A Constitutive Model for Overconsolidated Structured Soils Using Structural Variable

Due to the influence of soil structure, structured soils exhibit significantly different mechanical behavior compared to the reconstituted soils having the same material. In this work, a theoretical analysis focusing on the mechanical behavior of structured soils is presented. Based on the mechanical behavior of the structured soil, a newly defined variable structural index was used as a measurement of the integrity of soil structure based on the concept of intrinsic compression line of intact structured soils. Furthermore, a novel correlation for the variation in volume of structured soils is established using effective stress and newly defined structural index as the constitutive variables. The novel correlation provided interpretation about the mechanism of compression behavior of the structured soils. Afterwards, the proposed correlation for the variation in volume was extended to triaxial stress state in the framework of subloading surface to include the effect of overconsolidation. Comparisons between the predictions and experimental results validated the proposed constitutive model for structured soils.

Duncan Joseph Greenwood. 16 October 1932 — 13 February 2010

During his 55-year career as a highly distinguished scientist, Duncan Greenwood made a major contribution to the field of soil science and plant nutrition. His early studies on soil aeration revolutionized thinking on the mechanisms by which oxygen influences the activity of microorganisms and their metabolism of organic substances in structured soil. His ideas resulted in the ‘micro-site concept of soil aeration’, which is still widely accepted today. Later he turned his attention to the nutritional requirements of vegetable crops at a time when the horticultural industry was starting to introduce inorganic fertilizers. He developed a novel static model of N, P and K response, which he used to produce the first scientifically based inorganic fertilizer recommendations for 23 different vegetable crops. Not satisfied with this major development, Duncan started to create more sophisticated dynamic models using novel widely applicable relationships that took more account of the effects of weather on nutrient behaviour in the soil and plant. He not only used these to provide important insights into many of the complex interacting processes involved, but also incorporated them into some of the first computer-based decision support systems for practical site-specific fertilizer advice for the vegetable growing industry. The application of these advances had an important effect on the efficiency of crop production and the reduction of associated environmental impacts. Duncan continued to devise new models for nutrient and water use throughout the rest of his career and to explore ways of applying them in different areas of soil and crop science.

Use of Soil-Structured Capillary Barrier can Mitigate the Impact of Saline-Irrigation Water on Marigold Grown Under Field Condition

Capillary barriers (CBs) as engineered porous composites is novel and promising technology for mitigating salinity and drought stress of plants. This study aimed to imitate a naturally formed CB structure recently discovered in the reservoir bed of Al-Khoud dam at the Governorate of Muscat in northern Oman and to test the impact of this unique CB on mitigating the salinity stress of marigold plants grown under an open field condition. A plot was constructed and divided into “structured” (engineered cascade CB design) and “unstructured” soils and planted with marigold (Tagetes erecta) plants that were subjected to four salinity treatments (control with ECi ≈ 0.6 dS m-1 ; 3 dS m-1; 6 dS m-1; and 9 dS m-1). Plant physiological, vegetative, and reproductive growth parameters were measured in each treatment. The results showed that the structured soil significantly saved irrigation water and reduce salts accumulation. Structured soil improved all vegetative and reproductive plant parameters measured and helped in reducing the effects of salinity stress on the growth and production of the marigold under arid-climate field conditions. The results also showed the capability of structured soil in water saving and improving water use efficiency. This study substantiates a novel method in mitigating salinity problem and in water saving in arid and semi-arid regions, in particular in Oman. Further studies are required to test the use of the engineered cascade CB design with different crops and with alternative (e.g. subsurface) irrigation methods.

Test of possible standard samples for soil physical analyses

<p>As they mostly deal with undisturbed samples, soil hydrophysics analyses often present variability in their results. No one can deny that soil, and particularly structured soil, is a very complex and challenging media to describe. But it remains that the lab measurements themselves deserve attention. To what extent are they reproducible? To what extent different labs following the same protocol do they provide the same results for a given soil sample? Is this uncertainty quantifiable? Is there a way to standardize or harmonize the analyses? And of course, to what extent does it really matter when it comes to produce reliable information about i.e. drought consequences?</p><p>When most of the labs related to chemical analyses can rely on ring tests to improve their capacity, soil physics labs can’t. Building reference samples that could fit into classical measurement devices is one of the options that could allow to run ring tests in soil physics measurements.</p><p>The poster will present an attempt to develop reference samples in view to measure the wet end of the retention curve.</p>