A study was made of the physical properties of a number of structurally sensitive soils some of which exhibited behaviour characteristic of hard-setting soils (soils which when wet slump and set hard, on drying presenting problems in terms of ease of cultivations and root growth). Work concentrated on an examination of soils of the Wick series at two sites at the Institute of Horticultural Research, Wellesbourne, where there is a documented history of consistent differences in crop yields between sites. The worse site (Big Ground) had been intensively managed for considerably longer than the better one (Plum Orchard). Dry bulk density measurements over the growing season suggest that slumping occurred on both sites. Big Ground had the greatest bulk density (typically over 1.65 g/cm3). Field and laboratory penetrometer measurements have shown that under relatively dry (an 8% moisture content) conditions roots would experience severe mechanical impedence on both sites. Root counts at final harvest showed that conditions for rooting were considerably worse in Big Ground where all roots were confined to the top 30 cm. Root growth was better in Plum Orchard and was concentrated in between peds, which did not exist at Big Ground. Laboratory strength (unconfined compressive and indirect tensile) and friability measurements on equilibrated samples also showed up differences between the two sites; the greates differences existing between 1 and 10 bar tension with Big Ground samples exhibiting the greatest strengths and least friabilities. On both sites strengths were observed to increase sharply for a comparatively small decrease in moisture content. Implications of these results are discussed with reference to ease of cultivation and rootability. Another light texured soil from Elgin, known for its tendency to erode, was chosen as a contrast to the Wellesbourne sites. Soil at this site was shown to have much less of a tendency to slump and to create problems for root growth, compared to the Wellesbourne sites. The Elgin soil was also considerably weaker, and the sharp increase in strength observed at Wellesbourne was not observed in Elgin. A new test for water suspendable solids, performed on the Wellesbourne and Elgin soils as well as on 5 other soils known for their structural instability showed that, with the exception of the Elgin soil, a large amount of silt sized material could be brought into suspension with little soild disturbance. An explanation for hard-setting behaviour which is based on those results is suggested.

No description available.

Soil chemical and physical properties are important to farm productivity, and they vary within fields, so farmers are interested in managing inputs like fertilizer according to local soil conditions within fields. Thus, they must have knowledge of soil conditions of interest, which have historically been measured at a few locations with tedious soil sampling and laboratory analyses. Advantageous to farmers would be a measurement method that provided more geographically detailed information at similar or lower cost. Remote and ground-based optical sensing are possibilities for gathering detailed soil information rapidly and inexpensively. This study considers the possibility of optically measuring soil characteristics. The first objective was to determine relationships between spectral reflectance in the 250- to 2500-nm range and the following soil constituents: clay, sand, Ca, K, Mg, Na, P, Zn, and acidity (pH). The second objective was to find wavebands for estimating certain soil properties, with the goal of sensor development. Physical, chemical, and spectral-reflectance measurements were made on 969 soil samples collected from two Mississippi fields over two years. Reflectances were averaged over 50-nm wavebands and analyzed with simple- and multiple-linear regression and canonical correlation in relation to soil properties. No single waveband was highly correlated to any soil property in this study, but waveband groups exhibited strong correlations with some soil properties. Clay was the only property consistently strongly correlated (R2 ¡Ý 0.50) to waveband groups over different fields and years. In general, waveband groups that were most highly correlated with a specific soil property in one field in one year were not similar to waveband groups most highly correlated with that property in a different field or year. Thus, it was difficult to select a waveband group for sensor development regarding a specific soil property. However, a group of nine promising wavebands was considered for estimating clay, and results for data in this study indicated the feasibility of grossly estimating clay content with spectral reflectance. Canonical correlation analysis demonstrated strong correlations among certain groups of soil-properties and wavebands. Clay appeared as the most promising property for sensor development from this portion of the study also.

Master of Science / Department of Agronomy / DeAnn Presley / In the Midwest there has been an increase in the number of vertical tillage (VT) implements sold and a large push in marketing these newer implements to producers. Vertical tillage is defined as shallow tillage, usually in the top 5 to 7.5 cm of the soil and results in no horizontal disturbance of the soil. The objective was to determine the short-term (one growing season) effects of a vertical-tillage operation on seedling emergence, crop growth and development, yield, residue decomposition, disease incidence and severity, quantification of pathogen propagules in soil and crop residue, and effects on the near-surface soil physical properties. The study was conducted during the 2010 and 2011 growing seasons at nine locations total for the two years throughout Kansas. The study compared vertical tillage against the producer’s current practice of no-till (NT), strip tillage (ST), or conventional disk (CD). Few significant differences were observed when studying soil properties, however not one treatment continuously had significant results and no trend was observed. Residue cover at all sites and across both years was significantly greater in the NT treatments. The residue cover also impacted the disease incidence and severity of Cercospora zea-maydis also known as gray leaf spot (GLS). Other diseases such as Marcophomina phaseolina and Fusarium spp. were not significantly impacted by one treatment or another. Overall, any differences in the soil, plant, and pathogen indicators have not resulted in significant yield improvements at any of the nine site locations of the two years of this study, but more site years will be needed to assess any potential benefits of VT. Information gained from this project will be disseminated to extension clientele including extension educators, producers, commodity groups, and agricultural professionals.

