Two BSC based indicators for rangeland condition assessment are species composition and cover. While there is strong agreement that BSC composition is a good indicator, there is less agreement that BSC cover alone is a good indicator. Although BSC have been included in previous remotely- sensed studies, their spectral characteristics, and hence their contributions to remotely-sensed spectral signatures, are not well known. / Data collection methods were refined for suitable method selection, stratification and site characterization, and morphological/functional group classification. Cover data of BSC were collected using a 100m line-intercept method on the stratified land units and statistical analyses were based on the cover variance analyses. Spectra of BSC groups were collected and characterized for different remote sensing indices. Five grazing gradient models based on collected spectra were developed for the evaluation of BSC effect on remotely-sensed data. Both existing and newly developed remote sensing indices were examined for BSC detection. / Sampling for cover of BSC in the field showed that there is indeed a detectable change with distance from water, suggesting that BSC cover can be used as an indicator of rangeland condition, provided that appropriate stratification of the study sites is carried out prior to sampling, and spectral differences in morphological and functional groups are taken into account. / Spectral analysis of BSC components showed that different classes of organisms in the crusts have different spectral characteristics, an din particular, that the (commonly-used) perpendicular vegetation index (PD54) is not suitable for detecting BSC. On the other hand, ground-level spectral modelling showed that the Normalized Difference Vegetation Index (NDVI) and Soil Stability Index (SSI) did show a distinguishable contribution from BSC. / A procedure for detecting cover of BSC was developed for image taken during the period after an effective rain, in contrast to the normal practice of selecting images of dry surfaces for interpretation. / The most suitable interval appears to be 2-4 days after rain in late autumn, winter and early spring. Of the existing indices, the SSI is the best for estimating cover of BSC from Landsat images. However, eight new indices, specifically designed for detection of BSC were developed during the course of this work. The best results were obtained for indices using the middle-infrared bands. / These results are promising for application to rangeland monitoring and suggest that BSC cover is an important indicator of rangeland condition if appropriate stratification, classification and data-collection methods are used. The effects of BSC cover on a remotely-sensed method are considerable, and thus they can not be neglected during image interpretation. There are different phenological patterns for BSC, annual and perennial elements, thus there is the possibility for the selection of imagery based on each phenological stage to detect these elements. Application of certain indices such as the PD54 may create mis-estimation of land covers. Although some of the existing and newly developed indices had significant results for BSC cover estimation, there is a requirement for a standalone remotely-sensed method to conclude the best index. / This thesis considers various aspects of the use of ground-based methods and remote sensing of Biological Soil Crusts (BSC). They are mostly distributed in winter rainfall dominated areas such as those at Middleback Field Centre (MFC) in South Australia. They can be used potentially as an indicator of rangeland condition by estimating grazing pressure (trampling). / Thesis (PhDEnvironmentalManagement)--University of South Australia, 2007.

Two BSC based indicators for rangeland condition assessment are species composition and cover. While there is strong agreement that BSC composition is a good indicator, there is less agreement that BSC cover alone is a good indicator. Although BSC have been included in previous remotely- sensed studies, their spectral characteristics, and hence their contributions to remotely-sensed spectral signatures, are not well known. / Data collection methods were refined for suitable method selection, stratification and site characterization, and morphological/functional group classification. Cover data of BSC were collected using a 100m line-intercept method on the stratified land units and statistical analyses were based on the cover variance analyses. Spectra of BSC groups were collected and characterized for different remote sensing indices. Five grazing gradient models based on collected spectra were developed for the evaluation of BSC effect on remotely-sensed data. Both existing and newly developed remote sensing indices were examined for BSC detection. / Sampling for cover of BSC in the field showed that there is indeed a detectable change with distance from water, suggesting that BSC cover can be used as an indicator of rangeland condition, provided that appropriate stratification of the study sites is carried out prior to sampling, and spectral differences in morphological and functional groups are taken into account. / Spectral analysis of BSC components showed that different classes of organisms in the crusts have different spectral characteristics, an din particular, that the (commonly-used) perpendicular vegetation index (PD54) is not suitable for detecting BSC. On the other hand, ground-level spectral modelling showed that the Normalized Difference Vegetation Index (NDVI) and Soil Stability Index (SSI) did show a distinguishable contribution from BSC. / A procedure for detecting cover of BSC was developed for image taken during the period after an effective rain, in contrast to the normal practice of selecting images of dry surfaces for interpretation. / The most suitable interval appears to be 2-4 days after rain in late autumn, winter and early spring. Of the existing indices, the SSI is the best for estimating cover of BSC from Landsat images. However, eight new indices, specifically designed for detection of BSC were developed during the course of this work. The best results were obtained for indices using the middle-infrared bands. / These results are promising for application to rangeland monitoring and suggest that BSC cover is an important indicator of rangeland condition if appropriate stratification, classification and data-collection methods are used. The effects of BSC cover on a remotely-sensed method are considerable, and thus they can not be neglected during image interpretation. There are different phenological patterns for BSC, annual and perennial elements, thus there is the possibility for the selection of imagery based on each phenological stage to detect these elements. Application of certain indices such as the PD54 may create mis-estimation of land covers. Although some of the existing and newly developed indices had significant results for BSC cover estimation, there is a requirement for a standalone remotely-sensed method to conclude the best index. / This thesis considers various aspects of the use of ground-based methods and remote sensing of Biological Soil Crusts (BSC). They are mostly distributed in winter rainfall dominated areas such as those at Middleback Field Centre (MFC) in South Australia. They can be used potentially as an indicator of rangeland condition by estimating grazing pressure (trampling). / Thesis (PhDEnvironmentalManagement)--University of South Australia, 2007.

