Simulating the interaction between plant roots, soil water and nutrient flows, and barriers and objects in soil using rootmap

Abstract: Plant productivity is directly affected by the capacity of the root system to forage for soil resources. An enhanced understanding of root-soil interactions provides the potential to improve crop performance in specific soil environments. Interactions between roots and soil are, however, complex. The root-soil environment is heterogeneous and difficult to visualise and measure, root architecture and root growth responses are complex and dynamic, and processes from the ionic and rhizosphere scale right up to the whole crop and even catchment scale are involved. For these reasons, pot experiments are used in root studies to simplify the environment, target specific interactions and aid with visualisation and measurement. Significant challenges exist, however, in relating pot studies to the field, requiring upscaling from a spatially confined and artificially contrived environment to the reality of a more complex cropping environment. Simulation models provide an opportunity to upscale complex root-soil interactions from the pot to the field, but to do so they must represent the way that plant roots explore a restricted pot environment. In this study ROOTMAP, a 3D functional-structural model of root growth and resource capture, was modified to enable the simulation of barriers in soil, and the interaction of plant roots and soil water and nutrients with those barriers. This barrier-modelling utilises custom coding, with the support of Boost.Geometry (Generic Geometry Library) where appropriate. The barrier approach defines the 3D shape and location of any number of what are termed Volume Objects. Roots and soil can be: wholly contained within one Volume Object such as in the case of roots growing in a pot; a plant can have roots distributed between two Volume Objects such as in a split-pot experiment; and they can be wholly outside one or more Volume Objects for simulating the presence of rocks or other hard objects in soil. Volume Objects can be wholly impermeable, such as; pot walls that contain roots within them, or impermeable rocks or hardpan layers that roots grow around. Volume Objects can also have varying degrees of permeability for representing layers or areas in soil that have varying degrees of hardness and varying root penetrability. In this initial version of the code, barriers or objects can be represented as rectangular prisms, giving flat barrier layers or square or rectangular objects such as root/rhizo boxes, or as cylinders, representing curved pots or smooth curved objects in soil. The barrier modelling code calculates the deflection of a root tip when it intersects a boundary, representing the way that plant roots grow around and along object surfaces. It also calculates the effect of semi-permeable objects in soil on root growth into and around those objects. Water and nutrients are distributed through the soil environment by use of a variable 3D grid of sub-volumes or cells. The water and nutrient routines then search for the presence of a barrier or wall (Volume Object) intersecting each cell and the volume of the cell contained inside/outside the barrier is calculated. This combined with the permeability of the barrier determines the water and nutrient transfer within the cell. The result is a model which can simulate the root, water and nutrient dynamics in a bounded-environment. This provides an opportunity to represent root architectural development and root-soil interactions in pots and rhizo-boxes, and investigate how these studies relate to root growth and resource capture in un-bounded field soil

Measuring root system traits of wheat in 2D images to parameterize 3D root architecture models

Background and aimsThe main difficulty in the use of 3D root architecture models is correct parameterization. We evaluated distributions of the root traits inter-branch distance, branching angle and axial root trajectories from contrasting experimental systems to improve model parameterization.MethodsWe analyzed 2D root images of different wheat varieties (Triticum aestivum) from three different sources using automatic root tracking. Model input parameters and common parameter patterns were identified from extracted root system coordinates. Simulation studies were used to (1) link observed axial root trajectories with model input parameters (2) evaluate errors due to the 2D (versus 3D) nature of image sources and (3) investigate the effect of model parameter distributions on root foraging performance.ResultsDistributions of inter-branch distances were approximated with lognormal functions. Branching angles showed mean values <90°. Gravitropism and tortuosity parameters were quantified in relation to downwards reorientation and segment angles of root axes. Root system projection in 2D increased the variance of branching angles. Root foraging performance was very sensitive to parameter distribution and variance.Conclusions2D image analysis can systematically and efficiently analyze root system architectures and parameterize 3D root architecture models. Effects of root system projection (2D from 3D) and deflection (at rhizotron face) on size and distribution of particular parameters are potentially significant

A qualitative study of naturopathy in rural practice: A focus upon naturopaths' experiences and perceptions of rural patients and demands for their services

Background. Complementary and alternative medicine (CAM) use - of which naturopathy constitutes a significant proportion - accounts for approximately half of all health consultations and half of out-of-pocket expenditure in Australia. Data also suggest CAM use is highest amongst rural Australians. Unfortunately little is known about the grass-roots reality of naturopathy or other CAM use in rural regions. Methods. Semi-structured interviews were conducted with 20 naturopaths practising in the Darling Downs region of South-East Queensland to assess their perceptions and experiences of rural patients and demand for their services. Results. Naturopaths described strong demand in rural areas for their services and perceived much of this demand as attributable to cultural traits in rural communities that served as pull factors for their naturopathic services. Such perceived traits included a cultural affinity for holistic approaches to health and disease and the preventive philosophy of naturopathy and an appreciation of the core tenet of naturopathic practice to develop closer therapeutic relationships. However, cost and a rural culture of self-reliance were seen as major barriers to naturopathic practice in rural areas. Conclusions. Demand for naturopathic services in rural areas may have strong underlying cultural and social drivers. Given the apparent affinity for and increasingly large role played by CAM services, including naturopathic medicine, in rural areas it is imperative that naturopathic medicine and the CAM sector more broadly become a core focus of rural health research

