Call number: LD2668 .T4 1986 D56 / Master of Science / Agronomy

Thesis (MScAgric)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: The Eksteen method of lime requirement determination, based on the ratio of Ca+Mg:H (R-value), is widely used in the Western Cape and has proven to be extremely accurate for most soils. However, the Eksteen method is known to give erroneous predictions of lime requirement for certain soil groups. These include sandy soils (notably pale coloured sandy soils), organic-rich topsoils and strongly structured, Mg-rich subsoils. The objective of this study was to examine the nature of the Eksteen RpH relationship for these problem soils, and to develop appropriate modifications to the Eksteen method, where possible. A population of both normal and problem soils was selected and analysed, the RpH relationships of the soils were determined, and various relationships were examined. The principal findings with regard to the nature of the Eksteen RpH relationship were as follows: 1. The lime requirements of pale coloured sandy soils can be most accurately determined on an equivalent basis relative to the total extractable acidity, after the total extractable acidity has been corrected for residual lime. 2. The previously observed and acknowledged inaccuracy of the Eksteen method on organic-rich soils stems from the pH-dependant acidity component of the organic matter. The accuracy with which the lime requirement of these soils is predicted by the Eksteen method can be greatly improved by the application of an organic matter correction factor (OMCF) to the total extractable acidity, which is the parameter on which the lime requirement is then based. 3. In structured, Mg-rich subsoils the pH-neutralising capacity of Mg is considerably lower than that of Ca, a factor which is not taken into account by the Eksteen method. The Eksteen method can nevertheless be corrected to overcome this discrepancy. The high levels of Mg in the structured, Mg-rich subsoils cannot be attributed to minerals in these subsoils containing brucite interlayers. 4. Toxic levels of AI may only be expected at soil pH values below approximately 4.7 as determined in 1M KC!. Soil organic matter and CEC have marked affects on AI extractability. In accordance with the objective that appropriate modifications to the Eksteen method should be developed if possible, theoretically-based correction factors were developed which will permit the use of the Eksteen method to be confidently extended to those soil groups (pale coloured sandy soils, organicrich topsoils and strongly structured, Mg-rich subsoils) for which it was formerly considered unreliable. / AFRIKAANSE OPSOMMING: Die Eksteen metode van kalkbehoeftebepaling, gebaseer op die verhouding van Ca+Mg:H (R-waarde), word oor die algemeen wyd in die Wes-Kaap gebruik en is baie akkuraat vir meeste gronde bewys. Dit is egter bekend dat die Eksteen metode verkeerde kalkbehoeftes vir sekere grondgroepe voorspel. Hierdie sluit sanderige grande (veral lig gekleurde sandgronde), organiesryke bogrande en sterk gestruktuurde, Mg-ryke ondergronde in. Die doel van hierdie studie was om die aard van die Eksteen R:pH verwantskap vir hierdie probleemgronde te bepaal, waar moontlik. 'n Populasie van beide normaal en probleemgrande is geselekteer en geanaliseer, die R:pH verwantskap van die grande is bepaal en verskeie verwantskappe is ondersoek. Die hoof bevindinge ten opsigte van die aard van die Eksteen R:pH verwantskap was as volg: 1. Die kalkbehoefte van lig gekleurde sandgronde kan akkuraat bepaal word op 'n ekwivalente basis, relatief tot die totale ekstraheerbare suurheid, nadat die totale ekstraheerbare suurheid gekorrigeer is vir residuele kalk. 2. Die voorheen bekende onakkuraatheid van die Eksteen metode op organiesryke gronde het sy oorsprong by die pH-afhanklike suurheid komponent van organiese material. Die akkuraatheid waarmee die kalkbehoefte van hierdie grande met behulp van die Eksteen metode voorspel kan word, kan noemenswaardig verbeter word deur die totale ekstraheerbare suurheid te korrigeer met behulp van 'n organiese materiaal korreksie faktor (OMKF). Die aangepaste totale ekstraheerbare suurheid is dan die parameter waarap die kallkbehoefte gebaseer word. 3. In gestruktuurde, Mg-ryke ondergrande is die pH-neutraliseringsvermoe van Mg aansienlik laer as die van Ca, 'n faktor wat seide in berekening gebring word by die Eksteen metode. Die Eksteen metode kan tog gekorrigeer word om hierdie tekortkoming te oorkom. Die hoe vlakke van Mg in gestruktuurde, Mg-ryke ondergrande kan nie aan die teenwoordigheid van minerale in die ondergrond, wat brusiet tussenlae bevat, toegeskryf word nie. 4. Toksiese AI vlakke sal alleenlik by grond pH waardes laer as ongeveer 4.7, soos bepaal in 1M KCI, verwag word. Grand organiese materiaal en KUK het 'n noemenswaardige effek op ekstraheerbare AI. In ooreenstemming met die doelwitte om toepaslike wysigings aan die Eksteen metode aan te bring, is teoreties gebaseerde korreksiefaktore ontwikkel, wat die gebruik van die Eksteen metode verder verbreed om daardie grondgraepe (lig gekleurde sanderige grande, organies-ryke bogrande en sterk gestruktuurde, Mg-ryke ondergrande) in te sluit waarvoor dit vantevore as onbetraubaar beskou is.