Thesis (Ph. D.)--California Institute of Technology, 1985. / Typescript (photocopy). Includes bibliographical references (leaves 183-189).

In Venezuela rainfall-induced crust is the main problem in obtaining adequate stands of sesame (Sesamwn indicum L.) The effectiveness of seven commercially available soil conditioners to prevent soil crusting and their influence on sesame seedling emergence was tested on Parlo silt loam. The chemicals were sprayed on the soil surface at different rates and dilutions . The rates were established to give about the same treatment cost. Two chemica 1 s: a polyviny 1 aJ cohol (El vanol 71-30) and an anionic asphalt emulsion (Humofina B-2864) gave the greatest increase in sesame seedling emergence. Thereafter, the two chemicals were tested on two Utah soils (Parlo silt loam and Nib l ey silty c l ay loam) and four Venezuelan soils. Three of the Venezuelan soils (Turen silt loam , Nontilled Turen silt loam, and Agua Blanca si lty clay l oam) were sampled in areas actually being used for sesame production, but with problems of soil crusting. TI1e fourth Venezuelan soil (Guanipa sand) was collected in an area where sesame has recently been introduced.

Thesis (Ph. D.)--University of Adelaide, Dept. of Soil Science, 1995. / Includes bibliographical references.

Thesis (M.S.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 24, 2007) Vita. Includes bibliographical references.

