Heat and Moisture Conduction in Unsaturated Soils

Mathematical models are developed for the prediction of heat transfer from hot water pipes buried in the soil. Heat transfer in the absence of moisture transfer is described as a function of the difference between the temperature of the pipe and the temperature of the soil surface. The energy balance is used to determine the longitudinal temperature distribution of the water. The method is extended to describe a system of equally spaced, parallel buried pipes. Soil temperature profiles around the pipes are presented. The model is used to calculate the land area that can be heated by an underground piping system carrying cooling water from the condensers of a 1000 MW nuclear-electric plant. A new development of the phenomenological equations for coupled heat and moisture flow, based on the theory of Irreversible Thermodynamics, is presented. Solutions of the equations for boundary conditions representative of buried piping systems designed for simultaneous soil heating and irrigation are presented

Source-tracking cadmium in New Zealand agricultural soils: a stable isotope approach

Cadmium (Cd) is a toxic heavy metal, which is accumulated by plants and animals and therefore enters the human food chain. In New Zealand (NZ), where Cd mainly originates from the application of phosphate fertilisers, stable isotopes can be used to trace the fate of Cd in soils and potentially the wider environment due to the limited number of sources in this setting. Prior to 1997, extraneous Cd added to soils in P fertilisers was essentially limited to a single source, the small pacific island of Nauru. Analysis of Cd isotope ratios (ɛ114/110Cd) in Nauru rock phosphate, pre-1997 superphosphate fertilisers, and Canterbury (Lismore Stony Silt Loam) topsoils (Winchmore Research Farm) has demonstrated their close similarity with respect to ɛ114/110Cd. We report a consistent ɛ114/110Cd signature in fertiliser-derived Cd throughout the latter twentieth century. This finding is useful because it allows the application of mixing models to determine the proportions of fertiliser-derived Cd in the wider environment. We believe this approach has good potential because we also found the ɛ114/110Cd in fertilisers to be distinct from unfertilised Canterbury subsoils. In our analysis of the Winchmore topsoil series (1949-2015), the ɛ114/110Cd remained quite constant following the change from Nauru to other rock phosphate sources in 1997, despite a corresponding shift in fertiliser ɛ114/110Cd at this time. We can conclude that to the present day, the Cd in topsoil at Winchmore still mainly originates from historical phosphate fertilisers. One implication of this finding is that the current applications of P fertiliser are not resulting in further Cd accumulation. We aim to continue our research into Cd fate, mobility and transformations in the NZ environment by applying Cd isotopes in soils and aquatic environments across the country

The feasibility of subirrigation systems on claypan soils in the Midwest

This was a study to evaluate the suitability of subirrigation along with alternative soil and water trujlnagement practices on claypan soil. Crop yields on these soils are usually low because of limited water management for crop production. Several years of crops, soil and weather data collected on a claypan soil in Illinois were used to study performance of subirrigation and conventional irrigation on these soils. Various drain spacings and depth combinations for both good and poor· quality surface drainage were simulated. Results indicated that optimum drain spacing for subirrigation on these soils would be 6 m under good surface drainage, and a weir setting depth of 35 cm on a 5-year recurrence interval basis. However, such a close drain spacing may not be economically feasible.U.S. Geological SurveyU.S. Department of the InteriorOpe

Opportunities for improving irrigation efficiency with quantitative models, soil water sensors and wireless technology

Increasingly serious shortages of water make it imperative to improve the efficiency of irrigation in agriculture, horticulture and in the maintenance of urban landscapes. The main aim of the current review is to identify ways of meeting this objective. After reviewing current irrigation practices, discussion is centred on the sensitivity of crops to water deficit, the finding that growth of many crops is unaffected by considerable lowering of soil water content and, on this basis, the creation of improved means of irrigation scheduling. Subsequently, attention is focused on irrigation problems associated with spatial variability in soil water and the often slow infiltration of water into soil, especially the subsoil. As monitoring of soil water is important for estimating irrigation requirements, the attributes of the two main types of soil water sensors and their most appropriate uses are described. Attention is also drawn to the contribution of wireless technology to the transmission of sensor outputs. Rapid progress is being made in transmitting sensor data, obtained from different depths down the soil profile across irrigated areas, to a PC that processes the data and on this basis automatically commands irrigation equipment to deliver amounts of water, according to need, across the field. To help interpret sensor outputs, and for many other reasons, principles of water processes in the soil–plant system are incorporated into simulation models that are calibrated and tested in field experiments. Finally, it is emphasized that the relative importance of the factors discussed in this review to any particular situation varies enormously

Inversion algorithms for the microwave remote sensing of soil moisture. Experiments with swept frequency microwaves

Two experiments were performed employing swept frequency microwaves for the purpose of investigating the reflectivity from soil volumes containing both discontinuous and continuous changes in subsurface soil moisture content. Discontinuous moisture profiles were artificially created in the laboratory while continuous moisture profiles were induced into the soil of test plots by the environment of an agricultural field. The reflectivity for both the laboratory and field experiments was measured using bi-static reflectometers operated over the frequency ranges of 1.0 to 2.0 GHz and 4.0 to 8.0 GHz. Reflectivity models that considered the discontinuous and continuous moisture profiles within the soil volume were developed and compared with the results of the experiments. This comparison shows good agreement between the smooth surface models and the measurements. In particular the comparison of the smooth surface multi-layer model for continuous moisture profiles and the yield experiment measurements points out the sensitivity of the specular component of the scattered electromagnetic energy to the movement of moisture in the soil

Some aspects of soil physics applicable to trickle irrigation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Soil Science at Massey University

Irrigation of crops is one of the more widely used techniques to increase yeilds. Trickle irrigation is one such method and is more suited to horticultural crops. In New Zealand, with horticulture assuming more importance, appropriate methods of design and operation of trickle irrigation systems are required. In this study a simple approximation to Wooding's solution for steady infiltration from a shallow ponded source, much like that found under trickle emitters is examined. This may aid in irrigation design and practice. The approximation also allowed for the development of a method to concurrently measure the saturated hydraulic conductivity and sorptivity from simple field infiltration measurements with a minimum of soil disturbance. Saturated hydraulic conductivities and sorptivities are of great use in soil water studies in general. A commercial trickle irrigation system was also examined to determine the suitability of such irrigation systems to particular soils, and to examine the present irrigation scheduling. The approximation to Wooding's solution was found to perform well in the field in many respects, particularly in determining steady ponded zone sizes. Ponded zone sizes are important in that they control the volume of soil wetted by irrigation to a large degree. Much of this agreement is due to the use of parameters determined by the simple field method developed from this theory. Sorptivities and saturated hydraulic conductivities obtained by this method were found to be more realistic for trickle irrigation than those determined by other existing methods. Systematic errors in these other methods, mainly soil disturbance and the concomitant creation of continuous flow paths for water, as well as soil smearing, are thought to be the main cause of this difference. Temporal and spatial variation in soil physical properties are however, found to hinder the use of soil physics theory in the field. Macropores (due to soil biological activity) were found to profoundly influence infiltration processes and soil-water distribution. These effects were particularly marked for the site with a commercial trickle irrigation system. Here the efficiency of the present system is thought to be low, and evidence indicates that irrigation was in excess of plant requirements. The utility of Wooding's solution, and the method to measure soil physical parameters developed from this, is further demonstrated in this orchard