Amjad T Assi

Soil water thermodynamic to unify water retention curve by pressure plates and tensiometer

The pressure plate method is a standard method for measuring the pF curves, also called soil water retention curves, in a large soil moisture range from saturation to a dry state corresponding to a tension pressure of near 1500 kPa. However, the pressure plate can only provide discrete water retention curves represented by a dozen measured points. In contrast, the measurement of the soil water retention curves by tensiometer is direct and continuous, but limited to the range of the tensiometer reading: from saturation to near 70-80 kPa. The two methods stem from two very different concepts of measurement and the compatibility of both methods has never been demonstrated. The recently established thermodynamic formulation of the pedostructure water retention curve, will allow the compatibility of the two curves to be studied, both theoretically and experimentally. This constitutes the object of the present article. We found that the pressure plate method provides accurate measurement points of the pedostructure water retention curve h(W), conceptually the same as that accurately measured by the tensiometer. However, contrarily to what is usually thought, h is not equal to the applied air pressure on the sample, but rather, is proportional to its logarithm, in agreement with the thermodynamic theory developed in the article. The pF curve and soil water retention curve, as well as their methods of measurement are unified in a same physical theory. It is the theory of the soil medium organization (pedostructure) and its interaction with water. We show also how the hydrostructural parameters of the theoretical curve equation can be estimated from any measured curve, whatever the method of measurement. An application example using published pF curves is given.

Impact of brackish groundwater and treated wastewater on soil chemical and mineralogical properties

The long-term effect of using treated wastewater is not clearly defined: some researchers argue that it is better than freshwater for the soil health; others disapprove, claiming that irrigation with unconventional water resources causes soil degradation. This study assesses the impact of irrigation with non-traditional water on the chemical and mineralogical properties of a calcareous clayey soil from West Texas. The exponential rise in population and the realities of climate change contribute to the global increase in freshwater scarcity: non-conventional water sources, such as treated wastewater (TWW) and brackish groundwater (BGW), offer potentially attractive alternative water resources for irrigated agriculture. For this research, the differences between TWW and BGW were addressed by collecting and analyzing water samples for salt and nutrient content. Soil samples from three horizons (Ap, A, and B) were obtained from three different fields: Rainfed (RF), BGW irrigated, and TWW irrigated. Soil was analyzed for texture, salinity, sodicity, and carbon content. Clay mineralogy of the three different fields was analyzed using the B-horizons. The outcomes from the analysis showed that the BGW from the Lipan aquifer has higher salinity and is harder compared to TWW. Although the exchangeable sodium percentage (ESP), sodium adsorption ratio (SAR), and electroconductivity (EC) increased marginally compared to the control soil (RF), the soils were in good health, all the values of interest (SAR < 13, ESP < 15, pH < 8.5, and EC < 4) were low, indicating no sodicity or salinity problems. Smectite, illite, and kaolinite were identified in the three B-horizon samples using bulk X-ray diffraction (XRD). Overall, no major changes were observed in the soil. Thus, TWW and BGW are viable replacements for freshwater irrigation in arid and semi-arid regions.

The effect of municipal treated wastewater on the water holding properties of a clayey, calcareous soil

Wastewater reuse is a practice that has been gaining attention for the past few decades as the worlds population rises and water resources become scarce. Wastewater application on soil can affect soil health, and the manner and extent to which this occurs depends heavily on soil type and water quality. This study compared the long-term (15+ years) effects and suitability of using secondary-level treated municipal wastewater and brackish groundwater for irrigation on the water holding capacity of a clayey, calcareous soil on a cotton farm near San Angelo, Texas. The soil-water holding properties were determined from the extracted hydrostructural parameters of the two characteristic curves: water retention curve and soil shrinkage curve based on the pedostructure concept. In the pedostructure concept, these hydrostructural parameters are characteristic properties of the soil aggregates structure and its thermodynamic interactions with water. Results indicate that use of secondary treated wastewater increased available water capacity in the top horizon (0-15 cm) and decreased the available water holding capacity of this particular soil in the sub-horizons (15-72 cm). The brackish groundwater irrigation resulted in no effect on available water capacity in the top horizon, but significantly decreased it in the sub-horizons as well. The rainfed soil was the healthiest soil in terms of water holding capacity, but rainfall conditions do not produce profitable cotton yields. Whereas, treated wastewater irrigated soil is producing the highest yields for the farmer. Thus, this treated wastewater source and irrigation system can serve as a suitable irrigation alternative to using brackish groundwater, enhancing the water resource sustainability of this region.

Soil pedostructure-based method for calculating the soil-water holding properties

Graphical abstract

Current Water for Food Situational Analysis in the Arab Region and Expected Changes Due to Dynamic Externalities

Uneven distribution of water, food, and energy (WEF) resources, together with demographic, geographic, political, and other natural constraints, burden WEF security plans in many regions of the world. Decision makers are under pressure to bridge the WEF supply-demand gap, and often propose reactive, rather than preventive, strategies that are associated with uncertainty, challenges of sustainability, and various socio-economic, environmental, cultural, and political drawbacks. Arab countries, like most regions of the world, face internal and external challenges to managing, sustaining, and securing these scarce, unevenly distributed natural resources. According to the World Bank (2007), current management plans for addressing the WEF security challenges faced by the Arab countries fail to take into account the complicated internal and external dynamics of the region. This chapter looks holistically at the region and provides a situational analysis of the major stresses on WEF securities by specific location; it describes how these are impacted by externalities such as climate change, population growth, and economic development. The chapter explores the uncertainties associated with predicting the future of these external stresses and identifies management risks associated with the lack of understanding of the soil-water and associated spatial variability. The chapter concludes with a vision for adaptive management approaches that address the external stresses on regional WEF security, and offer a vision for increased resilience of local communities. The paper concludes by discussing ways to expand the vision and adapt it to offer a more general, broader security by localizing water and food securities.

Hydrostructural Pedology, New Scientific Discipline Allowing for Physical Modelling of ‘Green Water’ Dynamics in the Soil-Plant-Atmosphere System

Using a new paradigm of soil characterization and modeling in agro environmental sciences, named hydrostructural pedology, we were able to show that the “green water” concept of agronomists corresponds exactly to the pedostructural water concept which was physically defined in this paradigm. The water in the pedostructure of soils is composed of two types of water, named micro and macro, nested one in the other. They are differentiated by their chemical potential related to their position in the pedostructure: inside primary aggregates or outside of them in the interpedal space. A fundamental physics of the pedostructural water could be developed within this new paradigm. Finally, the soil medium can now be considered as the location in which the free water (named also blue water), coming from surface (rainfall, irrigation, etc.) and going down by gravity through the macro pore space of the soil, is partially absorbed by the pedostructure, and becomes Mini-review Article Braudeau et al.; JAERI, 15(3): xxx-xxx, 2018; Article no.JAERI.43822 2 then the ‘green water’ of the soil. Soil green water is, in fact, the soil water reserve available to plant roots and subsequently transpired by the plants into the canopy. The soil-water model Kamel ® , built according to this new paradigm, is the only model able to physically simulate the opposite dynamic cycles of these two kinds of water (blue and green) within the soil-plantatmosphere system, their exchanges and equilibrium states according to time, at each depth of the pedon. Important implications about strategy of soil-water characterization, mapping and modeling are given for sustainable development and management of agricultural zones.