O presente estudo propõe-se em investigar os componentes das crostas biológicas de solo (CBS) visando compreender o comportamento e as inter-relações das CBS em areais do Estado do Rio Grande do Sul (RS), no extremo meridional do Brasil. Pode ser entendido como uma análise exploratória de CBS existentes em nos areais do bioma Pampa, no sudoeste do RS, através de levantamento florístico e de características do solo. A pesquisa visa contribuir para estudos sobre o papel desse componente biótico na pedogênese e estabilidade da superfície de solos em áreas com processos de arenização. As amostras foram coletadas em maio de 2014 e 2015 em três locais, sendo duas por sítio, nos municípios de Alegrete e São Francisco de Assis. O sítio analisado em Alegrete se constitui de um areal recoberto por plantio de eucalipto, já os sítios em São Francisco de Assis se caracterizam por areais que sofrem processos de ravinamento, um sem interferência humana e o outro com ravina estabilizada artificialmente. As costas biológicas foram coletadas com placa de Petri invertida para garantir uma profundidade máxima de 2 cm e o mesmo volume para todas as amostras. A subsuperfície do solo também foi amostrada para análises texturais e químicas. A análise do material biológico foi realizada em estereoscópio e microscópio óptico (400-1.000x) onde verificou-se que a composição florística é constituída por 13 táxons de cianobactérias destacando-se espécies filamentosas, 2 táxons de líquens e um táxon de briófitas. Os resultados mostram que a sequência de sucessão se mostrou desde estágios primários – com manchas de cianobactérias – a táxons mais evoluídos com musgos de grande espessura. Foram observadas diferentes morfologias para as CBS, seguindo os padrões taxonômicos suave, rugoso, pinacular e ondulado. As amostras de solo sub-superficiais, confirmaram a textura arenosa e baixa fertilidade dos Neossolos Quartzarênicos Órticos nos sítios de estudo. Uma conclusão geral a partir dos estudos prévios, dos materiais analisados e das observações em campo corrobora afirmações de pesquisas que alertam para a elevada suscetibilidade dos solos destes locais do Rio Grande do Sul a processos erosivos hídricos e eólicos. / This study aims to investigate the biological soil crusts (BSC) components in order to understand the behaviour and the interrelations of BSC in some areais (sand deposits with no vegetation cover) of Rio Grande do Sul (RS), the southernmost Brazilian State. It can be understood as an exploratory analysis of existing BSC in Pampa geographic sites in southwestern RS through floristic survey and soil characteristics. The research aims to contribute to studies on the role of the biotic component in pedogenesis and stability of the soil surface in sites under sandification processes. The samples were collected in May 2014 and 2015 in three locations, two per site, in Alegrete and São Francisco de Assis. The analysed site in Alegrete constitutes a sandy terrain covered with eucalyptus plantation (29°42'35.48''S and 55°25'13.47"W), while the sites in São Francisco de Assis are characterized by sands that suffer processes of ravine, one without human intervention (29°30'54.98"S and 55°07'23.07"W) and the other with artificially stabilised ravine (29°23'58.85"S and 55°13'37.60"W). The biological crusts were collected with inverted Petri dish to ensure a maximum depth of 2 cm and the same volume for all samples. The soil subsurface was also sampled for textural and chemical analysis. The analysis of biological material was carried out in the stereoscope and optical microscope (400-1000x) where it was found that the floristic composition consists of 13 taxa of cyanobacteria highlighting filamentous species, 2 taxa of lichens and 1 taxon of bryophytes. The sequence of succession showed from early stages - with spots of cyanobacteria – to most advanced taxa with thick mosses. Different morphologies were observed for BSC, following the taxonomic patterns smooth, rough, pinacular and wavy. The subsurface soil samples confirmed the sandy texture and low fertility of the Psamments in the study sites. general conclusion from previous studies of the analysed materials and field observations corroborates research statements that warn of the high susceptibility of soils from these sites in Rio Grande do Sul to water and wind erosion, so this study recommends adoption of maximum care of soil conservation for whatever the intended use of the studied areas.