Thesis (PhD) -- Stellenbosch University, 2003. / Please refer to full text to view abstract. / ENGLISH ABSTRACT: The effects of different land use practices on soil quality in South Africa were investigated in five contrasting biomes, with a particular emphasis on the tendency of soils to crust and soil C content. Soil quality is a nebulous concept and its applicability in the South African landscape is scrutinised. A wide range of chemical and physical soil properties were examined. The tendency of soils to crust was assessed using modulus of rupture, water dispersible clay and a new method of laboratory infiltration which was verified with rainfall simulation. Crusting was greater in bare, exposed soils than soils under vegetation and varied with soil parent material. Differences in crusting are explained by factors relating to clay dispersion such as clay mineralogy, soil C, labile or readily oxidisable C, concentration of soluble salts, soil texture and exchangeable Na percentage (ESP). Results from longterm bum plots in savanna and grassland revealed that annual burning can increase the tendency of soils to crust. Greater crusting in burnt plots is ascribed to greater dispersion of clay, which in tum is attributed to a decline in soil C, a decline in EC and an increase in ESP. The loss of nutrients from burnt plots over time is ascribed to removal of ash in surface runoff. Calcium, Mg, and K were lost more readily than Na probably because plants take up these nutrients in greater concentration than Na. The net effect was an increase in ESP. Crusting on burnt plots may be self-perpetuating, because increased runoff is likely to incsease the loss of soluble salts. Removal of vegetation due to cultivation, grazing or burning reduced soil C at all sites. Mean soil C in the 0-1 cm layer of unburnt plots in the Kruger National Park was more than three times greater than in burnt plots (2.7 vs 0.8%). The difference in soil C between treatments decreased with depth and illustrated that sampling to depths greater than a few centimetres can obscure effects of land use. The top few centimetres of soil have a disproportionate effect on soil infiltrability and nutrient cycling. This layer was named the pedoderm. Tree cover on burnt plots in the southern Kruger Nationa--l- Park is highly variable, and was hypothesised to be a function of herbivory pressure. Herbivores tended to congregate on plots with the greatest clay, Zn and Mn content and the lowest tree cover. It is suggested that soil properties determine the abundance of herbivores after fire, which in tum affects tree cover. In the Eastern Cape,intensive stocking with goats transforms dense thicket to an open savanna. Soils from goat-transformed sites had a greater tendency to crust than soils from intact thicket, probably due to aggregate weakening associated with a decline in soil C. Mean soil C content of intact thicket was almost double that of goat-transformed thicket (5.6 vs. 3% to a depth of 10 cm) and is exceptionally high for a semi-arid region. The potential to sequestrate carbon in degraded thicket landscapes is thus considerable. Managing the land for greater sequestration of C will have the added benefit of increasing soil aggregate stability, reducing the tendency of soils to crust and therefore increasing the rate of water infiltration through the pedoderm. The benefits of such an approach have been recognised by specialists in soil conservation and rural land use for many decades, based largely on empirical observation. The results of this thesis provide a more quantitative basis for appreciating the effects of soil C across a broad spectrum of South African biomes. / AFRIKAANSE OPSOMMING: Die invloed van verskillende landgebruikspraktyke op grondkwaliteit in Suid-Afrika is in vyf kontrasterende biome ondersoek met spesifieke klem op die neiging van gronde om korste te vorm en die grond koolstofinhoud. Grondkwaliteit is 'n vae konsep en die toepassing daarvan in die Suid-Afrikaanse grondlandskap is noukeurig ondersoek. 'n Wye reeks van chemiese en fisiese grondeienskappe is ondersoek. Die neiging van korsvorming by gronde is beraam deur die gebruik van breukmodulus, waterdispergeerbare klei en 'n nuwe metode van laboratorium-infiltrasie wat met behulp van reënvalsimulasie gekontroleer is. Korsvorming was groter in kaal, blootgestelde gronde as in gronde met 'n plantbedekking en het gewissel volgens moedermateriaal. Verskille in korsvorming word verklaar deur faktore wat verband hou met kleidispergering soos byvoorbeeld kleimineralogie, grondkoolstof, labiele of maklik oksideerbare koolstof, konsentrasie oplosbare soute, grondtekstuur en uitruilbare natriumpersentasie (UNP). Resultate van langtermyn brandpersele in savanna en grasland het getoon dat jaarlikse brand die neiging tot korsvorming kan verhoog. Meer korsvorming in brandpersele word toegeskryf aan groter kleidispergering, wat waarskynlik verband hou met 'n afname in grondkoolstof, 'n afname in elektriese geleiding (Be) en 'n toename in UNP. Plantvoedingstowwe gaan oor tyd verlore uit brandpersele, waarskynlik deur die verwydering van as in oppervlak afloop. Kalsium, Mg en K gaan meer geredelik verlore as Na, waarskynlik omdat plante hierdie voedingstowwe in groter hoeveelhede opneem as Na. Die netto effek is 'n toename in UNP. Korsvorming op brandpersele kan self instand gehou word omdat verhoogde afloop die moontlike verlies van oplosbare soute kan verhoog. Verwydering van plantegroei deur bewerking, beweiding of brand het grondkoolstof op alle plekke verlaag. Die gemiddelde grondkoolstof in die 0-1 cm laag van ongebrande persele in die Kruger Nasionale Park was meer as drie maal groter as in --.. brandpersele (2.7 vs 0.8 %). Die verskil in grondkoolstof tussen behandelings neem af met diepte wat daarop dui dat monsterneming tot dieptes groter as 'n paar sentimeters die effek van landgebruik kan verberg. Die boonste paar sentimeters van 'n grond het 'n oneweredige invloed op infiltrasie en voedingstofsirkulasie. Hierdie laag word die pedoderm genoem. Boombedekking op brandperseie in die suidelikeKruger Nasionale Park is hoogs variërend. Die hipotese was dat dit 'n funksie van druk deur planteters is. Planteters neig om op persele met die hoogste klei, Zn- en Mn-inhoud en die laagste boom bedekking te versamel. Daar word voorgestel dat grondeienskappe die hoeveelheid planteters na 'n brand bepaal. Dit beïnvloed op sy beurt weer die boombedekking. In die Oos-Kaap het intensiewe bokboerdery digte bosruigtes verander na oop savannas. Gronde van bok-veranderde lokaliteite het 'n groter neiging tot korsvorming as gronde van onveranderde bosruigtes, vermoedelik as gevolg van verswakking van aggregate met 'n. afname in grondkoolstof. Die gemiddelde grondkoolstof van onveranderde bosruigtes was byna dubbel soveel as die koolstof van bok-veranderde bosruigtes (5.6 vs 3 % tot 'n diepte van 10 cm) en buitengewoon hoog vir 'n semi-ariede streek. Die potensiaal vir koolstof sekwestrasie in degradeerde bosruigte landskappe is dus aansienlik. Bestuur van land vir groter sekwestrasie van koolstof het die bykomende voordeel van verhoogde grond aggregaatstabilteit, verlaging van die neiging tot korsvorming en daardeur 'n verhoging in die tempo van waterinfiltrasie deur die pedoderm. Die voordele van so 'n benadering is vir baie dekades deur spesialiste in grondbewaring en landelike landgebruik herken. Dit was grootliks gebaseer op empiriese waarneming. Die resultate van hierdie tesis bied 'n meer kwantitatiewe basis tot die verstaan van die invloed van grondkoolstof oor 'n breë spektrum van Suid-Afrikaanse biorne.

