NITROGEN FERTILIZER NEED OF CROPS

The model is based on the concept that there is an effective rooting depth above which all the inorganic N in the soil is equally available and below which all N is totally unavailable. The extent to which nitrate is leached below this depth is calculated from the excess rainfall over evapotranspiration and the water holding capacity of the soil. The model was tested against the results of N fertilizer experiments with lettuce, French beans and overwintered onions which had been carried out in at least 2 years (and often more) on adjacent sites of the same field. The yields from all of the experiments with each crop were plotted against the level of fertilizer applied and against the difference between that applied and that lost by leaching. Comparison of these graphs showed that correcting for leaching in this way greatly reduced the variability between the response curves. The model was also tested against the results of similar experiments with Brussels sprouts grown on different sites with different combinations of base and top dressing. The results showed that the poor response to top dressing could be explained by the relatively small amounts of N in the base dressing which were leached from the rooting zone of this crop. It appears that the model will enable worthwhile adjustments in N fertilizer dressings to be made for differences in rainfall, provided that leaching occurs during the early stages of crop growth when uptake is small.     

COHESION OF SOIL PARTICLES AND THE INTRINSIC RESISTANCE OF SIMPLE SOIL SYSTEMS TO WIND EROSION

In a simple dry soil system in which erosion is taking place by virtue of the impact of saltating sand grains, the intrinsic variables affecting soil resistance can be investigated with the aid of a mathematical model. The soil erodibility depends on the cohesiveness of the soil which is indicated by the tensile strength. This is directly proportional to the packing density of the system, to the co-ordination number of the particles, and to the inter-particle bond strength. Tensile strength is inversely proportional to the cube of the particle diameter. In a cohesive material any decrease in the particle size produces a great increase in the tensile strength and hence the mechanical stability is improved, but because the particles are lighter they are easily eroded once they are disturbed.