No description available.

Master of Science / Department of Agronomy / Michel D. Ransom / Soil is a dynamic resource that can undergo many changes due to altering conditions (Tugel et al., 2005). With that, humans can have a great effect on the conditions of a landscape and contribute to soil change. As soils change, the function of soils can be altered which would affect the ability of soils to support ecosystem services. The objective of this thesis is to access how management affects dynamic and inherent soil properties in western Kansas soils. Eight sites in Sheridan County, KS mapped as Keith 1-3% slopes (fine-silty, mixed, superactive, mesic Aridic Argiustolls) were described and sampled. Of the eight sites, four are in ST (ST) management and four are in no-till (NT) management. All sites have been irrigated under center pivot irrigation systems since the 1970s. Soil samples of the A horizon were taken at each site to analyze total carbon, aggregate stability, bulk density, pH and microbial respiration to assess the impacts of tillage management on dynamic soil properties. Additionally, pedons were described from the ST sites in the irrigated areas as well as outside the pivot track to represent dryland conditions. Particle size data, field descriptions, and the micromorphology of thin sections were analyzed to determine if the classification of Keith soils are affected by irrigation. Significant differences between NT and ST management were seen in microbial respiration, select water stable aggregate sizes, and pH and bulk density at certain depths. It was also found that irrigation did not affect clay illuviation nor carbonate leaching. Overall, it was concluded that inherent soil properties such as soil map unit composition and parent material can have a greater impact on soil change and prevent the recognition of changes in soil properties over a human time scale.

The annual production of biosolids in the Perth region during the period of this study was approximately 13,800 t dry solids (DS), being supplied by three major wastewater treatment plants. Of this, 70% was typically used as a low-grade fertiliser in agriculture, representing an annual land use area of around 1,600 ha when spread between 5 and 7 t DS/ha. Loading rates of biosolids are typically based on the nitrogen (N) requirements of the crop to be grown, referred to as the N Limiting Biosolids Application Rate (NLBAR). A consequence of using the NLBAR to calculate loading rates is that phosphorus (P) is typically in excess of plant requirement. The resultant high loading rates of P are considered in the guidelines developed for the agricultural use of biosolids in Western Australia, but lack research data specific to local conditions and soil types. Regulatory changes throughout Australia and globally to protect the environment from wastewater pollution have created a need for more accountable and balanced nutrient data. Experiments presented in this thesis were undertaken to ascertain: the percentage relative effectiveness (RE) of biosolids as a source of plant available P compared with inorganic P fertiliser; loading rates to best supply P for optimum crop growth; P loading rates of risk to the environment; and the forms of P in local biosolids. Therefore, both the agronomic and environmental viewpoints were considered. Anaerobically digested and dewatered biosolids produced from Beenyup Wastewater Treatment Plant, Perth with a mean total P content of 2.97% dry weight basis (db) were used in a series of glasshouse, field and laboratory experiments. The biosolids were sequentially fractionated to identify the forms of P present and likewise in soil samples after applying biosolids or monocalcium phosphate (MCP). / The biosolid P was predominantly inorganic (92%), and hence the organic fraction (8%) available for mineralisation at all times would be extremely low. The most common forms of biosolid P were water-soluble P and exchangeable inorganic P (66%), followed by bicarbonate extractable P (19%) and the remaining P as inorganic forms associated with Fe, Al and Ca (14%). Following the application of biosolids to a lateritic soil, the Fe and Al soil fractions sorbed large amounts of P, not unlike the distribution of P following the addition of MCP. Further investigation would be required to trace the cycling of biosolid P in the various soil pools. The growth response of wheat (Triticum aestivum L.) to increasing rates of biosolids and comparable rates of inorganic P as MCP, to a maximum of 150 mg P/kg soil was examined in the glasshouse. The percentage relative effectiveness (RE) of biosolids was calculated using fitted curve coefficients from the Mitscherlich equation: y = a (1-b exp–cx) for dry matter (DM) production and P uptake. The initial effectiveness of biosolid P was comparable to that of MCP with the percentage RE of biosolids averaging 106% for DM production of wheat shoots and 118% for shoot P uptake at 33 days after sowing (DAS) over three consecutive crops. The percentage residual value (RV) declined at similar rates for DM production in MCP and biosolids, decreasing to about 33% relative to freshly applied MCP in the second crop and to approximately 16% in the third crop. The effectiveness of biosolid P was reduced significantly compared with inorganic P when applied to a field site 80 km east of Perth (520 mm annual rainfall). An infertile lateritic podsolic soil, consistent with the glasshouse experiment and representative of a soil type typically used for the agricultural application of biosolids in Western Australia was used. / Increasing rates of biosolids and comparable rates of triple superphosphate (TSP), to a maximum of 145 kg P/ha were applied to determine a P response curve. The percentage RE was calculated for seasonal DM production, final grain yield and P uptake in wheat followed by lupin (Lupinus angustifolius L.) rotation for the 2001 and 2002 growing seasons, respectively. In the first year of wheat, the RE for P uptake in biosolids compared with top-dressed TSP ranged from 33% to 55% over the season and by grain harvest was 67%. In the second year, and following incorporation with the disc plough at seeding, the RE for P uptake by lupins in biosolids averaged 79% over the growing season compared with top-dressed TSP, and by grain harvest the RE was 60%. The residual value (RV) of lupins at harvest in biosolids compared with freshly applied TSP was 47%. The non-uniform placement of biosolids (i.e. spatial heterogeneity) was primarily responsible for the decreased ability of plant roots to absorb P. The P was more effective where biosolids were finely dispersed throughout the soil, less so when roughly cultivated and least effective when placed on the soil surface without incorporation. The RE for grain harvest of wheat in the field decreased from 67% to 39% where biosolids were not incorporated (i.e. surface-applied). The RE could also be modified by factors such as soil moisture and N availability in the field, although it was possible to keep these variables constant in the glasshouse. Consequently, absolute values determined for the RE need to be treated judiciously. Calculations showed that typical loading rates of biosolids required to satisfy agronomic P requirements of wheat in Western Australia in the first season could vary from 0 to 8.1 t DS/ha, depending on soil factors such as the P Retention Index (PRI) and bicarbonate available P value. / Loading rates of biosolids were inadequate for optimum P uptake by wheat at 5 t DS/ha (i.e. 145 kg P/ha) based on the NLBAR on high P sorbing soils with a low fertiliser history (i.e. PRI >15, Colwell bicarbonate extractable P <15 mg P/kg). On soils of PRI <2 mL/g however, biosolids applied at identical loading rates would result in high concentrations of available P. Further work on sites not P deficient would be necessary to validate these findings on farmed soils with a regular history of P fertiliser. The sieving of soil samples used in the field experiment to remove stones and coarse organic matter prior to chemical analysis inadvertently discarded biosolids particles >2 mm, and thus their was little relationship between soil bicarbonate extractable P and P uptake by plants in the field. The risk of P leaching in biosolids-amended soil was examined over a number of different soil types at comparable rates of P at 140 mg P/kg (as either biosolids or MCP) in a laboratory experiment. Given that biosolids are restricted on sites prone to water erosion, the study focussed on the movement of water-soluble P by leaching rather than by runoff of water-soluble P and particulate P. In general the percentage soluble reactive P recovered was lower in soils treated with biosolids than with MCP, as measured in leachate collected using a reverse soil leachate unit. This was particularly evident in acid washed sand with SRP measuring 14% for biosolids and 71% for MCP, respectively, although the differences were not as large in typical agricultural soils. Specific soil properties, such as the PRI, pH, organic carbon and reactive Fe content were negatively correlated to soluble reactive P in leachate and thus reduced the risk of P leaching in biosolids-amended soil. / Conversely, the total P and bicarbonate extractable P status of the soils investigated were unreliable indicators as to the amount of P leached. On the basis of the experiments conducted, soils in Western Australia were categorised according to their ability to minimise P enrichment and provide P necessary for crop growth at loading rates determined by the NLBAR. Biosolids applied at the NLBAR to soils of PRI >2mL/g with reactive Fe >200 mg/kg were unlikely to necessitate P loading restrictions. Although specific to anaerobically digested biosolids cake applied to Western Australian soils, the results will be of relevance to any industry involved in the land application of biosolids, to prevent P contamination in water bodies and to make better use of P in crop production.