The effects of sulfur-containing amendments (H₂SO₄,Al₂(SO₄)₃ and gypsum) or crust formation, soil chemical properties, seedling emergence and yields of onions (Allium cepa), tomatoes (Lycopersicum esculentum) and chili peppers (Capsicum sp.) were studied on a Pima clay loam soil. Treatments were surface applied on a strip above the seeds. The chemicals influenced the penetrometer index, soil-pH, electrical conductivity, DPTA-extractable soil Fe, Cu, Zn, Mu and seedling emergence in two greenhouse experiments. Gypsum and H₂SO₄ increased seedling emergence while Al₂(SO₄)₃ reduced the soil-pH and EC more than H₂SO₄ and gypsum. Based upon penetrometer readings, H₂SO₄ was the best anti-crusting agent tested followed by gypsum and Al₂(SO₄)₃. At the end of the study, all soil samples were very low in KCl extractable Al, showing that Al toxicity was not responsible for seedling damage. Gypsum decreased levels of Mn and Zn but did not affect Fe and Cu. Al₂(SO₄)₃ increased Fe and Zn, decreased Cu but did not affect Mn. H₂SO₄ did not affect extractable Mn, Cu, Zn and Fe levels. In a field study using two water qualities at Safford, gypsum produced the most tomato seedlings whereas Al₂(SO₄)₃ and H₂SO₄ produced the least. Onion stand counts were not affected by the chemicals with either water. Gypsum, H₂SO₄ and Al₂(SO₄)₃ polymer produced the highest pepper stand counts with the saltier water but there were no differences with lower salt water. Tomatoes produced the highest yield with gypsum and lowest with H₂SO₄ and Al₂(SO₄)₃ with saltier water. With lower salt water, gypsum produced highest yield, followed by the H₂SO₄. Both H₂SO₄ treatments produce low yields. Onions showed no treatment response under lower salt water, while with saltier water, gypsum and H₂SO₄ produced the highest yields. Pepper yields were not affected by amendments with the lower salt water. Al₂(SO₄)₃ polymer, H₂SO₄ and gypsum increased yields with the saltier water. Varieties of peppers and tomatoes produced different yields in response to water quality in a supplementary field study.

Includes bibliographical references. The beneficial effects of tillage are often negated in Australian soils by poor aggregate structural stability. If irrigation or rain falls on exposed freshly tilled soil, crusting or harsetting often develops on drying. Rainfall intensity, kinetic energy, rate of wetting, antecedent water content and soil management history have been implicated in aggregate breakdown.

Includes bibliographical references. / xxiv, 177 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The beneficial effects of tillage are often negated in Australian soils by poor aggregate structural stability. If irrigation or rain falls on exposed freshly tilled soil, crusting or hardsetting often develops on drying. Rainfall intensity, kinetic energy, rate of wetting, anticedent water contentand soil management history have been implicated in aggregate breakdown. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1995