A fluidização é definida como a suspensão de partículas de um solo granular devido à ação de um fluxo ascendente, que cria uma força de arrasto suficiente para suportar o peso próprio das partículas, produzindo uma zona fluidizada. Neste trabalho são discutidos os mecanismos e os conceitos envolvidos na fluidização de solos arenosos com a utilização de jatos de água, que futuramente podem ser associados a novas tecnologias de instalação de ancoragens de plataformas de petróleo offshore. O estudo foi baseado em ensaios realizados em câmaras de calibração retangulares, com paredes em acrílico, preenchidas com areias de granulometria distintas, compactadas com densidade relativa de 50% e 100%. O sistema de jateamento consiste basicamente em uma bomba centrífuga que succiona a água armazenada em um reservatório e a conduz, através de um circuito hidráulico, à extremidade de tubos metálicos verticais, responsáveis pelo jateamento de água. Foram utilizados tubos com diferentes diâmetros e diversas velocidades de saída do jato. Iniciado o jateamento, tem-se a formação de um leito fluidizado, com formato côncavo e interface bem definida com a zona não fluidizada. O jato de água penetra certa profundidade no interior do leito fluidizado até ser defletido, no sentido ascendente, carregando partículas de areia que são depositadas ao redor da zona fluidizada. Após a formação de uma geometria fluidizada máxima, os tubos são reposicionados em uma nova profundidade. A fluidização ao longo da profundidade apresenta comportamento definido, com uma geometria inicialmente estável, que alcança uma condição de instabilidade em determinada profundidade, até sofrer sucessivos fechamentos, formando uma cavidade submersa fluidizada. Esta cavidade diminui de tamanho com o aumento da profundidade e a fluidização do solo deixa de ocorrer para certa profundidade de saída do jato. Os parâmetros principais que comandam a geometria da zona fluidizada aberta são a velocidade de saída e o diâmetro do jato, em conjunto com o tamanho das partículas do solo. Não foi observada influência da densidade relativa de compactação da areia na geometria fluidizada final. As dimensões geométricas são função do número densimétrico de Froude, cujo emprego permite a determinação de equações empíricas que descrevem o comportamento da geometria fluidizada aberta. O conjunto de ensaios de laboratório possibilitou determinar os parâmetros de controle dos mecanismos de fluidização em areias e a influência destes parâmetros no comportamento do solo fluidizado. / Fluidisation occurs when a granular soil is subjected to an upward fluid flow which creates a drag force sufficient to support the weight of the particles, producing a fluidised zone. In the present work a discussion is made on the mechanisms and concepts controlling the fluidised process produced by upflow washing in granular materials, aiming at the installation of offshore platform anchors. The study was carried out in laboratory rectangular calibration chambers filled with sand at relative densities ranging from 50% to 100%. The upflow washing was produced by a centrifuge pump that sucks water from a reservoir and conducts the water through a hydraulic system to the extremity of a vertical metalic tube, producing the water jet flow. Tubes with different diameters and fluid velocities have been used. The mechanism initiates with the formation of an open fluidised zone having a characteristic shape and distinct boundaries. The fluid penetrates up to a given depth and is deflected towards the surface. Once a stabilized zone is produced, the jet is lowered to another depth and the process is repeated. The shape of the fluidised zone changes with increasing jet depth from an open and stable approximately ellipsoidal form to an unstable spouted profile, and then to a submerged fluidised cavity. The shape of the cavity reduces with increasing depth. Parameters controlling the geometry of an open fluidised zone are fluid velocity and inside diameter of jet, together with diameter soil particles. There has been no influence of relative density in the geometry of the fluidised zone. In fact, this geometry is expressed by densimetric Froude number. The present work was usefull in demonstrating the parameters controlling fluidisation by upflow washing.

Sandy soils make up more than 205,000 ha in the coastal area of the North Central region of Vietnam. Thua Thien Hue province lying in the south of this region has predominantly sandy soils that cover almost 47,000 ha out of the 84,000 ha of cultivated land. Most of the population lives in the coastal area and people’s livelihoods are largely dependent on crop farming in these inherently poor soils. The objectives of this study were to provide extensive information on the soil and organic resources (including agricultural and aquatic sources) in the coastal area of Thua Thien Hue province, to assess the fertilization capacity of various organic materials when applied at different rates to soils for different crops and to make a diagnosis of the balance of main plant nutrients within the farms to assess possible risks of depletion in soils or of release to the environment. Soil characteristics were measured from a survey of 300 cultivated plots in seven villages scattered in the coastal area. All these light-textured soils are acidic and are very poor in organic C. Consequently, the cation exchange capacity is very low. Soil properties are linked significantly to the different cropping patterns. Farmers in the studied area use wide diversify of organic materials for various purposes. Very large variations in the content of major elements (C, N, P, K, Ca, and Mg) are observed in the organic samples. Crop yield and soil fertility increased following the rate of farmyard manure and organic amendment application. Organic amendments brought higher profit for rice and peanut growers in coastal sandy area. The highest fertilization efficiency was observed for pig manure in case of growing rice and peanut and goat manure for sweet potato. The most frequently used species of aquatic plants by local farmers are Najas indica, Vallisneria spiralis, Potamogeton malaianus plus various algae species. Najas Indica and Hydrilla verticillata showed the highest fertilization capacity. At farm level, the N, P, K balances in 10 studied farms were positive. More detailed N-P-K balances in 9 field plots indicated that N balance was largely positive for rice and sweet potato plots. P imports exceeded P exports in all studied plots, whereas K balance was always negative in 4 cropping systems.