Mechanistic framework to link root growth models with weather and soil physical properties, including example applications to soybean growth in Brazil

Background and aimsRoot elongation is generally limited by a combination of mechanical impedance and water stress in most arable soils. However, dynamic changes of soil penetration resistance with soil water content are rarely included in models for predicting root growth. Better modelling frameworks are needed to understand root growth interactions between plant genotype, soil management, and climate. Aim of paper is to describe a new model of root elongation in relation to soil physical characteristics like penetration resistance, matric potential, and hypoxia.MethodsA new diagrammatic framework is proposed to illustrate the interaction between root elongation, soil management, and climatic conditions. The new model was written in Matlab®, using the root architecture model RootBox and a model that solves the 1D Richards equations for water flux in soil. Inputs: root architectural parameters for Soybean; soil hydraulic properties; root water uptake function in relation to matric flux potential; root elongation rate as a function of soil physical characteristics. Simulation scenarios: (a) compact soil layer at 16 to 20 cm; (b) test against a field experiment in Brazil during contrasting drought and normal rainfall seasons.Results(a) Soil compaction substantially slowed root growth into and below the compact layer. (b) Simulated root length density was very similar to field measurements, which was influenced greatly by drought. The main factor slowing root elongation in the simulations was evaluated using a stress reduction function.ConclusionThe proposed framework offers a way to explore the interaction between soil physical properties, weather and root growth. It may be applied to most root elongation models, and offers the potential to evaluate likely factors limiting root growth in different soils and tillage regimes

Financial incentives for return of service in underserved areas: a systematic review

<p>Abstract</p> <p>Background</p> <p>In many geographic regions, both in developing and in developed countries, the number of health workers is insufficient to achieve population health goals. Financial incentives for return of service are intended to alleviate health worker shortages: A (future) health worker enters into a contract to work for a number of years in an underserved area in exchange for a financial pay-off.</p> <p>Methods</p> <p>We carried out systematic literature searches of PubMed, the Excerpta Medica database, the Cumulative Index to Nursing and Allied Health Literature, and the National Health Services Economic Evaluation Database for studies evaluating outcomes of financial-incentive programs published up to February 2009. To identify articles for review, we combined three search themes (health workers or students, underserved areas, and financial incentives). In the initial search, we identified 10,495 unique articles, 10,302 of which were excluded based on their titles or abstracts. We conducted full-text reviews of the remaining 193 articles and of 26 additional articles identified in reference lists or by colleagues. Forty-three articles were included in the final review. We extracted from these articles information on the financial-incentive programs (name, location, period of operation, objectives, target groups, definition of underserved area, financial incentives and obligation) and information on the individual studies (authors, publication dates, types of study outcomes, study design, sample criteria and sample size, data sources, outcome measures and study findings, conclusions, and methodological limitations). We reviewed program results (descriptions of recruitment, retention, and participant satisfaction), program effects (effectiveness in influencing health workers to provide care, to remain, and to be satisfied with work and personal life in underserved areas), and program impacts (effectiveness in influencing health systems and health outcomes).</p> <p>Results</p> <p>Of the 43 reviewed studies 34 investigated financial-incentive programs in the US. The remaining studies evaluated programs in Japan (five studies), Canada (two), New Zealand (one) and South Africa (one). The programs started between 1930 and 1998. We identified five different types of programs (service-requiring scholarships, educational loans with service requirements, service-option educational loans, loan repayment programs, and direct financial incentives). Financial incentives to serve for one year in an underserved area ranged from year-2000 United States dollars 1,358 to 28,470. All reviewed studies were observational. The random-effects estimate of the pooled proportion of all eligible program participants who had either fulfilled their obligation or were fulfilling it at the time of the study was 71% (95% confidence interval 60–80%). Seven studies compared retention in the <it>same </it>(underserved) area between program participants and non-participants. Six studies found that participants were less likely than non-participants to remain in the same area (five studies reported the difference to be statistically significant, while one study did not report a significance level); one study did not find a significant difference in retention in the same area. Thirteen studies compared provision of care or retention in <it>any </it>underserved area between participants and non-participants. Eleven studies found that participants were more likely to (continue to) practice in any underserved area (nine studies reported the difference to be statistically significant, while two studies did not provide the results of a significance test); two studies found that program participants were significantly less likely than non-participants to remain in any underserved area. Seven studies investigated the satisfaction of participants with their work and personal lives in underserved areas.</p> <p>Conclusion</p> <p>Financial-incentive programs for return of service are one of the few health policy interventions intended to improve the distribution of human resources for health on which substantial evidence exists. However, the majority of studies are from the US, and only one study reports findings from a developing country, limiting generalizability. The existing studies show that financial-incentive programs have placed substantial numbers of health workers in underserved areas and that program participants are more likely than non-participants to work in underserved areas in the long run, even though they are less likely to remain at the site of original placement. As none of the existing studies can fully rule out that the observed differences between participants and non-participants are due to selection effects, the evidence to date does not allow the inference that the programs have caused increases in the supply of health workers to underserved areas.</p