No description available.

Wildfires result in altered landscape as well as altered soil properties. Wildfires result in conditions that are more susceptible to geotechnical hazards introducing a potential for cascading events in the surrounding area. Shallow landslides are common geohazards that result in a post-wildfire landscape. With an ever-increasing trend in wildfires, the need to better understand the impact wildfire-altered soil properties play on shallow slope instability is critical to evaluating risks to existing or planned development, mitigation of potentially hazardous conditions, prioritization of post-wildfire planning, and post-wildfire response preparation. The primary objective of this study is to provide a comprehensive overview of wildfire-altered geotechnical soil properties and their impact on rainfall-triggered landslides. For this purpose, laboratory and field testing has been performed on soil samples collected from four wildfire areas in California. In-situ hydraulic conductivity tests were performed on both burned and unburned soil. Soil samples collected from burned and unburned areas were tested in for index properties, shear strength, organic content, and pH. Results show that the mean angle of internal friction was reduced in burned soil samples for all study areas, the mean pH, organic content, and hydraulic conductivity were all greater in burned soils in all study areas, and cohesion was found to have contradicting trajectories. Resulting soil properties have been used to compare the factors of safety for representative unburned and burned slopes using a finite element seepage analysis and limit equilibrium slope stability analysis. The unburned and burn soil sample results are used to determine relative factors of safety for slope stability at each of the four wildfire areas. Peak historic and predicted precipitation have been used to further evaluate the relative factors of safety for pre and post-wildfire slope stability conditions. The comparative slope stability analysis has been used to provide a quantitative comparison of the role altered soil properties play on the potential for slope instability. Through this study, it is apparent that although soil properties are altered by wildfire, the impact altered soil properties have on the subsequent slope instability is much less than that of other contributing factors, including precipitation and root support.

No description available.