No description available.

A field subirrigation experiment, using saline-sodic water, was carried out on a loamy sand soil in southwestern Quebec. The experimental field was divided into 16 plots with 4 treatments; saline-sodic water, "fresh" water, controlled drainage and non-irrigated. Each treatment had four replicates. Maize yield, hydraulic conductivity, salt concentration, and salt movement through the soil were recorded in all plots. / No significant difference in maize yield occurred between plots irrigated with saline-sodic or fresh water in any of the three years. Irrigated maize plots yielded approximately 30% more than non-irrigated plots. / Hydraulic conductivity reductions in the saline plots were noted in May 1986, after the first snowmelt. From statistical analysis carried out, it appears that the saline-sodic water had an effect on hydraulic conductivity, significant at the 0.05 level. / From the measurements taken from piezometer stations, located throughout the field, salt concentrations and salt movement through the saturated soil profile were determined. Using salt concentration data from both irrigation water and soil water, an average effective field porosity was calculated with a computer program. The results obtained were within 4% of those obtained in laboratory tests. Moreover, the program was then used to model the salt balance of the soil from May 85 to May 87. Results indicated that most salts were removed with the rainfall and snowmelt of the winter months of 85/86 and 86/87.

Field experiments were conducted on St-Samuel sandy loam soil in 1982 and 1983, with eight replicates of irrigated and non-irrigated maize plots. Soil moisture regime, root density and maize yields were determined to demonstrate the effect of subsurface irrigation and drainage systems. / Laboratory experiments were conducted on large and small undisturbed soil cores to determine pertinent soil properties, relating drainable volume and steady upward flux to water table depth. / A water balance model was developed and used with a stress-day-index to predict water table depth, excessive and deficit soil moisture conditions and effects on corn yield. Economic analyses were made to identify subsurface irrigation/drainage designs which optimize the profit for a corn crop. / A simple method based on first and second order moments was proposed to determine the effects of parameter uncertainty in the relationship of steady upward flux vs water table depth on subsurface irrigation/drainage design parameters. / Based on the above information, a realistic subsurface irrigation/drainage design was proposed and operational recommendations were made for an example field.

Traditionally, void ratio, e has been used as a state variable for predicting the liquefaction behaviour of soils under the Critical State (Steady State) framework. Recent publications show that void ratio, e may not be a good parameter for characterizing sand with fines as the steady state, SS data points move downward in e-log(p) space up to certain fines content termed as threshold fines content, TFC. Thus, it was difficult to apply SS concept on sand with fines as a small variation of fines content may lead to different SS line. Many researchers proposed to used equivalent granular void ratio, e* as an alternative state variable (i.e. in lieu of void ratio, e) in attempt to obtain a narrow trend line for SS data points irrespective of fc provided fc  TFC. The e* is obtained from e. For the conversion from e to e*, one need a parameter b which presents the active fraction of fines in overall force structure of sand. However, predicting the b is problematic. Most, if not all, of the b reported were determined by case-specific back-analysis, that is, the b-value was selected so that the test results for a given sand-fines type could be correlated with the equivalent granular void ratio, e* irrespective of fines content. This thesis examines the factors that affecting the b value by examining published work on binary packing. This leads to a simple semi-empirical equation for predicting the value of b based onparticle size ratio,  and fines content, fc. Published data and experimental results on Sydney sand appears to be in support of the proposed equation. The single relation of SS data points in e*-log(p) space for sand with fines is referred as Equivalent Granular Steady State Line, EG-SSL. The EG-SSL is then used to define the equivalent granular state parameter,*. A good correlation observed between * and q-p, q- q responses in undrained shearing. The e* and * are also used to modified a state dependent constitutive model. Seven model input parameters are needed in addition four to critical state input parameters. These parameters are obtained from drained test. The model is used to predict q-pand q- q responses for flow, non-flow and limited flow behaviour for 0% to 30% fines contents. The model predictions are in good agreement with experimental results. The effect of fines types (in terms of plasticity and angularity) on the prediction equation of b are also examined with four different types of fines. A negligible effect of fines type on the prediction equation of b is observed. The link between monotonic and cyclic loading behaviour for sand with fines are also examined with emphasis on cyclic instability and strain hardening behaviour after quasi steady state, QSS for a range of fines contents (provided that fc < TFC). It is found that a single set of rules could be used to correlate monotonic and cyclic behaviour for a range of fines contents at same *.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.